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 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.
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 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.
Turbulent Flow with Separation in an Axisymmetric Diffuser
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.
Problem Description
The problem consists of a fluid with material properties close to air flowing around a cylinder
through an axisymmetric diffuser, as shown in the following image, which is not
drawn to scale. The diffuser has a divergent section designed to generate an adverse
pressure gradient. The inlet height between the cylinder and the upper section of
the diffuser is 0.0355 m. The diffuser is constructed such that the section is
axisymmetric around a cylinder with a diameter of 0.14 m. The inflow of the diffuser
is set to produce a fully developed turbulent flow profile at a Reynolds number (Re)
of 2,000,000. The upper section is modeled with a slip boundary condition, in order
to match experimental conditions. The density of the fluid is 1.0 kg/m3
and with a dynamic viscosity of 1.5 X 10-5 kg/m-s. 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 problem is simulated as axisymmetric by considering a 1 degree portion of the diffuser with
the axisymmetric boundary condition applied on the cross-stream surfaces. The mesh
elements were extruded in the axisymmetric direction to create a mesh with two
elements spanning the simulated section.
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 expansion of the cross-sectional height causes the streamwise
velocity to decrease. This causes separation of the flow along the cylinder wall and
results in an area of recirculation that eventually recovers downstream. After the
flow enters the diffuser, the velocity decreases significantly from the inlet
velocity, due to the rapid expansion of the cross section height in the divergent
section. A separation bubble forms within the diffuser, with decreased flow velocity
and increased pressure near the lower wall.
Upstream of the diffuser section, the streamwise velocity increases as the distance from the
cylinder wall increases, with no influence from the top wall of the diffuser. As the
flow enters into the divergent section, the streamwise velocity decreases near the
cylinder wall and changes direction in the recirculation region. Within the
recirculation region, the reduced speed of the streamwise flow causes the wall shear
stress to decrease and eventually change direction for a short distance along the
cylinder surface. The images below show the coefficient of pressure (Cp) and
coefficient of skin friction (Cf) along the cylinder wall in the diffuser compared
against experimental results. The non-dimensional values are defined by the
integrated inlet pressure and the magnitude of the inlet velocity. In the images
black circles represent the experimental measurements (Driver 1991), solid red lines
represent the prediction for the SA model, solid blue lines represent the prediction
for the SST model, solid green lines represent the prediction for the K-ω model and
solid cyan lines for the K-ε model, representing the AcuSolve results. There are minor differences in the
prediction of the pressure coefficient within the diffuser between the three
turbulence models. The SA model predicts a slightly higher value of pressure as the
flow separates from the cylinder wall compared to both SST and K- ω. The shearing on
the cylinder wall shows similar behavior, with the SA model predicting a slightly
longer recirculation region and with the K- ω model predicting the separation
further upstream. It was found that all three turbulence models predict the
separation point further upstream than what is shown in the experiment. This is
shown to be consistent with previous studies for each of the turbulence models used
(NASA 2014).
Summary
In this application, a fully developed turbulent flow at a Reynolds number of 2,000,000 is studied and compared against experimental data. The
AcuSolve results compare well with the experimental data for pressure coefficient and skin friction coefficient. The recirculation region is slightly over predicted by the turbulence models studied, but the results still show a reasonable trend compared to experimental results. The performance of the three turbulence models was found to be consistent with previously published results for flow within an axisymmetric diffuser (NASA 2014). The results of this validation demonstrate the ability of
AcuSolve to accurately predict flow recirculation with axisymmetric boundary conditions.
Simulation Settings for Turbulent Flow with Separation in an Axisymmetric
Diffuser
AcuConsole database file: <your working
directory>\axisymmetric_diffuser_turbulent\axisymmetric_diffuser_turbulent.acs
Global
Problem Description
Analysis type - Steady State
Turbulence equation - Spalart Allmaras
Auto Solution Strategy
Max time steps - 150
Relaxation Factor - 0.4
Material Model
Fluid
Density - 1.0 kg/m3
Viscosity - 1.5e-5 kg/m-sec
Model
Volume
Fluid
Element Set
Material model - Fluid
Surfaces
Axisymmetric_maxZ
Simple Boundary Condition - (disabled to allow for periodic
conditions to be set)
Axisymmetric_minZ
Simple Boundary Condition - (disabled to allow for periodic
conditions to be set)
Inlet
Simple Boundary Condition
Type - Inflow
Inflow type - Velocity
X velocity - 30.0 m/sec
Turbulence input type - Direct
Eddy viscosity - 1.5e-5
m2/sec
Outlet
Simple Boundary Condition
Type - Outflow
Slip_maxY
Simple Boundary Condition
Type - Slip
Wall_minY
Simple Boundary Condition
Type - Wall
Periodics
Axisymmetric
Periodic Boundary Condition
Type - Axisymmetric
Rotation Axis
Point 1
x-coordinate - 1.4
m
y-coordinate - 0.0
m
z-coordinate - 0.0
m
Point 2
x-coordinate - -1.5
m
y-coordinate - 0.0
m
z-coordinate - 0.0
m
References
D. M. Driver. "Reynolds Shear Stress Measurements in a Separated Boundary Layer
Flow". AIAA Paper 91-1787 from the AIAA 22nd Fluid Dynamics, Plasma Dynamics,
and Lasers Conference. Honolulu, HI. June 1991.
NASA Langley Research Center Turbulence Modeling Resource webpage,
http://turbmodels.larc.nasa.gov/driver_val.html. Accessed December
2014.