Change search
Link to record
Permanent link

Direct link
BETA
Alternative names
Publications (10 of 130) Show all publications
Discetti, S., Bellani, G., Örlü, R., Serpieri, J., Sanmiguel Vila, C., Raiola, M., . . . Ianiro, A. (2019). Characterization of very-large-scale motions in high-Re pipe flows. Experimental Thermal and Fluid Science, 1-8
Open this publication in new window or tab >>Characterization of very-large-scale motions in high-Re pipe flows
Show others...
2019 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, p. 1-8Article in journal (Refereed) Published
Abstract [en]

Very-large-scale structures in pipe flows are characterized using an extended Proper Orthogonal Decomposition (POD)-based estimation. Synchronized non-time-resolved Particle Image Velocimetry (PIV) and time-resolved, multi-point hot-wire measurements are integrated for the estimation of turbulent structures in a pipe flow at friction Reynolds numbers of 9500 and 20000. This technique enhances the temporal resolution of PIV, thus providing a time-resolved description of the dynamics of the large-scale motions. The experiments are carried out in the CICLoPE facility. A novel criterion for the statistical characterization of the large-scale motions is introduced, based on the time-resolved dynamically-estimated POD time coefficients. It is shown that high-momentum events are less persistent than low-momentum events, and tend to occur closer to the wall. These differences are further enhanced with increasing Reynolds number.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Boundary layer, Pipe flow, POD, Very-large-scale motions
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-246414 (URN)10.1016/j.expthermflusci.2019.02.001 (DOI)000465055600001 ()2-s2.0-85061452509 (Scopus ID)
Note

QC 20190401

Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-05-14Bibliographically approved
Borodulin, V. I., Ivanov, A. V., Kachanov, Y. S., Mischenko, D. A., Örlü, R., Hanifi, A. & Hein, S. (2019). Experimental and theoretical study of swept-wing boundary-layer instabilities. Unsteady crossflow instability. Physics of fluids, 31(6), Article ID 064101.
Open this publication in new window or tab >>Experimental and theoretical study of swept-wing boundary-layer instabilities. Unsteady crossflow instability
Show others...
2019 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 31, no 6, article id 064101Article in journal (Refereed) Published
Abstract [en]

Extensive combined experimental and theoretical investigations of the linear evolution of unsteady (in general) Cross-Flow (CF) and three-dimensional (3D) Tollmien-Schlichting (TS) instability modes of 3D boundary layers developing on a swept airfoil section have been carried out. CF-instability characteristics are investigated in detail at an angle of attack of -5 degrees when this kind of instability dominates in the laminar-turbulent transition process, while the 3D TS-instability characteristics are studied at an angle of attack of +1.5 degrees when this kind of instability is predominant in the transition process. All experimental results are deeply processed and compared with results of calculations based on several theoretical approaches. For the first time, very good quantitative agreement of all measured and calculated stability characteristics of swept-wing boundary layers is achieved both for unsteady CF- and 3D TS-instability modes for the case of a boundary layer developing on a real swept airfoil. The first part of the present study (this paper) is devoted to the description of the case of CF-dominated transition, while the TS-dominated case will be described in detail in a subsequent second part of this investigation.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2019
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-255496 (URN)10.1063/1.5094609 (DOI)000474440800020 ()2-s2.0-85067248795 (Scopus ID)
Note

QC 20190919

Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-09-19Bibliographically approved
Guemes, A., Vila, C. S., Örlü, R., Vinuesa, R., Schlatter, P., Ianiro, A. & Discetti, S. (2019). Flow organization in the wake of a rib in a turbulent boundary layer with pressure gradient. Experimental Thermal and Fluid Science, 108, 115-124
Open this publication in new window or tab >>Flow organization in the wake of a rib in a turbulent boundary layer with pressure gradient
Show others...
2019 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 108, p. 115-124Article in journal (Refereed) Published
Abstract [en]

