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Semlitsch, B. & Huscava, A. (2022). Shape Optimisation of Turbomachinery Components. In: : . Paper presented at The 8th European Congress on Computational Methods in Applied Sciences and Engineering - ECCOMAS Congress 2022. Scipedia, S.L.
Open this publication in new window or tab >>Shape Optimisation of Turbomachinery Components
2022 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Low-order models are the first choice to find the initial design of turbomachinery components screening many configurations. The final optimisation of the three-dimensional geometry is crucial for the best performance. Because of the ability to accurately predict the performance of turbomachinery, fluid dynamic simulations became a powerful tool [10]. However, parameter studies for shape optimisation relying on fluid dynamic simulations are computationally expensive and might fail to reveal the optimal geometry. Gradient-based optimisation approaches allow a significant reduction of simulations and hence, determine the optimum efficiency. The adjoint method finds the optimisation gradient by calculating the derivatives of the state variables with respect to the design objective without the need for finite differences [6]. Thus, the adjoint optimisation is especially efficient for problems with many degrees of freedom and few design objectives, e.g. increasing efficiency. The application of the adjoint method for shape optimisation is demonstrated on the example of a centrifugal compressor impeller. The shape of the rotor blades is optimised, and the impact of different objection functions, i.e. reducing the required moment or increasing the achieved pressure ratio, and optimisation constraints, i.e. retaining the operating point or keeping an area ratio, is analysed. The results demonstrate that the compressor performance can be significantly improved using the adjoint method. However, the challenge is to obtain not only an optimised shape for operating points but also for the entire operating map. The final shapes, obtained for different operating points, are compared. 

Place, publisher, year, edition, pages
Scipedia, S.L., 2022
Keywords
Computational Fluid Dynamics, Shape Optimisation, Rotating Impeller, Turbomachinery Design
National Category
Fluid Mechanics Energy Engineering Aerospace Engineering
Research subject
Aerospace Engineering; Applied and Computational Mathematics, Optimization and Systems Theory
Identifiers
urn:nbn:se:kth:diva-322765 (URN)10.23967/eccomas.2022.244 (DOI)
Conference
The 8th European Congress on Computational Methods in Applied Sciences and Engineering - ECCOMAS Congress 2022
Note

QC 20230117

Available from: 2023-01-04 Created: 2023-01-04 Last updated: 2025-02-09Bibliographically approved
Semlitsch, B. & Mihăescu, M. (2021). Evaluation of Injection Strategies in Supersonic Nozzle Flow. Aerospace, 8(12), 369-369
Open this publication in new window or tab >>Evaluation of Injection Strategies in Supersonic Nozzle Flow
2021 (English)In: Aerospace, ISSN 2226-4310, Vol. 8, no 12, p. 369-369Article in journal (Refereed) Published
Abstract [en]

The ability to manipulate shock patterns in a supersonic nozzle flow with fluidic injection is investigated numerically using Large Eddy Simulations. Various injector configurations in the proximity of the nozzle throat are screened for numerous injection pressures. We demonstrate that fluidic injection can split the original, single shock pattern into two weaker shock patterns. For intermediate injection pressures, a permanent shock structure in the exhaust can be avoided. The nozzle flow can be manipulated beneficially to increase thrust or match the static pressure at the discharge. The shock pattern evolution of injected stream is described over various pressure ratios. We find that the penetration depth into the supersonic crossflow is deeper with subsonic injection. The tight arrangement of the injectors can provoke additional counter-rotating vortex pairs in between the injection.

Place, publisher, year, edition, pages
MDPI, 2021
Keywords
flow control; supersonic nozzle flow; loss reduction
National Category
Fluid Mechanics Aerospace Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-305930 (URN)10.3390/aerospace8120369 (DOI)000735780600001 ()2-s2.0-85121839594 (Scopus ID)
Note

QC 20211209

Available from: 2021-12-09 Created: 2021-12-09 Last updated: 2025-02-09Bibliographically approved
Semlitsch, B., Cuppoletti, D., Gutmark, E. & Mihaescu, M. (2019). Transforming the Shock Pattern of Supersonic Jets using Fluidic Injection. AIAA Journal, 57(5), 1851-1861
Open this publication in new window or tab >>Transforming the Shock Pattern of Supersonic Jets using Fluidic Injection
2019 (English)In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 57, no 5, p. 1851-1861Article in journal (Refereed) Published
Abstract [en]

