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  • 1.
    Jyothishkumar, V
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Numerical Flow Analysis in a Centrifugal Compressor near Surge Condition2013Ingår i: 43rd AIAA Fluid Dynamics Conference and Exhibit, 2013 / [ed] AIAA, AIAA , 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    This numerical study presents data relevant to the flow characteristics inside of a centrifugal compressor, at design and near-surge conditions. The main objectives were to characterize the flow structures and the associated instabilities near the stall point (prior to surge) and to contrast the obtained results against data acquired for a design operation condition. Generally, the operational range of compressors is limited at low mass flow rates by development of instabilities, e.g. stall and rotating stall. Such conditions lead to breakdown of the operability of the compressor, with flow reversal in the wheel passage. This results in large mass flow variations and pressure fluctuations within the compressor, lowering the compressor efficiency and pressure ratio. Large vibratory stresses are induced in the blade under such off-design operating conditions, affecting the blade life duration. Compressor stall and rotating stall are frequently regarded as “precursors” to the more damaging surge instability.  The flow fields under design and off-design operating conditions are calculated using the Large Eddy Simulation (LES) approach.  The complete geometry (360 degree) of the compressor is considered during analysis. It includes the ported shroud, the compressor wheel, the vaneless diffuser, the volute, and the exit pipe. The computationally expensive transient sliding mesh technique is used in order to capture the interaction between the wheel, the flow, and the stationary components of the compressor. The LES data are validated against available experimental measurements obtained under the same operating conditions (i.e. at design and off-design). The calculated frequency spectra when the compressor operated near-by the surge line indicated the presence of the rotating stall.

  • 2.
    Mihaescu, Mihai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Airframe Installation Effects on the Jet exhausting a Coaxial Nozzle System of a Gas Turbine Engine2012Ingår i: ASME Turbo Expo 2012 (GT2012), ASME Press, 2012, s. 347-355Konferensbidrag (Refereegranskat)
    Abstract [en]

    Jet engine installation effects can significantly affect the behavior of the exhausting flow otherwise axisymmetric for an axial-symmetric nozzle configuration. Considering the problem associated solely with the turbulent jet (i.e. neglecting jet interaction with the airframe or the flight effects) has severe limitations on accurately predicting the real case scenario. It should also be emphasized that the major sources of noise for an aircraft are the high velocity, turbulent hot jets exhausting aircraft’s gas turbine engines. Therefore, the prediction of the compressible jet by including wing and pylon effects represents today a topic of high interest in aeroacoustics.

    A numerical study is carried out for analyzing the flow associated with a separate flow nozzle system with and without installation effects. The Baseline case (without airframe installation) is compared with the case in which only the pylon is considered and with the case where the wing and the pylon are interfering with the jet engine. The simulations are performed with and without forward-flight effects. The tertiary flow increases the length of the potential core region while limiting the radial spread of the jet. The airframe installation effects increase the jet spreading underneath the pylon-nozzle-wing assembly while lowering the production of turbulence in that region. Particle Imaging Velocimetry experimental flow data are used to validate the computational results for the Baseline and the Pylon cases without the forward-flight effects.

  • 3.
    Mihaescu, Mihai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Assessment of Turbulence Models for Predicting Coaxial Jets relevant to Turbofan Engines2012Ingår i: Conference on Modelling Fluid Flow (CMFF'12) / [ed] Janos Vad, 2012, s. 716-723Konferensbidrag (Refereegranskat)
    Abstract [en]

    A numerical study is carried out for analyzing the compressible, non-isothermal flow associated with a separate-flow exhaust nozzle system with conic plug. Within the steady-state Reynolds Averaged Navier-Stokes (RANS) framework, several two-equation turbulence models among which the standard k-epsilon, the standard k-omega, and two different Shear Stress Transport (SST) k-omega formulations are evaluated. In addition, Large Eddy Simulation (LES) approach is employed for capturing the flow dynamics associated with the coaxial jet. The computational results are compared against available experimental Particle Imaging Velocimetry (PIV) flow data, in terms of time-averaged axial velocity and turbulent kinetic energy levels.

