flec04

Objectives

• Understand the types of available boundary conditions and their applications.

Lecture

• Boundary conditions

Labs

• Complicated geometries (guided)
• Boundary condition comparison
• External flow (Ahmed car body)
• Internal flow (tube bank)

Order of Class

• Comp. geom. lab 10m 14h00
• BC lecture 15m 14h10
• Internal lab 25m 14h25
• External lab 25m 14h50

Boundary Conditions

Why defining boundary conditions?

Information must be provided on the boundaries so that the governing PDEs have a unique solution.

Defining boundary conditions involves identifying the location of the boundaries and supplying information at the boundaries.

Fluent offers a number of choices of boundary types to accommodate various availability of information.

• Velocity Inlet
  • Specifies a uniform velocity profile at the boundary
  • Other properties can also be defined such as temperature
  • Only for incompressible flow
  • Supersonic/Initial Gauge Pressure defines the static pressure where flow is supersonic or is ignored if subsonic. It will also be used to initialize solution
• Pressure Inlet
  • Specifies the gauge total pressure
  • Suitable for compressible and incompressible flows
  • Velocity and static pressure are calculated (Bernoulli's equation for incompressible flow and isentropic relations for compressible flow)
  • Supersonic/Initial Gauge Pressure same as in velocity inlet
• Mass Flow Inlet
  • Specifies a uniform mass flow rate at the boundary
  • Generally intended for compressible flows but can be used on incompressible flows as well
• Pressure Outlet
  • Specifies the static pressure of the environment into which flow exhausts
• Outflow
  • No pressure or velocity information is required
  • Solution at the boundary is extrapolated from interior assuming zero normal flux
  • Need Flow Rate Weighting in case of multiple outflow boundaries
• Pressure Far-field
  • Models a free-stream compressible flow at infinity
  • Specifies static pressure and Mach number
• Symmetric and Axisymmetric Boundary
• Periodic Boundary
  • Rotational periodicity
    • dP = 0 across periodic planes
  • Translational periodicity
    • Models fully developed flow conditions
    • Specifies either dP or mass flow rate per period