The effect of a streamwise pressure gradient on the wake developed by wall-attached square ribs in a turbulent boundary layer is investigated experimentally. Favourable-, adverse- and zero-pressure-gradient conditions (FPG, APG and ZPG, respectively) are reproduced at matched friction Reynolds number and non-dimensional rib height. Flow-field measurements are carried out by means of Particle Image Velocimetry (PIV). Turbulence statistics are extracted at high resolution using an Ensemble Particle Tracking Velocimetry approach. Modal analysis is performed with Proper Orthogonal Decomposition (POD). We demonstrate that a non-dimensional expression of the pressure gradient and shear stress is needed to quantify the pressure-gradient effects in the wake developing past wall-attached ribs. We suggest the Clauser pressure-gradient parameter beta, commonly used in the literature for the characterization of turbulent boundary layers under the effect of a pressure gradient, as a suitable parameter. The results show that, in presence of an adverse pressure gradient, the recirculation region downstream of the rib is increased in size, thus delaying the reattachment, and that the peak of turbulence intensity and the shed eddies are shifted towards larger wall-normal distances than in the ZPG case. The observed changes with respect to the ZPG configuration appear more intense for larger magnitude of beta, which are more likely to be obtained in APG than in FPG due to the reduced skin friction and increased displacement thickness.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE INC, 2019
Keywords
Turbulent boundary layer, Pressure gradient flows, Ribs
National Category
Fluid Mechanics and Acoustics
Research subject
Applied and Computational Mathematics, Numerical Analysis
Identifiers
urn:nbn:se:kth:diva-260990 (URN)10.1016/j.expthermflusci.2019.05.022 (DOI)000484651400012 ()2-s2.0-85068442439 (Scopus ID)
Note

QC 20191003

Available from: 2019-10-03 Created: 2019-10-03 Last updated: 2019-11-26Bibliographically approved
Mallor, F., Raiola, M., Sanmiguel Vila, C., Örlü, R., Discetti, S. & Ianiro, A. (2019). Modal decomposition of flow fields and convective heat transfer maps: An application to wall-proximity square ribs. Experimental Thermal and Fluid Science, 517-527
Open this publication in new window or tab >>Modal decomposition of flow fields and convective heat transfer maps: An application to wall-proximity square ribs
Show others...
2019 (English)In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, p. 517-527Article in journal (Refereed) Published
Abstract [en]

In this work the modal decomposition of convective heat transfer distributions in turbulent flows is explored. The organization and thermal footprint of the turbulent flow features generated downstream of wall-proximity two-dimensional square ribs immersed in a turbulent boundary layer are investigated experimentally. This study employs modal decomposition to investigate whether this analysis can allow identifying which characteristics of the flow topology are responsible for the Nusselt-number augmentation, aiming to uncover the underlying physics of heat-transfer enhancement. Heat transfer and flow velocity measurements are performed at a Reynolds number (based on the free-stream velocity and rib side-length) equal to 4600. Square ribs are tested for two different gap spacings from the wall (0.25 and 0.5 ribs side-length) and in wall-attached configuration. A low-thermal-inertia heat transfer sensor coupled with high-repetition-rate Infrared (IR) thermography is designed to study the unsteady variation of the convective heat-transfer coefficient downstream of the obstacles. Flow-field measurements are performed with non-time-resolved Particle Image Velocimetry (PIV). A modal analysis with Proper Orthogonal Decomposition (POD) is applied to both convective heat-transfer maps and velocity-fields. The comparison of the Nusselt-number spatial modes of the clean turbulent boundary layer configuration and of the configurations with the ribs shows a variation of the spatial pattern associated with oscillations with strong spanwise coherence, opposed to the thin elongated streaks which dominate the convective heat transfer in the clean turbulent boundary layer. In configurations where the convective heat transfer is enhanced by coherent structures located close to the wall, similar eigenspectra are observed for both flow field and convective heat transfer modes. The results of the modal analysis support a picture of a direct relation between the coherence of near-wall flow features and heat-transfer augmentation, providing a statistical evidence for the fact that near-wall coherent eddies are extremely efficient in enhancing heat transfer.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
IR thermography, POD, Rib turbulators, Turbulent boundary layers, Unsteady turbulent convection
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-246469 (URN)10.1016/j.expthermflusci.2018.12.023 (DOI)000457667800043 ()2-s2.0-85059156893 (Scopus ID)
Note

QC 20190320

Available from: 2019-03-20 Created: 2019-03-20 Last updated: 2019-03-20Bibliographically approved
Dogan, E., Örlü, R., Gatti, D., Vinuesa, R. & Schlatter, P. (2019). Quantification of amplitude modulation in wall-bounded turbulence. Paper presented at Inernational Camp-Style Seminar on Dynamics of Wall-Bounded Shear Flows, AUG 31-SEP 02, 2016, Kyoto, JAPAN. Fluid Dynamics Research, 51(1), Article ID 011408.
Open this publication in new window or tab >>Quantification of amplitude modulation in wall-bounded turbulence
Show others...
2019 (English)In: Fluid Dynamics Research, ISSN 0169-5983, E-ISSN 1873-7005, Vol. 51, no 1, article id 011408Article in journal (Refereed) Published
Abstract [en]