  • 4.
    Nygård, Alexander
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Altimira, M.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Prahl Wittberg, Lisa
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Analysis of vortical structures in intermittent jets2016Ingår i: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, s. 3-10Konferensbidrag (Refereegranskat)
    Abstract [en]

    The manipulation of jets has since long been subject to research, due to the wide range of industrial applications in which they are used. A vast number of numerical and experimental studies concerning the physics of the breakup process of continuous jets have been published. Improvements in mixing and ambient gas entrainment have been reported experimentally when using intermittent injection, although the responsible mechanisms have not yet been completely revealed. This work presents a systematic analysis of the mechanisms of jet breakup and mixing with the surrounding fluid and its relation to vorticity generation and transport. Comparisons aremade between the redistribution of vorticity and the engulfment of ambient fluid into the core region for different injection strategies. © Springer International Publishing Switzerland 2016.

  • 5.
    Schickhofer, Lukas
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Numerical Flow Simulations of a Flexible Plate Attached to an Obstacle in Crossflow2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    For biomedical applications with relevance to the human upper respiratory tract, the knowledge of the tissue behavior when exposed to a particular flow field would be desired. Moreover, there is of importance to quantify how the tissue properties affects the biomechanics of obstruction. Since in-vivo measurements are often not possible or inappropriate, this is assessed computationally and usually using simplified/idealized geometries.

    The present work is devoted to analyze a fluid-structure interaction scenario relevant to snoring and Obstructive Sleep Apnea Syndrome (OSAS). The uncertainty of the solution to the most influential parameters will be assessed, with the aim of quantifying the interplay between the most relevant parameters responsible for tissue self-excitation and obstruction dynamics. A statistical description of the behavior shall be developed. The tissue responsible for snoring in sleep apnea patients (the soft palate) is mimicked in this numerical study by a flexible thin plate anchored to an obstacle. The fluid-structure interaction problem is simulated computationally for several configurations in order to quantify the sensitivity of the investigation parameters onto the flow-field development.

  • 6.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Advanced Ray Tracing Techniques for Simulation of Thermal Radiation in Fluids2010Självständigt arbete på avancerad nivå (yrkesexamen), 300 hpStudentuppsats (Examensarbete)
    Abstract [en]

    For modeling thermal heat transfer, not only the effects of convection and conduction are relevant, but also thermal and visible radiation. Radiation is especially important for setups with large temperature differences, as well as for interaction with external light sources.Common computational fluid dynamic models usually treat radiation transport as a minor effect, that can be handled by simplified algorithms. All these normal models, e.g. surface to surface model, discrete transfer model, P_N method, discrete ordinates model, exhibit disadvantages in the computing performance and the physical modeling.

    Hence, there are many technical applications, where the fluid simulation are limited both in accuracy and calculation time by the available radiation model. As exemplary cases combustion chambers, smoke and soot creation, solar power generation, UV water disinfection, condensation in car headlights, fusion and fission reactor chambers, electric arc movement, as well as low-emissivity glass windows can be named.

    In the fields investigating radiation as main effect, e.g. cinematic 3d animation or illumination simulation for lamps and workspaces, the mentioned methods are not in use anymore as ray tracing is the first choice.

    In this work, the existing methods for ray tracing were adapted and implemented with the goal to interact with fluid flow simulations and replace existing radiation modeling. This can be regarded as innovative, interdisciplinary method for the interaction of fluids and solids with radiation, incorporating physical effects that could not be included in previous simulations.

    While in usual light calculations, the geometry exists solely in the form of surfaces and their triangulation, fluid flow requires volumetric calculation grids. Hence, methods are implemented that actually use the volumetric grid, and incorporate volumetric effects with little additional effort.

    Spectral volumetric path tracing with Monte Carlo integrated, importance sampled emission was hence the method of choice for this work.

    The implemented ray tracer is able to emit radiation from point sources, geometric surfaces, as well as from volumetric sources. Spectral dependence of material values is treated using radiation bands with hardly no increase of calculation time, whereas in all other models, the calculation time scales linearly with the amount of bands. Direct, diffuse and mixed surface reflection is modeled. The volumetric refraction index is implemented, so refraction is modeled, even including partial and total reflexion. The focusing of lenses or mirror systems can hence be simulated satisfactory, which cannot be treated sufficiently by any other radiation model. Surface and volumetric absorption are implemented, as well as surface and volumetric scattering effects.

    The radiation emission can be caused by a temperature field at surfaces and volumes. These fields are imported from software calculating the fluid and the thermal system. Ray tracing results in volumetric and surface heat sources that can be returned to the original code, and their effect further calculations.

