Introduction of background knowledge regarding flow physics and CFD as well as detailed information about the use of AcuSolve and what specific options do.
Collection of AcuSolve simulation cases for which results are compared against analytical or experimental results to demonstrate the accuracy
of AcuSolve results.
In this application, AcuSolve is used to simulate the wall heat flux due to nucleate boiling at a heated wall inside a rectangular channel with
water flow. Results are compared with experimental heat flux measurements as reported by Steiner, et al. (2005). The
close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model single phase nucleate boiling problems.
In this application, turbulent flow of air through a pipe is simulated. AcuSolve results are compared with experimental results as described in White (1991) and extracted from the Moody chart. The
close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model turbulent flow within pipes.
In this application, AcuSolve is used to simulate turbulent flow of air through and behind a two dimensional open-slit V. AcuSolve results are compared with experimental results adapted from Yang and Tsai (1993). The close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model the Coandă effect.
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.
In this application, AcuSolve is used to simulate fully developed turbulent flow over a backward-facing step. AcuSolve results are compared with experimental results as described in Driver (1985) and on the NASA Langley Research
Center Turbulence Modeling Resource web page. The close agreement of AcuSolve results with experimental data and reference turbulence model performance validates the ability of AcuSolve to model cases with turbulent flow that forms a shear layer, recirculates and then reattaches downstream
of the divergent step.
In this application, AcuSolve is used to simulate fully developed turbulent flow through an axisymmetric diffuser with a divergent upper wall and
a straight lower wall. AcuSolve results are compared with experimental results as described in Driver (1991) and on the NASA Langley Research Center
Turbulence Modeling Resource webpage. The close agreement of AcuSolve results with experimental data and reference turbulence model performance validates the ability of AcuSolve to model cases with turbulent flow with separation due to an adverse pressure gradient within an axisymmetric
geometry.
In this application, AcuSolve is used to simulate fully developed turbulent flow through a channel containing a convex curve in the lower wall.
AcuSolve results are compared with experimental results as described in Smits (1979) and on the NASA Langley Research Center
Turbulence Modeling Resource webpage. The close agreement of AcuSolve results with experimental data and reference turbulence model performance validates the ability of AcuSolve to model cases with turbulent flow moving past a convex curved wall.
In this application, AcuSolve is used to simulate the natural convection of a turbulent flow field within a tall rectangular cavity. AcuSolve results are compared with experimental results as described in Betts and Bokhari (2000). The close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model cases with natural convection of turbulent flow within a tall cavity.
In this application, AcuSolve is used to simulate turbulent flow of a fluid over a NACA 0012 airfoil at 3 angles of attack, 0 degrees, 10
degrees, and 15 degrees. AcuSolve results are compared with experimental results for coefficients of pressure, lift, and drag reported by NASA. The
close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model external aerodynamics.
In this application, AcuSolve is used to simulate turbulent flow through a strongly curved two dimensional 180 degree U-duct channel. AcuSolve results are compared with experimental results adapted from Rumsey et al. (2000). The close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model turbulent cases with strong curvature effects.
In this application, AcuSolve is used to simulate turbulent flow through a channel with a lower wall shaped as a sinusoidal wave. AcuSolve results are compared with experimental results adapted from Kuzan (1986). The close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model cases with internal flow through a channel with wavy walls.
In this application, AcuSolve is used to solve for the flow and temperature field within a channel containing a heated wall. The wall is maintained
at a constant temperature, inducing heat flux into the fluid, to predict the thermal law of the wall. The non-dimensional
temperature versus the non-dimensional height above the wall is compared to the analytical correlation provided by
Kader.
In this application, AcuSolve is used to simulate the mixing of two streams of fluid with different velocities moving past a splitter plate.
AcuSolve results are compared with experimental results as described in J. Delville, et al. (1989). The close agreement of
AcuSolve results with the experimental results validates the ability of AcuSolve to model mixing layers in the turbulent flow regime.
In this application, AcuSolve is used to simulate the changes in wall temperature due to two-phase nucleate boiling at the heated walls of a pipe
with water flowing through it. AcuSolve results are compared with experimental results adapted from Koncar and others (2015). The close agreement of
AcuSolve results with experimental results validates the ability of AcuSolve to model two-phase nucleate boiling problems.
In this application, AcuSolve is used to simulate the high-speed turbulent flow in a converging and then diverging nozzle. The flow within the
nozzle enters as subsonic, reaches sonic at the throat and shortly after develops a normal shock. AcuSolve results are compared with experimental results adapted from Bogar and Sajben (1983). The close agreement of AcuSolve results to experimental measurements validates the ability of AcuSolve to simulate internal supersonic flows where normal shocks are present.
In this application, AcuSolve is used to simulate fully developed turbulent flow past a smooth hump on the lower wall of a flow domain. AcuSolve results are compared with experimental results as described in Seifert and Pack (2002) and on the NASA Langley Research
Center Turbulence Modeling Resource web page. The close agreement of AcuSolve results with experimental data and reference turbulence model performance validates the ability of AcuSolve to model cases with turbulent flow moving past a wall protrusion resulting in flow separation and recovery.
