UFR 4-16 Description: Difference between revisions
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large majority of the experimental benchmarks being used for validating | large majority of the experimental benchmarks being used for validating | ||
computational methods and turbulence models relate to two-dimensional | 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 | internal flow configurations, e.g. the flow in a 2-D diffuser (e.g. Obi ''et al.'', 1993), | ||
al., 1993), flow over a backward-facing step and a forward-facing step, or | 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 | 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 | of a plane channel. In these examples it is assumed that the influence of | ||
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nature of the flow is completely missed: considerable secondary | nature of the flow is completely missed: considerable secondary | ||
motion across the inlet section of the channel induced by the Reynolds | motion across the inlet section of the channel induced by the Reynolds | ||
stress anisotropy | stress anisotropy — which is, as generally known, beyond the reach of the | ||
eddy-viscosity RANS model group, complex 3-D separation patterns spreading | eddy-viscosity RANS model group, complex 3-D separation patterns spreading | ||
over duct corners (corner separation and corner reattachment), etc. | over duct corners (corner separation and corner reattachment), etc. | ||
These circumstances were the prime motivation for the recent experimental | These circumstances were the prime motivation for the recent experimental | ||
study of the flow in a three-dimensional diffuser conducted by Cherry et | study of the flow in a three-dimensional diffuser conducted by Cherry ''et al.'' (2008, 2009). | ||
al. (2008, 2009). Such a diffuser configuration is also of a high practical | Such a diffuser configuration is also of a high practical | ||
relevance. It mimics a diffuser situated between a compressor and the | relevance. It mimics a diffuser situated between a compressor and the | ||
combustor chamber in a jet engine. Its task is to decelerate the flow | combustor chamber in a jet engine. Its task is to decelerate the flow | ||
Revision as of 11:23, 25 July 2012
Flow in a 3D diffuser
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
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| Figure 2: Detailed diffuser design: geometry and dimensions. From Cherry et al. (2009) |
Contributed by: Suad Jakirlić — Technische Universität Darmstadt
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