    This coupling was implemented and tested with the commercial computational fluid dynamics code Fluent, using its plug-in interface. As most of Fluent's radiation models are only performed after a fixed number of implicit flow and turbulence iterations, no further disadvantages or limitations occur, that are not as well existing for the existing radiation simulations. A fully implicit treatment of radiation is unlikely to be performed, as stability is already sufficient for most applications. Of course, systems containing only heat sources caused by light and no secondary heat radiation can be treated by the implemented ray tracer with high performance.

    The implemented ray tracer is validated with analytically solved systems, and compared to quantitative simulation results of other simulation methods. Also, the scattering effects are validated against experimental and simulation results from literature.

    The observed calculation performance is similar or faster then for standard models with geometries of approximately 150000 volume elements, while the modeling is done more accurately. For larger models, even larger advantages can be expected.

  • 7.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Large Eddy Simulation of Turbulent Compressible Jets2014Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Acoustic noise pollution is an environmental aggressor in everyday life. Aero- dynamically generated noise annoys and was linked with health issues. It may be caused by high-speed turbulent free flows (e.g. aircraft jet exhausts), by airflow interacting with solid surfaces (e.g. fan noise, wind turbine noise), or it may arise within a confined flow environment (e.g. air ventilation systems, refrigeration systems). Hence, reducing the acoustic noise levels would result in a better life quality, where a systematic approach to decrease the acoustic noise radiation is required to guarantee optimal results. Computational predic- tion methods able to provide all the required flow quantities with the desired temporal and spatial resolutions are perfectly suited in such application areas, when supplementing restricted experimental investigations.

    This thesis focuses on the use of numerical methodologies in compressible flow applications to understand aerodynamically noise generation mechanisms and to assess technologies used to suppress it. Robust and fast steady-state Reynolds Averaged Navier-Stokes (RANS) based formulations are employed for the optimal design process, while the high fidelity Large Eddy Simulation (LES) approach is utilized to reveal the detailed flow physics and to investigate the acoustic noise production mechanisms. The employment of fast methods on a wide range of cases represents a brute-force strategy used to scrutinize the optimization parameter space and to provide general behavioral trends. This in combination with accurate simulations performed for particular condi- tions of interest becomes a very powerful approach. Advance post-processing techniques (i.e. Proper Orthogonal Decomposition and Dynamic Mode Decomposition) have been employed to analyze the intricate, highly turbulent flows.

    The impact of using fluidic injection inside a convergent-divergent nozzle for acoustic noise suppression is analyzed, first using steady-state RANS simulations. More than 250 cases are investigated for the optimal injection location and angle, amount of injected flow and operating conditions. Based on a-priori established criteria, a few optimal candidate solutions are detected from which one geometrical configuration is selected for being thoroughly investigated by using detailed LES calculations. This allows analyzing the unsteady shock pattern movement and the flow structures resulting with fluidic injec- tion. When investigating external fluidic injection configurations, some lead to a high amplitude shock associated noise, so-called screech tones. Such unsteady phenomena can be captured and explained only by using unsteady simulations. Another complex flow scenario demonstrated using LES is that of a high ve- locity jet ejected into a confined convergent-divergent ejector (i.e. a jet pump).

    The standing wave pattern developed in the confined channel and captured by LES, significantly alters the acoustic noise production. Steady-state methods failed to predict such events.

    The unsteady highly resolved simulations proved to be essential for analyzing flow and acoustics phenomena in complex problems. This becomes a very powerful approach when is used together with steady-state, low time-consuming formulations and when complemented with experimental measurements. 

  • 8.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Jyothishkumar, V
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Investigation of the Surge Phenomena in a Centrifugal Compressor Using Large Eddy Simulation2013Ingår i: ASME 2013 International Mechanical Engineering Congress and Exposition: 7A: Fluids Engineering Systems and Technologies, ASME Press, 2013, s. V07AT08A053-Konferensbidrag (Refereegranskat)
    Abstract [en]