Double shock diamonds establish in the exhaust of modular convergent–divergent nozzles. These consist of two shock structures: one originating from the nozzle throat, and another from its exit. Analyzing the shock pattern developing for different fluidic injection operating conditions, it is shown that fluidic injection allows the rearrangement of the shock structures relative to each other. Overlapping the two structures causes large pressure oscillations in the exhaust and high amplitudes of shock associated noise, whereas staggering the shock structures mitigates these effects. The screech tone frequency does not change for all injection operating configurations, although the shock diamonds are shifted drastically with respect to each other. Hence, the screech phenomenon is dominated by the primary shock spacing originating from the nozzle throat.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2019
Keywords
Acoustic Noise Reduction, Supersonic Jet
National Category
Aerospace Engineering Fluid Mechanics
Identifiers
urn:nbn:se:kth:diva-271563 (URN)10.2514/1.J057629 (DOI)000484818400007 ()2-s2.0-85066791610 (Scopus ID)
Note

QC 20200624

Available from: 2020-03-26 Created: 2020-03-26 Last updated: 2025-02-09Bibliographically approved
Sundström, E., Semlitsch, B. & Mihaescu, M. (2018). Acoustic signature of flow instabilities in radial compressors. Journal of Sound and Vibration, 434, 221-236
Open this publication in new window or tab >>Acoustic signature of flow instabilities in radial compressors
2018 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 434, p. 221-236Article in journal (Refereed) Published
Abstract [en]

Rotating stall and surge are flow instabilities contributing to the acoustic noise generated in centrifugal compressors at low mass flow rates. Their acoustic generation mechanisms are exposed employing compressible Large Eddy Simulations (LES). The LES data are used for calculating the dominant acoustic sources emerging at low mass flow rates. They give the inhomogeneous character of the Ffowcs Williams and Hawkings (FW-H) wave equation. The blade loading term associated with the unsteady pressure loads developed on solid surfaces (dipole in character) is found to be the major contributor to the aerodynamically generated noise at low mass flow rates. The acoustic source due to the velocity variations and compressibility effects (quadrupole in character) as well as the acoustic source caused by the displacement of the fluid due to the accelerations of the solid surfaces (monopole in character) were found to be not as dominant. We show that the acoustic source associated with surge is generated by the pressure oscillation, which is governed by the tip leakage flow. The vortical structures of rotating stall are interacting with the impeller. These manipulate the flow incidence angles and cause thereby unsteady blade loading towards the discharge. A low-pressure sink between 4 and 6 o'clock causes a halving of the perturbation frequencies at low mass flow rates operating conditions. From two point space-time cross correlation analysis based on circumferential velocity in the diffuser it was found that the rotating stall cell propagation speed increases locally in the low pressure zone under the volute tongue. It was also found that rotating stall can coexist with surge operating condition, but the feature is then seen to operate over a broader frequency interval.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Large Eddy Simulations, Rotating stall, Surge, Acoustics source, Centrifugal compressor
National Category
Fluid Mechanics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-233576 (URN)10.1016/j.jsv.2018.07.040 (DOI)000444001700013 ()2-s2.0-85051117612 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20180830

Available from: 2018-08-25 Created: 2018-08-25 Last updated: 2025-02-09Bibliographically approved
Sundström, E., Semlitsch, B. & Mihaescu, M. (2018). Generation Mechanisms of Rotating Stall and Surge in Centrifugal Compressors. Flow Turbulence and Combustion, 100(3), 705-719
Open this publication in new window or tab >>Generation Mechanisms of Rotating Stall and Surge in Centrifugal Compressors
2018 (English)In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 100, no 3, p. 705-719Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Rotating stall, Surge, Centrifugal compressor, Large Eddy Simulations, LES
National Category
Engineering and Technology
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-218399 (URN)10.1007/s10494-017-9877-z (DOI)000426863700006 ()30069143 (PubMedID)2-s2.0-85034781553 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20171211

Available from: 2017-11-28 Created: 2017-11-28 Last updated: 2024-03-18Bibliographically approved
Nygård, A., Altimira, M., Semlitsch, B., Prahl Wittberg, L. & Fuchs, L. (2016). Analysis of vortical structures in intermittent jets. In: Springer Proceedings in Physics: . Paper presented at 5th International Conference on Jets, Wakes and Separated Flows, ICJWSF2015, 15 June 2015 through 18 June 2015 (pp. 3-10). Springer Science+Business Media B.V.
Open this publication in new window or tab >>Analysis of vortical structures in intermittent jets
Show others...
2016 (English)In: Springer Proceedings in Physics, Springer Science+Business Media B.V., 2016, p. 3-10Conference paper, Published paper (Refereed)
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. 

