/BEM/FLOW

Block Format Keyword Describes the incompressible fluid flow by boundary elements method.

Format

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
/BEM/FLOW/flow_ID/unit_ID
flow_title
surf_IDex Nio Iinside Ifsp Fscalesp Ascalesp    
grn_IDaux Itest Tole            
Rho Ivinf              
surf_IDio fct_IDvel fct_IDpr   Fscalenv Fscalepres Ascalet
Iform Ipri Dtflow            
Ifvinf Fscalevel Ascalevel          
Dirx Diry Dirz        

Definitions

Field Contents SI Unit Example
flow_ID Incompressible flow block identifier.

(Integer, maximum 10 digits)

  
unit_ID Unit Identifier.

(Integer, maximum 10 digits)

  
flow_title Incompressible flow block title.

(Character, maximum 100 characters)

  
surf_IDex Flow external surface identifier.

(Integer)

  
Nio Number of inflow-outflow surfaces.

(Integer)

  
Iinside Inside or outside flow flag.
= 1 (Default)
Flow is computed inside the surface defined by surf_IDex. The surface element normals must be oriented outwards.
= 2
Flow is computed outside the surface defined by surf_IDex. The surface element normals must be oriented inwards.

(Integer)

  
Ifsp Stagnation pressure curve number.

(Integer)

  
Fscalesp Stagnation pressure scale factor.

Default = 1.0 (Real)

 [ Pa ]
Ascalespc Abcissa scale factor for stagnation pressure curve.

Default = 1.0 (Real)

 [ s ]
grn_IDaux Auxiliary nodes group identifier. 2

(Integer)

  
Itest Test auxiliary nodes flag. 2

(Integer > 0)

  
Tole A dimensional tolerance. 2

Default = 1.e-5 (Real)

  
Rho Fluid density.

(Real)

 [ kg m 3 ]
Ivinf Additional velocity field flag. 3

(Integer > 0)

  
surf_IDio Inflow-Outflow surface identifier. 4

(Integer)

  
fct_IDnv Normal velocity curve. 4

(Integer)

  
fct_IDpres Imposed pressure curve. 5

(Integer)

  
Fscalenv Normal velocity scale factor.

Default = 1.0 (Real)

 [ m s ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaamWaaeaada Wcaaqaaiaab2gaaeaacaqGZbaaaaGaay5waiaaw2faaaaa@39DE@
Fscalepres Imposed pressure scale factor.

Default = 1.0 (Real)

 [ Pa ]
Ascalet Abscissa scale factor for normal velocity curve and imposed pressure curve.

Default = 1.0 (Real)

 [ s ]
Iform Formulation flag. 6
= 1
Fluid flow is computed using BEM with a collocation approach to solve the integral equation.
= 2
Fluid flow is computed using BEM with a galerkin approach to solve the integral equation.

(Integer > 1)

  
Ipri Output level.

(Integer > 1)

  
Dtflow Time step for BEM matrices assembly. 7

Default = 0 (Real)

 [ s ]
Ifvinf Velocity curve.

(Integer)

  
Fscalevel Velocity scale factor.

Default = 1.0 (Real)

 [ m s ] MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaamWaaeaada Wcaaqaaiaab2gaaeaacaqGZbaaaaGaay5waiaaw2faaaaa@39DE@
Ascalevel Abscissa scale factor for velocity curve.

Default = 1.0 (Real)

 [ s ]
Dirx X component of the additional field direction vector.

(Real)

  
Diry Y component of the additional field direction vector.

(Real)

  
Dirz Z component of the additional field direction vector.

(Real)

  

Comments

  1. The surf_IDex must define a closed surface.
  2. Using BEM, the flow potential, velocity and pressure are computed for nodes belonging to the surface defined by surf_IDex.

    For visual and post-treatment concerns, the flow characteristics can be computed for a set of nodes inside the flow belonging to grn_IDaux.

    If Itest = 1, whether the auxiliary nodes are actually located inside (if Iinside =1) or outside (if Iinside =2), the surface defined by surf_IDex at each time step is tested. Wrong nodes are then canceled for the current time step.

    Tolerance Tole is used to perform the point-inside-closed-surface test.

  3. Flag Ivinf is only effective for flow computation in an unbounded domain outside the surface defined by surf_IDex (Iinside =2).

    If Ivinf = 1, an inflow condition is defined by an additional homogeneous flow defined in free space. The computed flow will be identical to the additional flow at an infinite distance from the surface defined by surf_IDex.

  4. If Iinside = 0: there must be at least one surface where the normal velocity is imposed and one, and only one surface where the normal velocity is left free. The velocity at the free surface will be computed thanks to flux equilibrium on the global surface defined by surf_IDex.

    If Iinside = 2 and Ivinf = 0: same as above.

    If Iinside = 2 and Ivinf = 1: the number of surfaces is free and the normal velocity must be imposed on all of them.

  5. In order to reduce pressure from the velocity field, one and only one pressure must be imposed for the entire flow computation: it can be whether the global stagnation pressure or the pressure at one of the inflow-outflow surfaces.
  6. The collocation approach is faster but may not be robust enough to handle very complex geometries.

    The galerkin approach works in every situation but is significantly slower.

  7. BEM matrices depend only on the geometry of the surface.

    If Dtflow = 0 (default), they are assembled at every cycle of the simulation (the time step being classically given by the stability condition of finite elements).

    If Dtflow ≠ 0:,max(Dtflow, Dt) is used to update to BEM matrices; where Dt is the finite element time step.