    The flow through a ported shroud compressor of an automobile turbocharger is simulated using Large Eddy Simulations. Generally, the compressor is subjected to work within certain range of the mass-flow conditions. Reduction of the operation mass-flow below a certain minimum limit, leads to breakdown of the complete compressor operability. Flow reversal occurs in the compressor wheel, which results in amplification of velocity and pressure fluctuations. Consequentially, large vibratory stresses are induced into the blades under off-design condition and thereby affect the blade life duration detrimentally. The aim of this study is to understand the generation of flow-structures during extreme operable conditions (surge condition) in a centrifugal compressor. The investigation of the appearing flow-structures with the surge phenomenon is essential to explore new methods that improve the stability or the flow-operating regime of the compressor. The complete 360° compressor geometry is utilized in the computational simulations. Further, the transient sliding mesh technique is applied to account for an accurate prediction of the mesh motion and thus, the geometrical interaction between the impeller and the stationary diffuser. The numerical results are compared with available experimental measurements obtained under the same operating conditions (design and near-surge condition). The rotating stall instability is predicted using FFT data analysis. Furthermore, the numerical study captures the low frequency peak characterizing the global instability of the surge condition.

  • 9.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Kumar, Jyothish
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Gancedo, Matthieu
    University of Cincinnati.
    Numerical Flow Analysis of a Centrifugal Compressor with Ported and without Ported Shroud: 2014-01-16552014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off design operation conditions. When used, a most wide operation range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, which permits flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology on a speed-line at near optimal operation condition and near surge operation condition is investigated.

    A numerical study investigating the flow-field in a centrifugal compressor of an automotive turbocharger has been performed using Large Eddy Simulation. The wheel rotation is handled by the numerically expensive sliding mesh technique. In this analysis, the full compressor geometry (360 deg) is considered. Numerical solutions with and without ported shroud for a near optimal operation condition and near-surge operation condition. The flow-field of the different cases is analyzed to elucidate the functionality of the ported shroud. In agreement with previous observations, it was found that the ported shroud reduces the flow disturbances in the blade passage for all operating conditions. However, the compressor efficiency for the off-design operation condition was found to be higher without the ported shroud, supporting the findings reported recently by an experimental investigation. The computational results are validated with experimental measurements in terms of the performance parameters and available Particle Image Velocimetry data.

  • 10.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Laurendeau, E.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Steady-state and unsteady simulations of a high velocity jet into a venturi shaped pipe2014Ingår i: American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM, 2014, Vol. 1CKonferensbidrag (Refereegranskat)
    Abstract [en]

    A jet pump consists mainly of a convergent-divergent Ven-turi shaped duct where a primary stream is applied with the role of entraining a secondary jet. Due to their simple and reliable concept, jet pumps are used in miscellaneous applications. Performance optimization of a jet pump has to be performed for various operation conditions. Thus, numerically robust and cheap models, able to predict accurately the performance parameters of such devices are necessary. Reynolds Averaged Navier-Stokes based formulations are computationally efficient to predict the performance of a jet pump. However, these simulations rely on turbulence closure coefficients, which need to be validated with experimental observations. Large Eddy Simulation solves the most energetic structures in the flow field and it can be used to capture the flow dynamics. On the experimental side, confined geometries challenge the investigation capabilities to capture the flow field accurately and in all the details. The flow field in the jet pump is investigated using Large Eddy Simulation approach and a steady state Reynolds Averaged Navier-Stokes formulation. The flow field solutions obtained with the two numerical tools are compared. A reasonable agreement for the velocity and pressure contours could be achieved. However, the turbulence kinetic energy distribution and the entrained mass flow rate are predicted to be distinct. The difference in entrained mass flow rate leads to differences in jet pump efficiency estimation.

  • 11.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Influence of the jet location in supersonic crossflow disposed in a C-D duct2013Ingår i: Proceedings of the 26th Nordic Seminar on Computational Mechanics / [ed] Anders Logg, Kent-Andre Mardal, Andre ́ Massing, Oslo, 2013, s. 20-23Konferensbidrag (Refereegranskat)
    Abstract [en]

    The influence of shear-layer jet interaction on the flow structure generation with multiple jets in supersonic crossflow is investigated by Large Eddy Simulations (LES). A duct geometry is investigated,where the supersonic crossflow evolves in a rather sharp transition between the straight convergent and divergent section and therefore shocks establish. The jet origin location in the divergent section of the duct relative to the narrowest cross-section is significant for the shock pattern structure and the interaction point between the established separation bubble and the jets. The interaction of the separation bubble and the jets plays an important role for the flow structure generation by the jets.