Many recent investigations on the scale interactions in wall-bounded turbulent flows focus on describing so-called amplitude modulation, the phenomenon that deals with the influence of large scales in the outer region on the amplitude of the small-scale fluctuations in the near-wall region. The present study revisits this phenomenon regarding two aspects, namely the method for decomposing the scales and the quantification of the modulation. First, the paper presents a summary of the literature that has dealt with either or both aspects. Second, for decomposing the scales, different spectral filters (temporal, spatial or both) and empirical mode decomposition (EMD) are evaluated and compared. The common data set is a well-resolved large-eddy simulation that offers a wide range of Reynolds numbers spanning Re-theta = 880-8200. The quantification of the amplitude modulation is discussed for the resulting scale components. Particular focus is given to evaluate the efficacy of the various filters to separate scales for the range of Reynolds numbers of interest. Different to previous studies, the different methods have been evaluated using the same data set, thereby allowing a fair comparison between the various approaches. It is observed that using a spectral filter in the spanwise direction is an effective approach to separate the small and large scales in the flow, even at comparably low Reynolds numbers, whereas filtering in time should be approached with caution in the low-to-moderate Re range. Additionally, using filters in both spanwise and time directions, which would separate both wide and long-living structures from the small and fast scales, gives a cleaner image for the small-scales although the contribution to the scales interaction from that filter implementation has been found negligible. Applying EMD to decompose the scales gives similar results to Fourier filters for the energy content of the scales and thereby for the quantification of the amplitude modulation using the decomposed scales. No direct advantage of EMD over classical Fourier filters could be seen. Potential issues regarding different decomposition methods and different definitions of the amplitude modulation are also discussed.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
amplitude modulation, turbulent boundary layer, scale interaction
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-243936 (URN)10.1088/1873-7005/aaca81 (DOI)000456203700009 ()2-s2.0-85061429605 (Scopus ID)
Conference
Inernational Camp-Style Seminar on Dynamics of Wall-Bounded Shear Flows, AUG 31-SEP 02, 2016, Kyoto, JAPAN
Note

QC 20190306

Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2019-03-18Bibliographically approved
Borodulin, V. I., Ivanov, A. V., Kachanov, Y. S., Mischenko, D. A., Örlü, R., Hanifi, A. & Hein, S. (2019). Receptivity coefficients of vortex-vibrational type at excitation of 3D Tollmien-Schlichting waves in a boundary layer on a swept wing. In: HIGH-ENERGY PROCESSES IN CONDENSED MATTER (HEPCM 2019): Proceedings of the XXVI Conference on High-Energy Processes in Condensed Matter, dedicated to the 150th anniversary of the birth of S.A. Chaplygin: . Paper presented at 26th All-Russian Conference on High Energy Processes in Condensed Matter: Dedicated to the 150th Anniversary of the Birth of S.A. Chaplygin, HEPCM 2019; Novosibirsk; Russian Federation; 3 April 2019 through 5 April 2019. American Institute of Physics (AIP), Article ID 030044.
Open this publication in new window or tab >>Receptivity coefficients of vortex-vibrational type at excitation of 3D Tollmien-Schlichting waves in a boundary layer on a swept wing
Show others...
2019 (English)In: HIGH-ENERGY PROCESSES IN CONDENSED MATTER (HEPCM 2019): Proceedings of the XXVI Conference on High-Energy Processes in Condensed Matter, dedicated to the 150th anniversary of the birth of S.A. Chaplygin, American Institute of Physics (AIP), 2019, article id 030044Conference paper, Published paper (Refereed)
Abstract [en]

The paper is devoted to the first results of an experimental quantitative study of the receptivity mechanism of a swept-wing laminar boundary layer related to scattering of 2D freestream vortices (with frequency fv) at 3D local surface vibrations (with frequency fs) resulting in an excitation of Tollmien-Schlichting (TS) waves (having combination frequencies f+ = fs+fv and f- = fs - fv). The experiments were carried out in a low-turbulence level wind tunnel on a high-precision experimental model of long-laminar-run swept airfoil (sweep angle of 35°) at a freestream speed of about 10 m/s. Controlled localized 3D surface vibrations and 2D freestream vortices were generated by special disturbance sources. Quantitative characteristics of the studied receptivity mechanism (receptivity coefficients) were estimated.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
Series
AIP Conference Proceedings, ISSN 0094-243X ; 2125
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-262562 (URN)10.1063/1.5117426 (DOI)2-s2.0-85070555367 (Scopus ID)9780735418653 (ISBN)
Conference
26th All-Russian Conference on High Energy Processes in Condensed Matter: Dedicated to the 150th Anniversary of the Birth of S.A. Chaplygin, HEPCM 2019; Novosibirsk; Russian Federation; 3 April 2019 through 5 April 2019
Note

