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May 24, 2011, 03:24 
flow analysis

#1 
Senior Member
Govindaraju
Join Date: Apr 2010
Posts: 207
Rep Power: 10 
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(1r^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: 615
Rep Power: 15 
First of all, do you need the pressure to vary between 80120 mmHg? If so, why do you do a steadystate 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 (gammatheta) 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: 207
Rep Power: 10 
Quote:
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]*tpi/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]*tpi/2)) vin2 = 0.3[m s^1]*(1r^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.E4 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 = kway 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: 615
Rep Power: 15 
See for example: http://www.cfdonline.com/Wiki/Ansys...gence_criteria


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