[Note: It might be the case that this information has already been shared on the CFX forum but this is an effort to bring it under one thread.]
Quantifying swirl becomes very important in some situations where you would like to reduce it or even sometimes when requirement of design is to increase the swirl.
Swirl Number:
The degree of swirl in the flow can be quantified by the dimensionless parameter, Sn, known as the swirl number which is defined as the ratio of the axial flux of angular momentum to the axial flux of axial momentum:
http://www.cfd-online.com/Forums/att...1&d=1331804552
To calculate in the CFX, create the following CEL expression;
Swirl Number [non dimensional] = areaInt(Density*sqrt(Velocity v*Velocity v)*sqrt((Velocity u*Velocity u)+(Velocity w*Velocity w))*sqrt((X*X)+(Z*Z)))@Plane 1/(maxVal(sqrt((X*X)+(Z*Z)))@Plane 1*areaInt(Density*Velocity v*Velocity v)@Plane 1)
Where
areaInt = Area Integral
sqrt = Square Root
Velocity v = Velocity in mean flow direction i.e. Y-axis in this case
Velocity u = Velocity in X-axis
Velocity w = Velocity in Z-axis
maxVal = Maximum Value
Y-axis is perpendicular to Plane 1, while X-axis and Z-axis are parallel to the Plane1 in this case.
For centrifugal pump impeller design it should be between 0.05-0.1 for good suction performance or 0.01 for excellent suction performance.
Swirl Angle:
This is again very important for specifying the blade angles in centrifugal pumps.
Use following CEL expression;
Swirl Angle[radians] = atan2(sqrt(Velocity u^2+Velocity w^2), sqrt(Velocity v^2))
Where
atan2 = arctangent
sqrt = Square Root
Velocity v = Velocity in mean flow direction i.e. Y-axis in this case
Velocity u = Velocity in X-axis
Velocity w = Velocity in Z-axis
Y-axis is perpendicular to Plane 1, while X-axis and Z-axis are parallel to the Plane1 in this case
Then create a variable SwirlAngleVariable to calculate an area average over the plane, this would give you a value in degrees.