QC 20191025

Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
Wang, Z., Örlü, R., Schlatter, P. & Chung, Y. M. (2018). Direct numerical simulation of a turbulent 90° bend pipe flow. International Journal of Heat and Fluid Flow, 73, 199-208
Open this publication in new window or tab >>Direct numerical simulation of a turbulent 90° bend pipe flow
2018 (English)In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 73, p. 199-208Article in journal (Refereed) Published
Abstract [en]

Direct numerical simulation (DNS) has been performed for a spatially developing 90° bend pipe flow to investigate the unsteady flow motions downstream of the bend. A recycling method is implemented to generate a fully-developed turbulent inflow condition. The Reynolds number of the pipe flow is ReD=5300 and the bend curvature is γ=0.4. A long straight pipe section (40D) is attached in the downstream of the bend to allow the flow to develop. Flow oscillations downstream of the bend are measured using several methods, and the corresponding oscillation frequencies are estimated. It is found that different characteristic frequencies are obtained from various flow measurements. The stagnation point movement and single-point velocity measurements may not be good measures to determine the swirl-switching frequency. The oscillations of the lateral pressure force on the pipe wall and half-sided mass flow rate are proposed to be a more unambiguous measure of the unsteady flow motions downstream of the bend. 

Place, publisher, year, edition, pages
Elsevier B.V., 2018
Keywords
90 degrees bend, Conditional averaging, Curved pipe, DNS, Swirl switching, Turbulent pipe flow, Direct numerical simulation, Flow rate, Numerical models, Pipe flow, Reynolds number, Turbulent flow, Characteristic frequencies, Curved pipes, Oscillation frequency, Stagnation points, Turbulent inflow conditions, Oscillating flow
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-236662 (URN)10.1016/j.ijheatfluidflow.2018.08.003 (DOI)000452345000017 ()2-s2.0-85052536769 (Scopus ID)
Note

Export Date: 22 October 2018; Article; CODEN: IJHFD; Correspondence Address: Chung, Y.M.; School of Engineering and Centre for Scientific Computing, University of WarwickUnited Kingdom; email: y.m.chung@warwick.ac.uk; Funding details: University of Warwick; Funding details: EP/L000261/1, EPSRC, Engineering and Physical Sciences Research Council; Funding text: This work has been supported by the Engineering and Physical Sciences Research Council grant no EP/L000261/1 . The authors would like to thank Professor Paul Fischer for the help in using Nek5000 . Simulations were performed on ARCHER, the UK National Supercomputing Service. This work also used the HPC facilities (Tinis) at the Centre for Scientific Computing, University of Warwick. QC 20181113

Available from: 2018-11-13 Created: 2018-11-13 Last updated: 2019-10-18Bibliographically approved
Borodulin, V. I., Ivanov, A. V., Kachanov, Y. S., Mischenko, D. A., Örlü, R., Hanifi, A. & Hein, S. (2018). Excitation of 3D TS-waves in a swept-wing boundary layer by surface vibrations and freestream vortices. In: AIP Conference Proceedings: . Paper presented at 19th International Conference on the Methods of Aerophysical Research, ICMAR 2018, 13 August 2018 through 19 August 2018. American Institute of Physics Inc.
Open this publication in new window or tab >>Excitation of 3D TS-waves in a swept-wing boundary layer by surface vibrations and freestream vortices
Show others...
2018 (English)In: AIP Conference Proceedings, American Institute of Physics Inc. , 2018Conference paper, Published paper (Refereed)
Abstract [en]

There are several kinds of velocity disturbances, which may affect the transition to turbulence in a swept wing boundary layer. Tollmien-Schlichting (TS) waves are among most important of them. The properties of TS waves and their potential competition with cross-flow waves on a swept wing are poorly studied in theoretical works and were not studied experimentally at all. This paper presents the method of excitation of fully controlled 3D TS waves via interaction of free-stream vortices and surface vibrations. The experimental approach developed here will be used for investigation of the corresponding receptivity problem.