In this application, AcuSolve is used to simulate the fluid-structure interaction of a fluid moving over a cylinder/plate assembly. AcuSolve results are compared with experimental results as described in Gomes and Lienhart (2009). The close agreement of
AcuSolve results with the experimental results validates the ability of AcuSolve to model cases in which the fluid forces lead to structural motions.
This section includes validation cases that consider unbounded simulation domains where external flow is present over
solid bodies, leading to free boundary layer development.
This section includes validation cases containing conditions producing laminar to turbulent flow that are simulated
with a turbulence transition model.
This section includes validation cases that consider time dependent motion within the domain, requiring that the mesh
movement be modeled with a differential equation, a fully defined mesh motion or by interpolated mesh motion.
Collection of AcuSolve simulation cases for which results are compared against analytical or experimental results to demonstrate the accuracy
of AcuSolve results.
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.
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
The problem consists of air flowing through an asymmetric diffuser with a divergent lower wall
and a straight upper wall, as shown in the following image, which is not drawn to
scale. The diffuser inlet has a height of 1.5 cm (H) and extends 9 cm (6H) to the
divergent section. The lower wall of the diffuser diverges at an angle of 10° and
expands to 7.05 cm (4.7H). The divergent section has a horizontal length of 31.5 cm
(21H). The expanded section of the diffuser extends 84 cm (56H) to the outlet. Air,
with a density of 1.225 kg/m3 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.
The simulation was performed as a two dimensional problem by constructing a volume mesh that
contains a single layer of elements extruded in the cross stream direction
(perpendicular to the flow plane) and by imposing symmetry boundary conditions on
the extruded planes.
AcuSolve Results
The AcuSolve solution converged to a steady state and the results
reflect the mean flow conditions. As the fully developed turbulent flow enters the
divergent section, the peak velocity is maintained until the expansion of the
cross-sectional height, forms an adverse pressure gradient. After the flow enters
the divergent section, the velocity decreases significantly, due to the expansion of
the cross-section height. This causes separation of the flow along the divergent
wall and results in an area of recirculation. The bulk of the flow above the
divergent wall maintains its streamwise direction, while a portion of it reverses
direction before reattaching further downstream of the divergent section. The
following images show the steady state flow solution for flow within the
diffuser.
Upstream of the diffuser section, the streamline velocity increases as the distance from the
lower wall increases until it reaches the maximum velocity at the center of the
channel. As the flow enters the divergent section of the channel, the streamwise
velocity decreases near the bottom wall. The images below show the velocity profiles
at three locations as measured from the midpoint of the curve where the bottom wall
begins to diverge (X=0.0) for each of the tested turbulence models. The first
location, where X/H = -5.944, is close to the inlet. The second location, where X/H
= 13.468, is approximately 0.2 m downstream of the divergent section (~ 0.1 m from
the fully expanded section). The third location, where X/H = 24.066, is
approximately 0.16 m downstream of the point where the diffuser has reached the
maximum height. In these plots the black circles represent the experimental
measurements (Buice and Eaton 2000), the solid red lines for the prediction for the
Spalart Allmaras model, solid blue lines for the prediction for the SST model, solid
green lines for the prediction for the K-ω model and solid cyan lines for the K-ε
model, representing the AcuSolve results. The
non-dimensional height is represented by the fraction of the vertical height (Y)
divided by the inlet height (H) and the velocity is normalized by the inlet velocity
(Uref).
The non-dimensional pressure coefficient (Cp) all along the inlet-bottom stretch of the diffuser
is calculated using the reference pressure at X=-3H (at the bottom wall) and with
reference velocity (Uref) at the inlet with the value of 22.3152 (m/s). The
predicted non-dimensional pressure coefficients are compared to experimental
results. The figure below shows Cp, along a constant vertical height, as a function
of the streamwise distance from the inlet of the channel. The results demonstrate
that AcuSolve is capable of accurately predicting the
pressure within the diffuser within the expected range based on the type of
turbulence model used. The performance of the three turbulence models were found to
be consistent with previously published results for flow through the diffuser as
published by Buice and Eaton (2000), with the SST model predicting the pressure
distribution most accurately.
Note: The inlet of the experimental duct was 6H longer
than that modeled - AcuSolve values where X/H <
-6 are reported as the inlet value.
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
HyperWorks 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
Material Model
Air
Density - 1.225.0 kg/m3
Viscosity - 1.8325e-5 kg/m-sec
Model
Volume
Volume
Element Set
Material model - Air
Surfaces
Bottom
Simple Boundary Condition
Type - Wall
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)
Outlet
Simple Boundary Condition
Type - Outflow - 101139.0 Pa
Side 1
Simple Boundary Condition
Type - Symmetry
Side 2
Simple Boundary Condition
Type - Symmetry
Top
Simple Boundary Condition
Type - Wall
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.