CFD boundary Conditions

For your CFD simulation CONSELF provides a very high number of different settings. In general the boundary available are grouped in few types:

  • INLET -> flow inlet into the system
  • OUTLET -> flow outlet
  • IN/OUT -> boundaries that can define both an inlet or outlet (surface normal vectors are positive if inlet, negative when outlet)
  • WALL -> solid walls of the system

Starting from this raw classification, each boundary is specialized and gives a number of feature to the user to reproduce reality as accurately as possible. Remember that some of these boundary conditions are available according to the application you are using and also to the fluid model chosen.

Once you select the appropriate boundary for your models, a certain number of inputs are required, such as pressure values, velocities, temperatures, etc. Using this page you can have a complete list of all these options with hints to choose correct values.

WALL boundaries highly affect the quality of your simulation, in combination with wall refinement and the turbulence model. Guidelines about an appropriate selection are given in this blog post.

Boundary Description
IN/OUT - Total pressure
Total pressure inlet and outlet condition
  • p [Pa] - Total pressure
  • Φ [%] - Fluid-A volume concentration
IN/OUT - Velocity
Inlet and outlet velocity - Velocity vector normal to the surface (use negative value for outflow)
  • U [m/s] - Velocity
  • Dₕ [m] - Hydraulic diameter
  • s [unit/m³] - Passive scalar value
IN/OUT - Velocity fixed temperature
Inlet and outlet velocity with specified temperature - Velocity vector normal to the surface
  • U [m/s] - Velocity
  • T [K] - Temperature
  • Dₕ [m] - Hydraulic diameter
IN/OUT - Velocity vector
Inlet and outlet velocity where the user specifies the velocity vector
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • Dₕ [m] - Hydraulic diameter
  • s [unit/m³] - Passive scalar value
IN/OUT - Velocity vector fixed temperature
Inlet and outlet velocity where the user specifies the velocity vector and the temperature
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • T [K] - Temperature
  • Dₕ [m] - Hydraulic diameter
IN/OUT - Volume flow
Inlet and outlet condition with prescribed volume flow (use negative value for outflow)
  • Q [m³/s] - Volume flow
  • Dₕ [m] - Hydraulic diameter
  • s [unit/m³] - Passive scalar value
IN/OUT - Volume flow fixed temperature
Inlet and outlet condition with prescribed volume flow and temperature (use negative value for outflow)
  • Q [m³/s] - Volume flow
  • T [K] - Temperature
  • Dₕ [m] - Hydraulic diameter
INLET - Absolute velocity
Inlet velocity - Velocity vector is specified in an absolute reference frame
  • Uabsx [m/s] - Absolute velocity X
  • Uabsy [m/s] - Absolute velocity Y
  • Uabsz [m/s] - Absolute velocity Z
  • Dₕ [m] - Hydraulic diameter
INLET - Cylindrical velocity
Inlet velocity in a cylindrical reference frame
  • Centre X [m] - Centre X
  • Centre Y [m] - Centre Y
  • Centre Z [m] - Centre Z
  • Axis X - Normalized axis X
  • Axis Y - Normalized axis Y
  • Axis Z - Normalized axis Z
  • U axial [m/s] - Axial velocity
  • U radial [m/s] - Radial velocity
  • ω [rpm] - Rotational velocity
  • Dₕ [m] - Hydraulic diameter
INLET - Relative velocity
Inlet velocity - Velocity vector is specified in a relative reference frame
  • Urelx [m/s] - Relative velocity X
  • Urely [m/s] - Relative velocity Y
  • Urelz [m/s] - Relative velocity Z
  • Dₕ [m] - Hydraulic diameter
INLET - Total pressure
Total pressure inlet condition
  • pₜ [Pa] - Total Pressure
  • Dₕ [m] - Hydraulic diameter
  • s [unit/m³] - Passive scalar value
INLET - Velocity
Inlet velocity - Velocity vector normal to the surface
  • U [m/s] - Velocity
  • Φ [%] - Fluid-A volume concentration
  • Dₕ [m] - Hydraulic diameter
INLET - Velocity and particles
Inlet velocity with specified inlet particles
  • U [m/s] - Fluid velocity
  • Uxₚ [m/s] - Particles velocity X
  • Uyₚ [m/s] - Particles velocity Y
  • Uzₚ [m/s] - Particles velocity Z
  • Mₚ [kg] - Particles total mass
  • Dₚ [m] - Particles dimension
  • Dₕ [m] - Hydraulic diameter
INLET - Velocity vector
Inlet velocity where the user specifies the velocity vector
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • Φ [%] - Fluid-A volume concentration
  • Dₕ [m] - Hydraulic diameter
OUTLET - Pressure
Outlet condition for pressure - Backscatter flow is denied
  • p [Pa] - Absolute pressure
OUTLET - Velocity
Outlet velocity - Velocity vector normal to the surface
  • U [m/s] - Velocity
WALL - Adiabatic no slip
No slip adiabatic wall
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
WALL - Fire location
No slip wall with imposed temperature gradient
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • s [unit/(s·m²)] - Passive scalar production
  • q [W/m²] - Heat flux
WALL - No slip
No slip adiabatic wall
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
WALL - No slip fixed temperature
No slip wall with imposed temperature
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • T [K] - Temperature
  • s [unit/(s·m²)] - Passive scalar production
WALL - No slip rough wall
No slip rough wall
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • Ks [m] - Sand-grain roughness height
  • Cs - Roughness constant
WALL - No slip with heat flux
No slip wall with imposed heat flux per surface unit
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • q [W/m²] - Heat flux
  • s [unit/(s·m²)] - Passive scalar production
  • ∇T [K/m] - Temperature gradient
WALL - No slip with heat power
No slip wall with imposed global heat flux
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • Q [W] - Heat power
WALL - No slip with passive scalar production
No slip wall with imposed CO production
  • Ux [m/s] - Velocity X
  • Uy [m/s] - Velocity Y
  • Uz [m/s] - Velocity Z
  • s [unit/(s·m²)] - Passive scalar production
WALL - Rotating
Rotating adiabatic wall
  • Centre X [m] - Centre X
  • Centre Y [m] - Centre Y
  • Centre Z [m] - Centre Z
  • Axis X - Normalized axis X
  • Axis Y - Normalized axis Y
  • Axis Z - Normalized axis Z
  • ω [rpm] - Rotational velocity
WALL - Rotating no slip
Rotating adiabatic wall
  • ω [rpm] - Relative rotational speed
WALL - Rotating no slip rough wall
No slip rotating rough wall
  • ω [rpm] - Relative rotational speed
  • Ks [m] - Sand-grain roughness height
  • Cs - Roughness constant