Place, publisher, year, edition, pages
American Institute of Physics Inc., 2018
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-247077 (URN)10.1063/1.5065230 (DOI)000481675800152 ()2-s2.0-85056347707 (Scopus ID)9780735417472 (ISBN)
Conference
19th International Conference on the Methods of Aerophysical Research, ICMAR 2018, 13 August 2018 through 19 August 2018
Note

QC 20190503

Available from: 2019-05-03 Created: 2019-05-03 Last updated: 2019-09-05Bibliographically approved
Vernet, J. A., Örlü, R. & Alfredsson, P. H. (2018). Flow separation control by dielectric barrier discharge plasma actuation via pulsed momentum injection. AIP Advances, 8(7), Article ID 075229.
Open this publication in new window or tab >>Flow separation control by dielectric barrier discharge plasma actuation via pulsed momentum injection
2018 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 7, article id 075229Article in journal (Refereed) Published
Abstract [en]

Control of a turbulent boundary layer separating on a half-cylinder mounted on a flat plate has been investigated using a Dielectric Barrier Discharge (DBD) plasma actuator placed along the apex of a cylinder. The main focus of the study has been to evaluate if the control ability of the actuator can be improved through pulsed actuation compared to its steady counterpart. Investigations of the electric wind induced by the DBD plasma actuator in still air, when mounted on the flat plate, revealed that while the steady actuation produces an electric wind similar to a wall jet, the pulsed actuation creates a train of co-rotating vortices. The vortices are the result of a starting vortex produced by the actuator at each actuation pulse. A parametric study showed a dependence of the size, shape and propagation velocity of the vortices on the pulse frequency and duty cycle. With the actuator mounted along the apex of the cylinder, Particle Image Velocimetry measurements of the uncontrolled and controlled flow with a free-stream velocity of 5 m/s showed a clear reduction of the recirculation region downstream the cylinder when using plasma actuation. An even higher control effect could be achieved with pulsed actuation compared to the steady actuation. Phase-locked measurements of the unsteady actuation showed that pulsed actuation periodically shifted the flow separation location resulting in the propagation of vortical structures in the recirculation region. The size of the vortical structures showed a dependence on the pulsed actuation timing parameters.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
Keywords
Turbulent-Boundary-Layer, Vortex Generators
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-233426 (URN)10.1063/1.5037770 (DOI)000440602300090 ()2-s2.0-85050998450 (Scopus ID)
Funder
Swedish Energy Agency, 34186-1Swedish Foundation for Strategic Research
Note

QC 20180821

Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-08-21Bibliographically approved
Chin, C., Vinuesa, R., Örlü, R., Cardesa, J. I., Noorani, A., Schlatter, P. & Chong, M. S. (2018). Flow topology of rare back flow events and critical points in turbulent channels and toroidal pipes. In: Journal of Physics: Conference Series. Paper presented at 3rd Madrid Summer School on Turbulence, School of Aeronautics of the Universidad Politecnica de MadridMadrid, Spain, 29 May 2017 through 30 June 2017. Institute of Physics Publishing (IOPP), 1001(1), Article ID 012002.
Open this publication in new window or tab >>Flow topology of rare back flow events and critical points in turbulent channels and toroidal pipes
Show others...
2018 (English)In: Journal of Physics: Conference Series, Institute of Physics Publishing (IOPP), 2018, Vol. 1001, no 1, article id 012002Conference paper, Published paper (Refereed)
Abstract [en]

A study of the back flow events and critical points in the flow through a toroidal pipe at friction Reynolds number Reτ ≈ 650 is performed and compared with the results in a turbulent channel flow at Reτ ≈ 934. The statistics and topological properties of the back flow events are analysed and discussed. Conditionally-averaged flow fields in the vicinity of the back flow event are obtained, and the results for the torus show a similar streamwise wall-shear stress topology which varies considerably for the spanwise wall-shear stress when compared to the channel flow. The comparison between the toroidal pipe and channel flows also shows fewer back flow events and critical points in the torus. This cannot be solely attributed to differences in Reynolds number, but is a clear effect of the secondary flow present in the toroidal pipe. A possible mechanism is the effect of the secondary flow present in the torus, which convects momentum from the inner to the outer bend through the core of the pipe, and back from the outer to the inner bend through the pipe walls. In the region around the critical points, the skin-friction streamlines and vorticity lines exhibit similar flow characteristics with a node and saddle pair for both flows. These results indicate that back flow events and critical points are genuine features of wall-bounded turbulence, and are not artifacts of specific boundary or inflow conditions in simulations and/or measurement uncertainties in experiments.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
Series
Journal of Physics: Conference Series, ISSN 1742-6588 ; 1001
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-238246 (URN)10.1088/1742-6596/1001/1/012002 (DOI)000454926900002 ()2-s2.0-85046100946 (Scopus ID)
Conference
3rd Madrid Summer School on Turbulence, School of Aeronautics of the Universidad Politecnica de MadridMadrid, Spain, 29 May 2017 through 30 June 2017
Note

QC 20181101

Available from: 2018-11-01 Created: 2018-11-01 Last updated: 2019-01-18Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1663-3553

Search in DiVA

Show all publications