Define Objects: BC's


Define Objects: Surfaces| Volumes| Components| Bodies| Forces

To mark a surface with a particular boundary condition, double click on the surface in the "BC" Panel (alternatively, right-click and select "Edit BC").

Viscous Wall

Type: Viscous
Subtype: None		 Viscous conditions enforce a no-slip condition at the solid surface; in other words, the velocity of the fluid at the wall is equal to the velocity of the surface at the wall. 
Example:
  
surface 1 [name=Fuselage]: viscous;

 
 

Translating Surface

Type: Viscous
Subtype: Moving		 This boundary condition applies a specified velocity to a given surface. It overrides all other boundary conditions if a conflict should arise. It can be used in situations where it is not possible to move one surface relative to another, but the effects of the same are desired. An example of this type of situation is a rotating wheel that is in contact with a (relatively) translating road surface. The translational velocity is nondimensionalized by U_ref.
Example:
  
surface 1 [name=Road_Surface]: 
     viscous moving
     velocity = (1.0 0.0 0.0);

 
 

Spinning Bodies Of Revolution

Type: Viscous
Subtype: Spinning		 To specify a spinning body of revolution (typically a shaft) within the domain, one must give the axis of rotation and rotation rate. Note that all coordinates given must be nondimensionalized by L_ref . The nondimensional rotation rate (omega) is W_nd = W*L_ref/U_ref.
Example:
  
surface 1 [name=Left_Shaft]: 
     viscous rotating
     p1 = (0.0 0.0 0.0)
     p2 = (0.0 0.0 1.0)
     omega = 2.0;

 
 

Laminar Wall

Type: Viscous
Subtype: Laminar		 A laminar condition enforces a no-slip condition at the solid surface; additionally, it attempts to simulate relaminarization on a surface during the solution of the turbulence model by excluding the points on this surface from the turbulence distance computation.
Example:
  
surface 1 [name=Fuselage]: viscous laminar;

 
 

Solid/Inviscid Wall

Type: Inviscid
Subtype: None		 A solid wall boundary condition enforces local flow tangency to the surface. Usually, this boundary condition is not valid for viscous flows; viscous (no-slip) conditions should be used instead.
Example:
  
surface 1 [name=Solid_Wall]: inviscid;
or equivalently 
surface 1 [name=Solid_Wall]: solid;

 
 

Farfield Boundary

Type: Farfield
Subtype: None		 The farfield boundary condition is a characteristic variable based condition which allows flow to enter or leave the domain, as appropriate.

Typically, the velocity at the farfield will always be unity (since U_ref = U_inf). However, the "uinf" parameter allows for a situation in which this is not the case.

Example:
  
surface 1 [name=Outer_Boundary]: farfield
     uinf = 1.0;

 
 

Farfield Boundary, Specified Back Pressure

Type: Farfield
Subtype: Backpressure		 [This boundary condition is currently unsupported under uss_u2ncle, but can be specified in the solver .bc file]. The farfield boundary condition is a characteristic variable based condition which allows flow to leave the domain when the downstream pressure is known. Also, the approximate direction vector of the downstream flow must be given to form a reference state for the characteristic variable formulation.
Example:
  
surface 1 [name=My_Outlet]: outlet backpressure = 0.8 direction = (1.0 0.0 0.0);

 
 

Symmetry Plane

Type: Symmetry
Subtype: Mirrored		 This boundary condition enforces no flux through the symmetry surfaces, as well as zero normal derivatives of all variables at the symmetry plane. It enforces the symmetry condition by mirroring elements that touch a symmetry plane. The point and normal specified in the definition of the boundary condition are used to define the plane of symmetry. Note that the coordinates given should be nondimensionalized by L_ref.

The normal vector defining the symmetry plane must be oriented such that it points out of the computational domain. Also, this boundary condition is appropriate only for planar surfaces.

Example:
  
surface 1 [name=Symmetry_Plane]: mirror 
      point = (0.0 0.0 0.0) 
      normal = (0.0 0.0 -1.0);

 
 

Symmetry Surface

Type: Symmetry
Subtype: Direct		 This variant of the symmetry boundary condition can be used when the "symmetry" surface is not necessarily planar, but one still wishes to impose zero normal derivatives of all variables.
Example:
  
surface 1 [name=Symmetry_Surface]: symmetry;

 
 

Free Surface

Type: Freesurface
Subtype: None		 A free surface boundary condition is used when a surface defines an interface between two immiscible fluids, for example, an air-water interface. The free surface is free to move and deform with the deformation being driven by the flow past either a fully submerged (submarine) or partially submerged (ship) obstacle. This option is used in conjunction with the -freesurf option of the flow solver.
Example:
  
surface 1 [name=Water]: freesurface;

 
 

Outflow Surface

Type: Outflow
Subtype: None		 This is a simple extrapolation boundary condition. The values from the inside of the domain are imposed on the boundary during the flux and Jacobian evaluations.
Example:
  
surface 1 [name=Outflow]: 
     outflow pexit = 0.0;

 
 

