# KR522: How to setup a rotating flow when the mass flow inlet boundary condition is used in ANSYS FLUENT?

 Below are the 2 steps needed to set-up a mass flow-inlet with a 30 degrees rotation (or swirl).FIRST STEP: Define the axial directionBefore setting the boundary condition, one has to ensure that the 'axial' direction as referred in the boundary condition is correctly setup. The axial direction of your system must be equal to the axial direction as defined by the solver.This direction can be found (and modified) under define -> boundary conditions -> regions corresponding to a fluid-zone.Look for the motion tab for the rotation-axis direction panel: X,Y and Z define the direction of the 'axial direction'.FLUENT Default:2D: X is the axial direction (i.e. X = 1, Y = 0)3D: Z is the axial direction (i.e. X = 0, Y = 0 and Z = 1)Once the axial direction is defined, we can go to the second step and define the boundary conditionSTEP 2: Define the rotation angleWe will assume that the radial flow direction is 0.If the angle of swirl is 30 degrees, we have an axial component Vx = V * cos(30) and a tangential component Vtheta = V * sin(30).Hence, the input should be the following:Coordinate system: cylindricalRadial Component of Flow Direction: 0Tangential Component of Flow Direction: sin(30) (enter 0.5)Axial Component of Flow Direction: cos(30) (enter 0.866)