# flow analysis

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 May 24, 2011, 03:24 flow analysis #1 Senior Member   Govindaraju Join Date: Apr 2010 Posts: 206 Rep Power: 8 Dear friend I am doing Blood flow analysis in a stenosed artery. (Steady state simulation) I created venturi type solid model (Blood domain ) The flow is Z direction I assume flow rate is 50 ml/min from which I calculated the velocity (Q= Av : Continuity equation) I set the inlet velocity as Umax(1-r^2/R^2) outlet : Mass and momentum >Average Static pressure= 0 Pa Is this correct? I set Domain models>reference pressure 1 atm But I have seen in many papers the pressure varies between 80mm Hg - 120mm Hg.( Diastole -Systole Pressure) But I did n't use the above pressure anywhere. In CFX post , Which pressure measurement is suitable ? Is it Total pressure or pressure? when I did the simulation I checked the Total pressure before the stenosis the pressure is Approx 230Pa . In a venturi region pressure drops but after venturi the flow pressure decreases and decreases Why not the pressure is recovered to 230 Pa ?Where can I implement 80mm Hg pressure or 120mm Hg pressure in the simulation. Please help me to set up the boundary condition. If I want to introduce transition analysis How can I introduce it. Please help me to give tips Thank you Regards Govind

 May 24, 2011, 05:27 #2 Senior Member   Lance Join Date: Mar 2009 Posts: 522 Rep Power: 11 First of all, do you need the pressure to vary between 80-120 mmHg? If so, why do you do a steady-state simulation? To prescribe a varying pressure at the outlet have a look at http://www.edr.no/blogg/ansys_blogge...nsient_profile Velocity profile at inlet and pressure at outlet seems like reasonable BCs. Regarding transition, consider RANS models (gamma-theta) or LES. Have a look in a CFD text book for the details. Also, you really should consider a basic course in CFD.

May 26, 2011, 05:00
Transient analysis
#3
Senior Member

Govindaraju
Join Date: Apr 2010
Posts: 206
Rep Power: 8
Quote:
 Originally Posted by Lance First of all, do you need the pressure to vary between 80-120 mmHg? If so, why do you do a steady-state simulation? To prescribe a varying pressure at the outlet have a look at http://www.edr.no/blogg/ansys_blogge...nsient_profile Velocity profile at inlet and pressure at outlet seems like reasonable BCs. Regarding transition, consider RANS models (gamma-theta) or LES. Have a look in a CFD text book for the details. Also, you really should consider a basic course in CFD.
Dear Mr Lance

I tried Transient analysis . But I have convergent problem.
I increased the length of the artery too. The flow is Z dirction

My inlet velocity is
U=0
V=0
W= 0.2[m/s]*(1+sin(2*pi*2[Hz]*t-pi/2)

I set the pressure at the outlet 0 Pa

initial condition ; U=0, V=0, W= 0 and pressure =0

Here is the

CFX Command Language for Run for your reference. Kindly help me . Because I need a pressure at every point . |
| |
+--------------------------------------------------------------------+