Body Force Propulsor

Type: Bodyforce
Subtype: None		 This boundary condition is used to simulate the effects of a propulsor using a simple body force model. Nondimensional thrust [T/(rho_ref*U_ref^2*L_ref^2)] and torque [Q/(rho_ref*U_ref^2*L_ref^3)], in addition to propulsor location and propulsor orientation (normal to the propulsor plane) are required as input. Also required are the propeller radius and hub radius. In addition, the loading distribution type is also required. Valid load distributions are:
  0  uniform distribution for thrust and torque force (linear load distribution for torque)
  1  sinusoidal circulation distribution for thrust and torqe force
  2  sinusoidal circulation distribution for thrust and torque
The torque force is the resultant force obtained by dividing the torque by the moment arm.
Example:
  
surface 1 [name=Actuator_Disk]: 
     interior bodyforce
     thrust = 0.5
     torque = 0.1
     hub_radius = 2.0
     prop_radius = 5.0
     prop_loc = (0.94 0.0 0.0)
     prop_dir = (1.0 0.0 0.0)
     load_dis = 2;

 
 

Injector

Type: Injector
Subtype: None		 This boundary condition is used to simulate the effects of an injector on the given surface.  Non-dimensional mass, momentum, and energy are required as input.  The non-dimensional mass, momentum, and energy are the normalized total massflow, momentum, and energy being added by all injectors.  The local-dir specified in the definition of the boundary condition is a vector which defines the direction of the momentum force in the local cylindrical coordinates (x, r, t), and rotor-dir is the rotational direction for the grid in either absolute or rotating frame (x, y, z).
Example:
  
surface 1 [name=Injector]: 
     interior injector
     mass = 0.5
     momentum = 0.1
     energy = 2.0
     local_loc = (1.0 0.0 0.0)
     rotor_dir = (1.0 0.0 0.0);

 
 

Transparent Surface

Type: Transparent
Subtype: None		 This is a generic surface which has no physical boundary condition associated with it. It arises when multiple grids are merged together using gridmerge. The purpose of this surface is to provide better control over the clustering of points. Consequently, they are placed in regions of interest.

The solver completely ignores interior surfaces.

Example:
  
surface 1 [name=Trans_Surface]: interior;

 
 

Transparent Sliding

Type: Transparent
Subtype: Sliding UVI		 A transparent sliding (UVI) surface is a special case of a transparent surface. It must be a surface of revolution and is used to provide a mechanism for handling geometric entities which rotate about specified axes, for example, propulsors.
Example:
  
surface 1 [name=UVI]: interior sliding;

 
 

Transparent Sliding Primary

Type: Transparent
Subtype: Sliding Primary		 A transparent sliding primary surface is a special case of a transparent surface. It must be paired with a corresponding transparent sliding secondary surface. A sliding primary/secondary surface is used to couple disjoint grids together. The primary surface and corresponding secondary surfaces should represent the same area, however they do not have to have the same discretization. For use within a rotating volume, it must be a surface of revolution and is used to provide a mechanism for handling geometric entities which rotate about specified axes, for example, propulsors. For non-rotating volumes where it is used to to couple grids together, the surface does not have to be a surface of revolution.
Example:
  
surface 1 [name=Primary_Interface]: interior primary
          partner = 2;

 
 

Transparent Sliding Secondary

Type: Transparent
Subtype: Sliding Secondary		 A transparent sliding secondary surface is a special case of a transparent surface. It must be paired with a corresponding transparent sliding primary surface. A sliding primary/secondary surface is used to couple disjoint grids together. The primary surface and corresponding secondary surfaces should represent the same area, however they do not have to have the same discretization. For use within a rotating volume, it must be a surface of revolution and is used to provide a mechanism for handling geometric entities which rotate about specified axes, for example, propulsors. For non-rotating volumes where it is used to to couple grids together, the surface does not have to be a surface of revolution.
Example:
  
surface 2 [name=Secondary_Interface]: interior secondary
          partner = 1;

 
 

Protected Surface

Type: Transparent
Subtype: Protected		 Marking a surface as protected ensures that the domain decomposition process does not destroy its integrity by partitioning through it. A protected surface, by definition, is a closed surface. It has no physical boundary condition associated with it. Its purpose is to provide an interface within which relative motion can take place, for example, between a stern appendage and a hull.
Example:
  
surface 1 [name=Protected_Surface]: 
     interior protected;

 
 

Protected Shared Surface

Type: Transparent
Subtype: Protected Shared		 This is a special case of the protected surface boundary condition. Marking a surface with this boundary condition makes it available to multiple protected surfaces so that each one can form a closed surface.
Example:
  
surface 1 [name=Protected_Shared]: 
     interior protected shared;

 
 

Nearfield Inflow

Type: Nearfield Inflow
Subtype: None		 The nearfield inflow condition is exactly the same as the farfield condition, except that the pressure outside the boundary is set to the pressure inside the boundary (as opposed to P_inf). This allows the pressure to float freely at the expense of wave reflections (leading to slower convergence) that might occur due to a noncharacteristic variable boundary condition at the outer boundary of the domain.
Example:
  
surface 1 [name=Inflow]: farfield inflow
     uinf = 1.0;

 
 
 
 

For further information related to the materials in this web site, USS_U2NCLE, U2NCLE,  SolidMesh, DIVA or information related to their use, please contact:

David L. Marcum
marcum@erc.msstate.edu

Phone: (662) 325-3193,   FAX: (662) 325-7692

Computational Simulation and Design Center
Engineering Research Center for Computational Field Simulation
Mississippi State University
Box 9627, Mississippi State, MS  39762

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