# Turbulent Flow with Separation in an Asymmetric Diffuser

In this application, AcuSolve is used to simulate fully developed turbulent flow through an asymmetric diffuser with a divergent lower wall and a straight upper wall. AcuSolve results are compared with experimental results as described in Buice and Eaton (2000). The close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model cases with internal turbulent flow with flow separation and reattachment in an asymmetric diffuser.

## Problem Description

^{3}and a viscosity of 1.8325 X 10

^{-5}kg/m-s enters the diffuser through the inlet of the diffuser with a fully developed turbulent profile at a Reynolds's number of 20,000. The simulation was conducted with the Reynolds Averaged Navier-Stokes equations using four turbulence models, Spalart Allmaras, Shear Stress Transport (SST), K-ω and Realizable K-ε.

## AcuSolve Results

## Summary

In this application, a fully developed turbulent flow at a Reynolds number of 20,000 is studied. Due to the adverse pressure gradient, separation of flow occurs and causes recirculation in the divergent section of the diffuser. The results were found to be consistent with previously published computational studies and experimental data. The results of this validation demonstrate the ability of AcuSolve to accurately predict the separation point, the recirculation that occurs along the divergent wall, and the reattachment point in the straight section of the diffuser.

## Simulation Settings for Turbulent Flow with Separation in an Asymmetric Diffuser

HyperMesh CFD database file: <your working directory>\asymmetric_diffuser_turbulent\asymmetric_diffuser_turbulent.hm

Global

- Problem Description
- Analysis type - Steady State
- Turbulence equation - Spalart Allmaras

- Auto Solution Strategy
- Max time steps -
`150` - Relaxation Factor -
`0.4`

- Max time steps -
- Material Model
- Air
- Density -
`1.225.0`kg/m3 - Viscosity -
`1.8325e-5`kg/m-sec

- Density -

Model

- Air
- Volume
- Volume
- Element Set
- Material model - Air

- Element Set

- Volume
- Surfaces
- Bottom
- Simple Boundary Condition
- Type - Wall

- Simple Boundary Condition
- Inlet
- Simple Boundary Condition (disabled to allow for nodal boundary conditions to be set)
- Advanced Options
- Nodal Boundary Conditions
- X-Velocity
- Type - Linear
- Precedence -
`2` - Curve fit variable - Y coordinate
- Curve fit values (included in database)

- Y-Velocity
- Type - Linear
- Precedence -
`2` - Curve fit variable - Y coordinate
- Curve fit values (included in database)

- Eddy Viscosity
- Type - Linear
- Precedence -
`2` - Curve fit variable - Y coordinate
- Curve fit values (included in database)

- X-Velocity

- Nodal Boundary Conditions

- Outlet
- Simple Boundary Condition
- Type - Outflow - 101139.0 Pa

- Simple Boundary Condition
- Side 1
- Simple Boundary Condition
- Type - Symmetry

- Simple Boundary Condition
- Side 2
- Simple Boundary Condition
- Type - Symmetry

- Simple Boundary Condition
- Top
- Simple Boundary Condition
- Type - Wall

- Simple Boundary Condition

- Bottom

## References

C.U. Buice, and J.K., Eaton. "Experimental Investigation of Flow Through an Asymmetric Plane Diffuser". Journal of Fluids Engineering 122:433-435. June 2000.

S. Obi, K. Aoki and S. Masuda. "Experimental and Computational Study of Turbulent Separating Flow in an Asymmetric Plane Diffuser". Ninth Symposium on Turbulent Shear Flows. p. 305. Kyoto, Japan. August 16-19, 1993.