  • 12.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Large Eddy Simulation of Fluidic Injection into a Supersonic Convergent-Divergent Duct2015Ingår i: DLES-9, Springer, 2015Konferensbidrag (Refereegranskat)
  • 13.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Gutmark, Ephraim
    Aerospace Engineering, University of Cincinnati.
    Analyzing the Impact of the Inlet Temperature on the Acoustic Noise Production from a Supersonic Jet using LES2013Ingår i: Proceedings of Meetings on Acoustics / [ed] Acoustical Society of America, American Institute of Physics (AIP), 2013, s. 030011-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Non-ideal expanded supersonic jets emerging from a nozzle produce three different types of noise, i.e., shock-associated broadband noise,screech noise, and the turbulent mixing noise. The screech tone occurs due to self-excitation in a feedback-loop of flow propagating downstream and acoustic wave interaction. In downscaled laboratory experiments often the screech noise occurs, while the real applied exhaustjet of a gas turbine engine does not show this phenomena. Apart from a geometric scaling difference, usually a lower temperature is employed in experimental studies. The compressible Navier-Stokes equations are simulated numerically by a large eddy simulation approach to investigate the effect of jet operation temperature onto the noise development in a supersonic jet originating from a convergent-divergent nozzle. The jet-exit Mach-number is 1.56, while the total temperature ratios are 1.27, 2.46, and 3.65. The differences in the acoustic near-field will be presented and the interaction of flow-field with acoustic waves will be analyzed and compared to each other.

  • 14.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    Large Eddy Simulations of Microjets Impact on Supersonic Jet Exiting a C-D Conical Nozzle2013Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The effect of multiple microjets on the acoustic noise production originating from a super-sonic jet exhausting a gas turbine engine is studied numerically using the Large Eddy Simulation (LES) approach. The nozzle exit design Mach-number is 1.56, while the total temperature ratio is kept to 1.27. The nozzle contour is a double cone converging- diverging nozzle. The emerging jet is slightly over-expanded. A double shock-diamond pattern develops in the supersonic flow. The study focuses on the changes in the flow pattern, the shock-associated noise and the radiated near-field acoustics when using fluidics as compared with a baseline, (i.e. without fluidics).

    Just downstream of the nozzle lip, twelve cylindrical microjets are placed circumferentially, with a 60 inclination angle towards the nozzle centerline axis, in the streamwise flow direction. The pressurized mass-flow feeding the microjets is assumed to be initially at ambient conditions. The amount of pressurization is given as an Injection Pressure Ratio (IPR) and represents the investigation parameter.

    Acoustic based experiments performed at University of Cincinnati (UC) exhibited acous- tic benefit when using the mentioned set-up for the microjets. However, the impact that injection had on the flow-field was dicult to be quantified. Thus, LES calculations have been performed to analyze the compressible flow-field, the shock-structure alteration and thrust evaluations associated with the fluidics. 

  • 15.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Numerical Investigation of Fluidic Control on Supersonic Jet of a Gas Turbine Engine2012Ingår i: 20th International Shock Interaction Symposium (ISIS 20) / [ed] Nicholas Apazidis, ISIS, KTH , 2012, s. 161-164Konferensbidrag (Refereegranskat)
    Abstract [en]

    Use of fluidics on the supersonic flow exhausting a gas turbine engine is investigated. The purpose is to control the shock-waves i.e., their location and strength by using injection tubes disposed on the circumference of the nozzle. A parametric study has been performed for quantifying the effect on shock patterns of different parameters such the nozzle pressure ratio, the injection pressure ratio, location and inclination of the tubes. Different cases have been screened, using the steady-state Reynolds-averaged Navier-Stokes formulation. For the Baseline case (without injection) at the design conditions, a grid convergence study was performed and the results were compared with experimental Particle Imaging Velocimetry data. An overall fair agreement was found. In contrast with the Baseline, significant changes in shear-layer shape, mixing, and turbulence intensity are associated with vortical structures generated due to fluidic injection. With an appropriate choice of injection parameters the ability to shift or move shocks and reduce shock strength is proven. Improvement in terms of better mixing, better thrust performance, and the possibility of reducing acoustic radiation can be shown for some of the cases.