LIBRARY:
CEL:
EXPRESSIONS:
vin = 0.1[m s^-1]*(1+sin(2*pi*2[Hz]*t-pi/2))
vin2 = 0.3[m s^-1]*(1-r^2/(0.0014[m])^2)
END
END
MATERIAL: Blood
Material Group = User
Option = Pure Substance
Thermodynamic State = Liquid
PROPERTIES:
Option = General Material
EQUATION OF STATE:
Density = 1060 [kg m^-3]
Molar Mass = 1.0 [kg kmol^-1]
Option = Value
END
DYNAMIC VISCOSITY:
Option = Non Newtonian Model
NON NEWTONIAN VISCOSITY MODEL:
High Shear Viscosity = 0.00345 [Pa s]
Low Shear Viscosity = 0.056 [Pa s]
Option = Bird Carreau
Power Law Index = 0.3568
Time Constant = 3.313 [s]
END
END
END
END
END
FLOW: Flow Analysis 1
SOLUTION UNITS:
Angle Units = [rad]
Length Units = [m]
Mass Units = [kg]
Solid Angle Units = [sr]
Temperature Units = [K]
Time Units = [s]
END
ANALYSIS TYPE:
Option = Transient
EXTERNAL SOLVER COUPLING:
Option = None
END
INITIAL TIME:
Option = Value
Time = 0 [s]
END
TIME DURATION:
Option = Total Time
Total Time = 2 [s]
END
TIME STEPS:
Option = Timesteps
Timesteps = 0.1 [s]
END
END
DOMAIN: Default Domain
Coord Frame = Coord 0
Domain Type = Fluid
Location = B27
BOUNDARY: inlet
Boundary Type = INLET
Location = in
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Option = Cartesian Velocity Components
U = 0 [m s^-1]
V = 0 [m s^-1]
W = vin
END
END
END
BOUNDARY: out
Boundary Type = OUTLET
Location = out
BOUNDARY CONDITIONS:
FLOW REGIME:
Option = Subsonic
END
MASS AND MOMENTUM:
Option = Average Static Pressure
Pressure Profile Blend = 0.05
Relative Pressure = 0 [Pa]
END
PRESSURE AVERAGING:
Option = Average Over Whole Outlet
END
END
END
BOUNDARY: wall
Boundary Type = WALL
Location = wall
BOUNDARY CONDITIONS:
MASS AND MOMENTUM:
Option = No Slip Wall
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Option = Non Buoyant
END
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Option = None
END
REFERENCE PRESSURE:
Reference Pressure = 1 [atm]
END
END
FLUID DEFINITION: Fluid 1
Material = Blood
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Option = None
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = Laminar
END
END
END
INITIALISATION:
Option = Automatic
INITIAL CONDITIONS:
Velocity Type = Cartesian
CARTESIAN VELOCITY COMPONENTS:
Option = Automatic with Value
U = 0 [m s^-1]
V = 0 [m s^-1]
W = 0 [m s^-1]
END
STATIC PRESSURE:
Option = Automatic with Value
Relative Pressure = 0 [Pa]
END
END
END
OUTPUT CONTROL:
RESULTS:
File Compression Level = Default
Option = Standard
END
TRANSIENT RESULTS: Transient Results 1
File Compression Level = Default
Include Mesh = No
Option = Selected Variables
Output Variables List = Pressure,Velocity
OUTPUT FREQUENCY:
Option = Every Timestep
END
END
END
SOLVER CONTROL:
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 10
Minimum Number of Coefficient Loops = 1
Timescale Control = Coefficient Loops
END
CONVERGENCE CRITERIA:
Residual Target = 1.E-4
Residual Type = RMS
END
TRANSIENT SCHEME:
Option = Second Order Backward Euler
TIMESTEP INITIALISATION:
Option = Automatic
END
END
END
END
COMMAND FILE:
Version = 13.0
Results Version = 13.0
END
SIMULATION CONTROL:
EXECUTION CONTROL:
EXECUTABLE SELECTION:
Double Precision = Off
END
INTERPOLATOR STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
END
PARALLEL HOST LIBRARY:
HOST DEFINITION: govindaraju
Host Architecture String = winnt
Installation Root = C:\Program Files\ANSYS Inc\v%v\CFX
END
END
PARTITIONER STEP CONTROL:
Multidomain Option = Independent Partitioning
Runtime Priority = Standard
EXECUTABLE SELECTION:
Use Large Problem Partitioner = Off
END
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARTITIONING TYPE:
MeTiS Type = k-way
Option = MeTiS
Partition Size Rule = Automatic
END
END
RUN DEFINITION:
Run Mode = Full
Solver Input File = Model1.def
END
SOLVER STEP CONTROL:
Runtime Priority = Standard
MEMORY CONTROL:
Memory Allocation Factor = 1.0
END
PARALLEL ENVIRONMENT:
Number of Processes = 1
Start Method = Serial
END
END
END
END

May 26, 2011, 05:09
#4
Senior Member

Lance
Join Date: Mar 2009
Posts: 522
Rep Power: 11
Quote:
 Originally Posted by kmgraju I tried Transient analysis . But I have convergent problem.
See for example: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

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