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, 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 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 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 (1996). 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 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 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 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.
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 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 water and the time-dependent interface of air-water within a tank subject to a prescribed sloshing
motion. AcuSolve results are compared with experimental pressure measurements as reported by Tankaka, et al. (2000) and Rhee (2005).
The close agreement of AcuSolve results with experimental results validates the ability of AcuSolve to model multiphase flow problems with user-defined motion.
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 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 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.
Problem Description
The problem consists of a fluid with material properties close to air flowing through a channel
containing a 30° swept wall, with a lower convex wall. The inlet channel height and
remaining duct height is 0.127 m. The bulk velocity (v) normal to the inlet is 31.9
m/s and an integrated outflow pressure is specified to allow the flow to pass
through the channel. The flow develops into fully turbulent flow at a Reynolds's
number (Re) of 2,100,000. The density of the flow medium is 1.225 kg/m3 and the
dynamic viscosity is 1.8608 X 10-5 kg/m-s. The simulation is conducted with the
Reynolds Averaged Navier-Stokes equations using the Spalart Allmaras, Shear Stress
Transport (SST), K-ω and Realizable K-ε turbulence models. The flow conditions are
compared against experimental data and the current state-of-the-art performance for
coefficient of pressure and coefficient of friction.
The simulation was performed as a two dimensional problem by restricting flow in the out-of-plane
direction through the use of a mesh that is one element thick. The upper and lower
walls are specified as no-slip, the inlet velocity and eddy viscosity are specified
normal to the inlet face to match the experimental Reynolds Number.
AcuSolve Results
The AcuSolve solution converged to a steady state and the results
reflect the mean flow conditions within the channel. As the fluid enters the channel
it develops into fully turbulent flow exhibiting a steep parabolic velocity profile
across the width of the channel. The flow begins to accelerate near the lower wall
and decelerate near the top wall as it approaches the 30° bend. The results show
that the upper (concave) wall destabilizes the boundary layer, increasing the eddy
viscosity and forcing the flow velocity to decrease. The following figures show the
flow conditions within the channel.
Upstream of the curved section of the channel, the flow normal to the channel opening increases
as the distance from the lower wall increases until it reaches the centerline of the
channel and then begins decreasing until it reaches zero at the top wall. As the
flow approaches the curved section, it begins to accelerate, requiring that the flow
velocity near the upper wall decrease to conserve momentum. The relatively low angle
of curvature in the channel does not cause the accelerated fluid to recirculate. The
images below show the coefficient of pressure (Cp) and coefficient of skin friction
(Cf) along the lower wall of the channel. The images show black circles representing
the experimental measurements (Smiths 1979), solid red lines for the SA model, solid
blue lines for the SST model, solid green lines for the K-ω model and a solid cyan
line for the K-ε model, representing the AcuSolve
results. The coefficient of pressure within the channel is predicted nearly
identically compared to the experiment for each of the turbulence models. It appears
that the SST and K-ε models capture the low velocity region with the best accuracy,
demonstrating that the flow velocity decreases significantly, but does not
recirculate within the channel. This is shown in the friction coefficient plot,
where the coefficient of friction, and subsequently the wall shear stress, does not
decrease below zero.
Summary
In this application, a turbulent flow through a curved channel at a Reynolds number of 2,100,000 is simulated and compared against experimental data. The
AcuSolve results compare well with the experimental data for pressure coefficient and skin friction coefficient within the channel. The performance of the Spalart Allmaras turbulence model was found to be consistent with previously published results for flow through a convex-curved channel (NASA 2015) and the SST turbulence model appears to predict the shear stress on the lower wall most accurately.
AcuSolve demonstrates the ability to predict the complex boundary layers resulting from the curvature of the channel and accurately predicts the propagation of the flow further downstream.
Simulation Settings for Turbulent Flow past a Convex Curve in a Channel
AcuConsole database file: <your working
directory>\convex_curvature_turbulent\convex_curvature_turbulent.acs
Global
Problem Description
Analysis type - Steady State
Turbulence equation - Spalart Allmaras
Auto Solution Strategy
Max time steps - 100
Convergence tolerance - 0.0001
Relaxation factor - 0.4
Material Model
Fluid
Density - 1.225 kg/m3
Viscosity - 1.8603e-5 kg/m-sec
Model
Volumes
Fluid - elbow
Element Set
Material model - Fluid
Fluid - inlet
Element Set
Material model - Fluid
Fluid - outlet
Element Set
Material model - Fluid
Surfaces
-Y
Simple Boundary Condition
Type - Slip
+Y
Type - Slip
Inlet
Simple Boundary Condition
Type - Inflow
Inflow type - Velocity
Inflow velocity type - Normal
Normal velocity - 31.9 m/sec
Turbulence input type - Direct
Eddy viscosity - 1.3671e-7
m2/sec
Internal
Simple Boundary Condition - (disabled)
Lower Wall
Simple Boundary Condition
Type - Wall
Turbulence wall type - Low Reynolds Number
Outlet
Simple Boundary Condition
Type - Outflow
Upper Wall
Simple Boundary Condition
Type - Wall
Turbulence wall type - Low Reynolds Number
References
A. J. Smits, S. T. B. Young, and P. Bradshaw. "The Effect of Short Regions of
High Surface Curvature on Turbulent Boundary Layers". Journal of Fluid
Mechanics. 94(2):209-242. 1979
NASA Langley Research Center Turbulence Modeling Resource webpage.
http://turbmodels.larc.nasa.gov/smitscurve_val.html. Accessed May
2015.