  • 16.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Gutmark, Ephraim
    University of Cincinnati.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Flow Structure Generation by Multiple Jets in Supersonic Cross-Flow2013Ingår i: 4th International Conference on Jets, Wakes and Separated Flows, ICJWSF2013, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    The flow structure generation by multiple jets impinging a supersonic crossflow in the divergent section of a Convergent-Divergent (C-D) duct is investigated using compressible Large Eddy Simulations (LES). The supersonic flow-field in the C-D duct is mainly characterized by the evolving shock-structure. The effect of increasing the compressible jet to crossflow velocity ratio R to the generation of flow structures and the ability to modify the shock-pattern in the duct was studied. Traversing R, the shock-pattern can be significantly altered. This paper demonstrates that for close located jets in crossflow the vortical structures generated by the jets can interact and give rise to vortical structures in the interspace plane between the jets. The spectra for different probes are shown illustrating the characteristic flow frequencies. For all simulated cases the spectra show peaks for a defined Strouhal-number of 0.5. The jets choke in the crossflow above an R of about 0.65, which results in a faster disruption of the coherent flow structures induced by the jets. The flow field is analyzed using Proper Orthogonal Decomposition (POD).

  • 17.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Wang, Yue
    Northwestern Polytechnical University, China.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Flow effects due to pulsation in an internal combustion engine exhaust port2014Ingår i: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 86, s. 520-536Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In an internal combustion engine, the residual energy remaining after combustion in the exhaust gasses can be partially recovered by a downstream arranged device. The exhaust port represents the passage guiding the exhaust gasses from the combustion chamber to the energy recovering device, e.g. a turbocharger. Thus, energy losses in the course of transmission shall be reduced as much as possible. However, in one-dimensional engine models used for engine design, the exhaust port is reduced to its discharge coefficient, which is commonly measured under constant inflow conditions neglecting engine-like flow pulsation. In this present study, the influence of different boundary conditions on the energy losses and flow development during the exhaust stroke are analyzed numerically regarding two cases, i.e. using simple constant and pulsating boundary conditions. The compressible flow in an exhaust port geometry of a truck engine is investigated using three-dimensional Large Eddy Simulations (LES). The results contrast the importance of applying engine-like boundary conditions in order to estimate accurately the flow induced losses and the discharge coefficient of the exhaust port. The instantaneous flow field alters significantly when pulsating boundary conditions are applied. Thus, the induced losses by the unsteady flow motion and the secondary flow motion are increased with inflow pulsations. The discharge coefficient decreased about 2% with flow pulsation. A modal flow decomposition method, i.e. Proper Orthogonal Decomposition (POD), is used to analyze the coherent structures induced with the particular inflow and outflow conditions. The differences in the flow field for different boundary conditions suggest to incorporate a modeling parameter accounting for the quality of the flow at the turbocharger turbine inlet in one-dimensional simulations.

  • 18.
    Semlitsch, Bernhard
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Wang, Yue
    Northwestern Polytechnical University.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Flow effects due to valve and piston motion in an internal combustion engine exhaust port2015Ingår i: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 96, s. 18-30Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Performance optimization regarding e.g. exhaust valve strategies in an internal combustion engine is often performed based on one-dimensional simulation investigation. Commonly, a discharge coefficient is used to describe the flow behavior in complex geometries, such as the exhaust port. This discharge coefficient for an exhaust port is obtained by laboratory experiments at fixed valve lifts, room tem- peratures, and low total pressure drops. The present study investigates the consequences of the valve and piston motion onto the energy losses and the discharge coefficient. Therefore, Large Eddy Simulations are performed in a realistic internal combustion geometry using three different modeling strategies, i.e. fixed valve lift and fixed piston, moving piston and fixed valve lift, and moving piston and moving valve, to estimate the energy losses. The differences in the flow field development with the different modeling approaches is delineated and the dynamic effects onto the primary quantities, e.g. discharge coefficient, are quantified. Considering the motion of piston and valves leads to negative total pressure losses during the exhaust cycle, which cannot be observed at fixed valve lifts. Additionally, the induced flow structures develop differently when valve motion is taken into consideration, which leads to a significant disparity of mass flow rates evolving through the two individual valve ports. However, accounting for piston motion and limited valve motion, leads to a minor discharge coefficient alteration of about one to two percent. 

  • 19.
    Sundström, Elias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI).
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Assessment of the 3D Flow in a Centrifugal compressor using Steady-State and Unsteady Flow Solvers2014Ingår i: SAE Technical Paper, 2014-01-2856, 2014, SAE International , 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Numerical analysis methods are used to investigate the flow in a ported-shroud centrifugal compressor under different operating conditions, i.e. several mass flow rates at two different speed lines. A production turbocharger compressor is considered, which is widely used in the heavy automotive sector. Flow solutions obtained under steady-state and transient flow assumptions are compared with available experimental data.