Place, publisher, year, edition, pages
Springer Science+Business Media B.V., 2016
Keywords
Industrial research, Mixing, Transport properties, Vorticity, Wakes, Ambient fluids, Ambient gas, Continuous jets, Intermittent injection, Numerical and experimental study, Systematic analysis, Vortical structures, Vorticity generation, Fighter aircraft
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-195137 (URN)10.1007/978-3-319-30602-5_1 (DOI)000387431400001 ()2-s2.0-84978998403 (Scopus ID)9783319306001 (ISBN)
Conference
5th International Conference on Jets, Wakes and Separated Flows, ICJWSF2015, 15 June 2015 through 18 June 2015
Note

QC 20240110

Available from: 2016-11-16 Created: 2016-11-02 Last updated: 2024-01-10Bibliographically approved
Schickhofer, L., Semlitsch, B. & Mihaescu, M. (2016). Numerical Flow Simulations of a Flexible Plate Attached to an Obstacle in Crossflow. In: : . Paper presented at International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015). Springer
Open this publication in new window or tab >>Numerical Flow Simulations of a Flexible Plate Attached to an Obstacle in Crossflow
2016 (English)Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
Springer, 2016
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 185
Keywords
Snoring
National Category
Fluid Mechanics
Research subject
Biological Physics
Identifiers
urn:nbn:se:kth:diva-171230 (URN)10.1007/978-3-319-30602-5_25 (DOI)000387431400025 ()2-s2.0-84978933952 (Scopus ID)978-3-319-30600-1 (ISBN)
Conference
International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015)
Note

QC 20150804. QC 20160226

Available from: 2015-07-24 Created: 2015-07-24 Last updated: 2025-02-09Bibliographically approved
Sundström, E., Semlitsch, B. & Mihaescu, M. (2016). Similarities and differences concerning flow characteristics in centrifugal compressors of different size. In: : . Paper presented at International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015). Springer
Open this publication in new window or tab >>Similarities and differences concerning flow characteristics in centrifugal compressors of different size
2016 (English)Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
Springer, 2016
Series
Springer Proceedings in Physics, ISSN 0930-8989 ; 185
Keywords
Centrifugal Compressor, Turbocharger, Fuel Efficiency
National Category
Fluid Mechanics
Research subject
Aerospace Engineering; Energy Technology
Identifiers
urn:nbn:se:kth:diva-171231 (URN)10.1007/978-3-319-30602-5_57 (DOI)000387431400057 ()2-s2.0-84979080235 (Scopus ID)978-331930600-1 (ISBN)
Conference
International Conference on Jets, Wakes and Separated Flows ( ICJWSF2015)
Funder
Swedish Energy Agency
Note

QC 20150805

Available from: 2015-07-24 Created: 2015-07-24 Last updated: 2025-02-09Bibliographically approved
Sundström, E., Semlitsch, B. & Mihaescu, M. (2015). Centrifugal Compressor: The Sound of Surge. In: 21st AIAA/CEAS Aeroacoustics Conference: . Paper presented at 21st AIAA/CEAS Aeroacoustics Conference, Meeting Location: Dallas, TX, 22-25 June 2015 (pp. 1-17).
Open this publication in new window or tab >>Centrifugal Compressor: The Sound of Surge
2015 (English)In: 21st AIAA/CEAS Aeroacoustics Conference, 2015, p. 1-17Conference paper, Published paper (Refereed)
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. 

Keywords
Acoustic waves, Aeroacoustics, Centrifugal compressors, Centrifugation, Flow fields, Fourier series, Large eddy simulation, Decomposition methods, Flow instabilities, Low mass flow rates, Noise generation, Operating condition, Rotating impellers, Sound pressure level, Statistical Averaging, Acoustic noise
National Category
Fluid Mechanics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-169882 (URN)10.2514/6.2015-2674 (DOI)2-s2.0-84962514109 (Scopus ID)978-1-62410-367-4 (ISBN)
Conference
21st AIAA/CEAS Aeroacoustics Conference, Meeting Location: Dallas, TX, 22-25 June 2015
Note

QC 20160616

Available from: 2015-06-24 Created: 2015-06-24 Last updated: 2025-02-09Bibliographically approved
Semlitsch, B., Wang, Y. & Mihaescu, M. (2015). Flow effects due to valve and piston motion in an internal combustion engine exhaust port. Energy Conversion and Management, 96, 18-30
Open this publication in new window or tab >>Flow effects due to valve and piston motion in an internal combustion engine exhaust port
2015 (English)In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 96, p. 18-30Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Internal combustion engines, Fuel economy, Turbocharged engines, Exhaust gas energy, Large Eddy Simulation
National Category
Fluid Mechanics
Research subject
Vehicle and Maritime Engineering
Identifiers
urn:nbn:se:kth:diva-161210 (URN)10.1016/j.enconman.2015.02.058 (DOI)000353729200003 ()2-s2.0-84924262331 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20150311

Available from: 2015-03-10 Created: 2015-03-10 Last updated: 2025-02-09Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7715-863X

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