Hostname: page-component-5d59c44645-ndqjc Total loading time: 0 Render date: 2024-02-28T23:52:55.276Z Has data issue: false hasContentIssue false

The separating flow in a plane asymmetric diffuser with 8.5° opening angle: mean flow and turbulence statistics, temporal behaviour and flow structures

Published online by Cambridge University Press:  25 September 2009

OLLE TÖRNBLOM*
Affiliation:
KTH Mechanics, SE-100 44 Stockholm, Sweden
BJÖRN LINDGREN
Affiliation:
KTH Mechanics, SE-100 44 Stockholm, Sweden
ARNE V. JOHANSSON
Affiliation:
KTH Mechanics, SE-100 44 Stockholm, Sweden
*
Email address for correspondence: olle@mech.kth.se

Abstract

The flow in a plane asymmetric diffuser with an opening angle of 8.5° has been studied experimentally using time-resolving stereoscopic particle image velocimetry. The inlet condition is fully developed turbulent channel flow at a Reynolds number based on the inlet channel height and bulk velocity of Re = 38000. All mean velocity and Reynolds stress components have been measured. A separated region is found on the inclined wall with a mean separation point at 7.4 and a mean reattachment point at 30.5 inlet channel heights downstream the diffuser inlet (the inclined wall ends 24.8 channel heights downstream the inlet). Instantaneous flow reversal never occurs upstream of five inlet channel heights but may occur far downstream the point of reattachment. A strong shear layer in which high rates of turbulence production are found is located in a region outside the separation. The static wall pressure through the diffuser is presented and used in an analysis of the balance between pressure forces and momentum change. It is demonstrated that production of turbulence causes a major part of the losses of mean flow kinetic energy. The character of the large turbulence structures is investigated by means of time-resolved sequences of velocity fields and spatial auto-correlation functions. Pronounced inclined structures are observed in the spanwise velocity and it is suggested that these are due to the legs of hairpin-like vortices.