    The steady-state Reynolds Averaged Navier-Stokes method is used to assess the overall time averaged flow and the global performance parameters. Additionally, the Large Eddy Simulation (LES) approach is employed to capture the transient flow features and the developed flow instabilities at low mass flow rates near the surge line.

    The aim of this study is to provide new insights on the flow instability phenomena in the compressor flow near surge. Comparison of flow solutions obtained for near-optimal efficiency and near-surge conditions are carried out. The unsteady features of the flow field are quantified by means of Fourier transformation analysis, Proper Orthogonal Decomposition and Dynamic Mode Decomposition. For a near optimal efficiency set-up the frequency spectra are broad- banded with no distinct instabilities. Close to the surge line, the spectra show a distinct surge cycle frequency, which is due to flow pulsation in the compressor.

    The modal flow decomposition elucidates a mode occurring at the surge frequency. The mode explains the oscillating pumping effect occurring during surge. The surface spectra contours reveal the shape of the pressure pulsation during surge and support that a pressure gradient occurs with the oscillating modes found with the modal decomposition. 

  • 20.
    Sundström, Elias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strömningsfysik.
    Centrifugal Compressor: The Sound of Surge2015Ingår i: 21st AIAA/CEAS Aeroacoustics Conference, 2015, s. 1-17Konferensbidrag (Refereegranskat)
    Abstract [en]

    When the centrifugal compressor operates at low mass flow rates (close to the unstable operating condition called surge), flow instabilities may develop and severe flow reversal may occur in the wheel passage. Under such conditions, noise generation has been reported resulting in a notable discomfort induced to the passengers in the cabin.

    The aim with this study is to predict the flow field associated with a centrifugal compressor and characterize the acoustic near-field generation and propagation under stable and off-design (near-surge) operating conditions. The Large Eddy Simulation (LES) approach is employed. The unsteady features in the flow field leading to acoustic noise generation are quantified by means of statistical averaging, Fourier data analysis and flow mode decomposition techniques. The decomposition method is performed inside the rotating impeller region for several stable and off-design (including surge and near-surge) operating condi- tions. The acoustic near-field data are presented in terms of noise directivity maps and sound pressure level spectra.

    For the near-surge condition an amplified broadband feature at two times the frequency of the rotating order of the shaft (possible whoosh noise) was captured. However, an amplified feature around 50% of the rotating order was captured as well. These features are present also during the investigated surge operating conditions, but occur at lower amplitudes as compared with the captured low surge frequency of 43 Hz. 

  • 21.
    Sundström, Elias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Semlitsch, Bernhard
    University of Cambridge, UK.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Generation Mechanisms of Rotating Stall and Surge in Centrifugal Compressors2018Ingår i: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 100, nr 3, s. 705-719Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Flow instabilities such as Rotating Stall and Surge limit the operating range of centrifugal compressors at low mass-flow rates. Employing compressible Large Eddy Simulations (LES), their generation mechanisms are exposed. Toward low mass-flow rate operating conditions, flow reversal over the blade tips (generated by the back pressure) causes an inflection point of the inlet flow profile. There, a shear-layer induces vortical structures circulating at the compressor inlet. Traces of these flow structures are observed until far downstream in the radial diffuser. The tip leakage flow exhibits angular momentum imparted by the impeller, which deteriorates the incidence angles at the blade tips through an over imposed swirling component to the incoming flow. We show that the impeller is incapable to maintain constant efficiency at surge operating conditions due to the extreme alteration of the incidence angle. This induces unsteady flow momentum transfer downstream, which is reflected as compression wave at the compressor outlet traveling toward the impeller. There, the pressure oscillations govern the tip leakage flow and hence, the incidence angles at the impeller. When these individual self-exited processes occurs in-phase, a surge limit-cycle establishes.

