Boundary Conditions

Boundary Conditions#

Boundary conditions define the physical behavior at each surface of your mesh. Correct boundary conditions are critical for obtaining meaningful simulation results.

Automatic Detection#

Studio automatically assigns boundary conditions based on surface names:

Surface Name Contains	Assigned Type	Default Values
`inlet`	Velocity inlet	Must specify velocity
`outlet`	Pressure outlet	0 Pa gauge
`wall`, `body`, `car`, `wing`	No-slip wall	Zero velocity at surface
`symmetry`	Symmetry	—
`ground`	Moving wall	Velocity matches freestream
`top`, `side`, `farfield`	Slip wall	—

You can override any auto-detected condition in the Simulation tab.

Inlet Conditions#

Velocity Inlet#

The most common inlet type. Specify the flow velocity entering the domain.

Parameter	Description	Example
Velocity	Flow speed magnitude and direction	30 m/s in X-direction
Turbulence intensity	Incoming turbulence level as a percentage	1–5% for external, 5–10% for internal
Turbulent viscosity ratio	Ratio of turbulent to molecular viscosity	5–100

Turbulence Intensity Guide

Application	Typical TI
Wind tunnel (low turbulence)	0.5 – 1%
External flow (atmospheric)	1 – 5%
Internal flow (duct, pipe)	5 – 10%
Highly turbulent environments	10 – 20%

The turbulence quantities (k, ω, ε) are automatically computed from the turbulence intensity and viscosity ratio — you don’t need to calculate these manually.

Outlet Conditions#

Pressure Outlet#

Sets a fixed static pressure at the boundary. This is the standard outlet condition for most incompressible flow problems.

Parameter	Description	Typical Value
Static pressure	Gauge pressure at the outlet	0 Pa

Note

For incompressible flow (the default in Gradient Dynamics), absolute pressure doesn’t matter — only pressure differences. Setting the outlet to 0 Pa gauge is standard practice.

Wall Conditions#

No-Slip Wall#

The default wall condition. Fluid velocity is zero at the surface (the fluid “sticks” to the wall).

Use for: Solid surfaces — car bodies, pipe walls, wing surfaces, buildings

Moving Wall#

A wall with a prescribed velocity. The fluid matches this velocity at the surface.

Parameter	Description	Example
Wall velocity	Velocity vector of the wall surface	Ground moving at freestream speed

Use for:

Ground plane in vehicle aerodynamics — the ground moves at the same speed as the incoming airflow to simulate a car moving through still air
Rotating walls — wheels, rotating cylinders

Slip Wall#

Zero shear stress at the surface — the fluid slides freely along the wall.

Use for: Far-field boundaries (top, sides of external domain), symmetry-like conditions where you don’t want to enforce exact symmetry

Symmetry#

Mirrors the flow field across the boundary. No flow crosses the symmetry plane, and all gradients normal to the plane are zero.

Use for: Symmetric geometries where you mesh only half (or quarter) of the domain to reduce cell count and compute cost.

Symmetry Assumptions

Only use symmetry if your flow is truly symmetric. Bluff body flows, for example, may have asymmetric vortex shedding that a symmetry condition would suppress. For RANS, symmetry is generally safe for geometrically symmetric configurations.