Type
Papers
Copyright
Copyright © Cambridge University Press 2009

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Footnotes

Present address: Studsvik Nuclear AB, SE-611 82, Nyköping, Sweden

Present address: Scania CV AB, SE-151 87, Södertälje, Sweden

References

REFERENCES

Adrian, R. J., Christensen, K. T. & Liu, Z.-C. 2000 a Analysis and interpretation of instantaneous turbulent velocity fields. Exp. Fluids 29, 275290.Google Scholar
Adrian, R. J., Meinhart, C. D. & Tomkins, C. D. 2000 b Vortex organization in the outer region of the turbulent boundary layer. J. Fluid Mech. 422, 154.Google Scholar
Brüger, A., Nilsson, J., Kress, W., Stålberg, E., Gustafsson, B., Lötstedt, P., Johansson, A. V. & Henningson, D. S. 2004 A hybrid high order method for incompressible flow in complex geometries. Tech. Rep. TRITA-MEK 2004:11. KTH Mechanics.Google Scholar
Buice, C. U. & Eaton, J. K. 1997 Experimental investigation of flow through an asymmetric plane diffuser. Tech. Rep. Department of Mechanical Engineering, Stanford university.Google Scholar
Buice, C. U. & Eaton, J. K. 2000 Experimental investigation of flow through an asymmetric plane diffuser. J. Fluids Engng 122, 433435.Google Scholar
Comte-Bellot, G. 1965 Écoulement turbulent entre deux paroix parallèles. Publications scientifiques et techniques 419. Ministère de l'air, 2, Avenue de la Porte-d'Issy, Paris.Google Scholar
van Doorne, C. W. H. 2004 Stereoscopic PIV on transition in pipe flow. PhD thesis, Technische Universiteit Delft.Google Scholar
Foucaut, J., Carlier, J. & Stanislas, M. 2004 PIV optimization for the study of turbulent flow using spectral analysis. Meas. Sci. Technol. 15, 10461058.Google Scholar
Gullman-Strand, J. 2004 Turbulence and scalar flux modelling applied to separated flows. PhD thesis, KTH Mechanics, Stockholm, Sweden.Google Scholar
Gullman-Strand, J., Törnblom, O., Lindgren, B., Amberg, G. & Johansson, A. V. 2004 Numerical and experimental study of separated flow in a plane asymmetric diffuser. Intl J. Heat Fluid Flow 25, 451460.Google Scholar
Hellsten, A. & Rautaheimo, P. (Ed.) 1999 Workshop on Refined Turbulence Modelling. ERCOFTAC/IAHR/COST.Google Scholar
Herbst, A. H. 2006 Numerical studies of turbulent and separated flows. PhD thesis, KTH Mechanics, Stockholm, Sweden.Google Scholar
Johansson, A. V. & Alfredsson, P. H. 1981 Development of a water tunnel for studies of turbulent shear flows. Tech. Rep. TRITA-MEK-81-01. Royal Institute of Technology.Google Scholar
Kaltenbach, H.-J., Fatica, M., Mittal, R., Lund, T. S. & Moin, P. 1999 Study of flow in a planar asymmetric diffuser using large-eddy simulation. J. Fluid Mech. 390, 151185.Google Scholar
Keane, R. & Adrian, R. 1992 Theory of cross-correlation in PIV. Appl. Sci. Res. 49, 191215.Google Scholar
Keane, R. D. & Adrian, R. J. 1990 Optimization of particle image velocimeters. Part I. double pulsed systems. Meas. Sci. Technol. 1, 12021215.Google Scholar
Krogstad, P.-Å. & Antonia, R. A. 1994 Structure of turbulent boundary layers on smooth and rough walls. J. Fluid Mech. 277, 121.Google Scholar
Le, H., Moin, P. & Kim, J. 1997 Direct numerical simulation of turbulent flow over a backward-facing step. J. Fluid Mech. 330, 349374.Google Scholar
Obi, S., Aoki, K. & Masuda, S. 1993 a Experimental and computational study of turbulent separating flow in an asymmetric plane diffuser. In Ninth Symp. on Turbulent Shear Flows, Kyoto, Japan.Google Scholar
Obi, S., Ishibashi, N. & Masuda, S. 1997 The mechanism of momentum transfer enhancement in periodically perturbed turbulent separated flow. In Second Intl Symp. on Turbulence, Heat and Mass Transfer, pp. 835844. Delft, The Netherlands.Google Scholar
Obi, S., Nikaido, H. & Masuda, S. 1999 Reynold number effect on the turbulent separating flow in an asymmetric plane diffuser. In Proc. FEDSM99, FEDSM 99-6976 (ASME/JSME Fluids Engineering Division Summer Meeting).Google Scholar
Obi, S., Ohizumi, K., Aoki, K. & Masuda, S. 1993 b Turbulent separation control in a plane asymmetric diffuser by periodic perturbation. In Engineering Turbulence Modelling and Experiments 2, pp. 633642. Elsevier.Google Scholar
Raffel, M., Willert, C. & Kompenhans, J. 1997 Particle Image Velocimetry, A Practical Guide. Springer.Google Scholar
Scarano, F. & Riethmuller, M. L. 2000 Advances in iterative multigrid PIV image processing. Exp. Fluids 29 (Suppl.), S51S60.Google Scholar
Simpson, R. L. 1989 Turbulent boundary-layer separation. Ann. Rev. Fluid Mech. 21, 205234.Google Scholar
Song, S. & Eaton, J. K. 2004 Flow structures of a separating, reattaching and recovering boundary layer for a large range of Reynolds number. Exp. Fluids 36, 642653.Google Scholar
Törnblom, O. 2006 Experimental and computational studies of turbulent separating internal flows. PhD thesis, KTH Mechanics, Stockholm, Sweden.Google Scholar
Westerweel, J. 1997 Fundamentals of digital particle image velocimetry. Meas. Sci. Technol. 8, 13791392.Google Scholar
Wieneke, B. 2005 Stereo-PIV using self-calibration on particle images. Exp. Fluids 39, 267280.Google Scholar
Wu, X., Schlüter, J., Moin, P., Pitsch, H., Iaccarino, G. & Ham, F. 2006 Computational study on the internal layer in a diffuser. J. Fluid Mech. 550, 391412.Google Scholar