  • 22.
    Sundström, Elias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Similarities and differences concerning flow characteristics in centrifugal compressors of different size2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    The appropriate choice of an automotive turbocharger compressor for an internal combustion engine is based on the compressor performance, which is commonly specified on a compressor map for different operating conditions. A wide operating range for the compressor covering all possible engine working conditions is desired. However, the application range of the compressor is limited. Different compressor designs are used to fit specific engine requirements. Naturally, these will have rather different characteristic compressor maps. The aim of the present investigation is to explain the differences in the compressor maps by analyzing the compressible flow-fields in two compressor designs from the same manufacturer, intended for a light-duty vehicle (passenger car). The flow-fields are assessed by steady-state Reynolds Averaged Navier-Stokes (RANS) simulations for several operating conditions. Similar flow features are observed near optimal efficiency operating conditions when the flow-field parameters are scaled properly. This study exposes the reason for the different measured operating ranges of the two compressors when ran at the same speed lines.

  • 23. Wang, Yue
    et al.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Flow Induced Energy Losses in the Exhaust Port of an Internal Combustion Engine2014Ingår i: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 137, nr 1, s. 011105-01-011105-09Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A numerical study of the flow in the exhaust port geometry of a Scania heavy-duty diesel engine is performed using the large eddy simulation (LES) and an unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation approach. The calculations are performed at fixed valve positions and stationary boundary conditions to mimic the setup of an air flow bench experiment, which is commonly used to acquire input data for one-dimensional engine simulations. The numerical results are validated against available experimental data. The complex three-dimensional (3D) flow structures generated in the flow field are qualitatively assessed through visualization and analyzed by statistical means. For low valve lifts, the major source of kinetic energy losses occurs in the proximity of the valve. Flow separation occurs immediately downstream of the valve seat. Strong helical flow structures are observed in the exhaust manifold, which are caused due an interaction of the exhaust port streams in the port geometry.

  • 24.
    Wang, Yue
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för industriell teknik och management (ITM), Centra, Competence Center for Gas Exchange (CCGEx).
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Flow structures and losses in the exhaust port of an internal combustion engine2014Ingår i: ASME 2013 International Mechanical Engineering Congress & Exposition: Fluids Engineering Systems and Technologies, ASME Press, 2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    A numerical study of the flow in the exhaust port geometry of a Scania heavy-duty Diesel engine is carried out mainly by using the Large Eddy Simulation (LES) approach. Unsteady Reynolds Averaged Navier-Stokes (URANS) simulation results are included for comparison purposes. The calculations are performed with fixed valve and stationary boundary conditions for which experimental data are available. The simulations include a verification study of the solver using different grid resolutions and different valve lift states. The calculated numerical data are compared to existent measured pressure loss data. The results show that even global parameters like total pressure losses are predicted better by LES than by URANS. The complex three-dimensional flow structures generated in the flow field are qualitatively assessed through visualization and analyzed by statistical means. The near valve region is a major source of losses. Due to the presence of the valve, an annular, jet-like flow structure is formed where the high-velocity flow follows the valve stem into the port. Flow separation occurs immediately downstream of the valve seat on the walls of the port and also on the surface of the valve body. Strong longitudinal, non-stationary secondary flow structures (i.e. in the plane normal to the main flow direction) are observed in the exhaust manifold. Such structures can degrade the efficiency of a possible turbine of a turbocharger located downstream on the exhaust manifold.

  • 25.
    Wang, Yue
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Semlitsch, Bernhard
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Mihaescu, Mihai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Flow-structures Generated by Valve and Piston Motion in an Exhaust Port of a Truck Engine2013Ingår i: Proceedings of the 4th International Conference on Jets, Wakes and Separated Flows-IV, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    The exhaust port of a truck internal combustion engine forms the interface between the combustion engine and the turbocharger. Approximately 30-40% of the energy potential is lost in the exhaust gasses after combustion, which can be partially recuperated in a turbocharger. Hence, energy losses in the connection are highly undesired. However, due to the high occurring velocities and the complex geometry, flow separation, flowstructure formation, and secondary flow motion are the major sources of energy losses. Within the exhaust process, the valves open while the piston continues moving in the combustion camber. This process is often analyzed by modeling the piston and valves at fixed locations, but conserving the total mass flow. Using advanced methods, this process can be simulated numerically in a more accurate manner. This study compares Large Eddy Simulation based data, assessing the implied differences due to the choise of method for simulating the exhaust process from an engine cylinder. A simple case using fixed positions for valve and piston is contrasted with the cases where static valve and moving piston, and moving valve and moving piston are considered, respectively. The generated flow phenomena are  compared within the cases.

1 - 25 av 25
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