Quantifying the swirl in CFX, Swirl Number/Swirl Angle

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 May 1, 2012, 01:06 #21 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,560 Rep Power: 97 Have a look in my PhD thesis - http://hdl.handle.net/2100/248 See page 74, in the literature review.

May 2, 2012, 22:35
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 Originally Posted by ghorrocks Have a look in my PhD thesis - http://hdl.handle.net/2100/248 See page 74, in the literature review.
Thanks. The formula is for combustion within the cylinder of an IC engine, and includes "omega" - the crankshaft velocity. Would this relate to a gas turbine engine combustor, where there is no rotating component? The swirl could be introduced in the gas by means of swirl vanes around the inlet nozzle of the gas?

 May 2, 2012, 23:48 #23 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 12,560 Rep Power: 97 I mentioned this because I wanted to make the point that there is no universal definition of swirl number. It is defined based on what makes sense in the application. In IC engines it makes a lot of sense to normalise against crankshaft velocity as it is the scaling factor on all engine flows. But for a GT this may not be the case, so an equivalent swirl number normalised by shaft speed may be meaningless.

July 24, 2016, 22:28
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 Originally Posted by tauqirnawaz [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: 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.
Hello tauqirnawaz
I confused for CEL equation.
The W in the swirl number equation is tangential velocity. So, why you use sqrt((Velocity u^2)+(Velocity w^2)) for the W ?
Why isn't velocity u or velocity w used for W?

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