UFR 4-16 Description: Difference between revisions

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of a plane channel. In these examples it is assumed that  the  influence  of
of a plane channel. In these examples it is assumed that  the  influence  of
the side walls (according to  
the side walls (according to  
[[YFR_4-16_references#2|Bradshaw and Wong, 1972]],
[[UFR_4-16_References#2|Bradshaw and Wong, 1972]],
the  minimum  aspect
the  minimum  aspect
ratio — representing the ratio of the channel  height  to  channel  width  —
ratio — representing the ratio of the channel  height  to  channel  width  —

Revision as of 08:18, 26 July 2012

Flow in a 3D diffuser

Front Page

Description

Test Case Studies

Evaluation

Best Practice Advice

References

Confined flows

Underlying Flow Regime 4-16

Description

Introduction/motivation

Configurations involving three-dimensional boundary-layer separation are among the most frequently encountered flow geometries in practice. Accordingly, the methods for simulating them have to be appropriately validated using detailed and reliable reference databases. However, the large majority of the experimental benchmarks being used for validating computational methods and turbulence models relate to two-dimensional internal flow configurations, e.g. the flow in a 2-D diffuser (e.g. Obi et al., 1993), flow over a backward-facing step and a forward-facing step, or flow over fences, ribs, 2-D hills and 2-D humps mounted on the bottom wall of a plane channel. In these examples it is assumed that the influence of the side walls (according to Bradshaw and Wong, 1972, the minimum aspect ratio — representing the ratio of the channel height to channel width — should be 1:10 in order to eliminate the influence of the side walls) is not felt at the channel midplane. Consequently, within a computational framework, the spanwise direction can be regarded as homogeneous which allows the application of periodic boundary conditions (even 2D computations when using the RANS approach). By doing so, the three‐dimensional nature of the flow is completely missed: considerable secondary motion across the inlet section of the channel induced by the Reynolds stress anisotropy — which is, as generally known, beyond the reach of the eddy-viscosity RANS model group, complex 3-D separation patterns spreading over duct corners (corner separation and corner reattachment), etc.

These circumstances were the prime motivation for the recent experimental study of the flow in a three-dimensional diffuser conducted by Cherry et al. (2008, 2009). Such a diffuser configuration is also of a high practical relevance. It mimics a diffuser situated between a compressor and the combustor chamber in a jet engine. Its task is to decelerate the flow discharging from compressor over a very short distance to the velocity field of the combustor section. Typically a uniform inlet profile over the diffuser outlet is desirable. Such a flow situation is associated by a strong pressure increase.

Review of UFR studies and choice of test case

UFR4-16 figure2.png
Figure 2: Detailed diffuser design: geometry and dimensions. From Cherry et al. (2009)




Contributed by: Suad Jakirlić — Technische Universität Darmstadt

Front Page

Description

Test Case Studies

Evaluation

Best Practice Advice

References


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