Dynamic pressure from the total pressure specified

saisanthoshm88 · August 9, 2012, 06:18

Could some one please let me know how does CFX compute / separate the static pressure and dynamic pressure when a total pressure is specified at an inlet.

Because I suppose that in a problem where a total pressure is specified at the inlets and static pressure at outlets, the solver should some how have the information about the velocity so it is required that this information is extracted from the dynamic pressure part of the total pressure specified at the inlet.

So I'd like to know how CFX internally separates out the static pressure and the dynamic pressure from a specified total pressure.

sainath.s@tdps.co.in · August 9, 2012, 07:13

The solver takes Static Pressure when there is an outflow and Total pressure when there is an inflow.

P abs = P ref + P stat

The static pressure is calculated in such a way that the boundary remains closed meaning there is no outflow at an inlet.

Secondly, Total pressure at inlet and Static pressure at outlet is very sensitive to the initial guess. For example in the case of turbo machines,when such a condition is used and no velocity magnitude is specified, then the solver takes half of the rotational angular velocity over the boundary as this is reasonable guess to calculate velocity triangles and results a magnitude of zero for stationary domains.

More information is provided in cfx solver modeling guide.

August 9, 2012, 06:18	Dynamic pressure from the total pressure specified	#1
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 18	Could some one please let me know how does CFX compute / separate the static pressure and dynamic pressure when a total pressure is specified at an inlet. Because I suppose that in a problem where a total pressure is specified at the inlets and static pressure at outlets, the solver should some how have the information about the velocity so it is required that this information is extracted from the dynamic pressure part of the total pressure specified at the inlet. So I'd like to know how CFX internally separates out the static pressure and the dynamic pressure from a specified total pressure. __________________ Best regards, Santhosh.

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August 9, 2012, 07:13		#2
sainath.s@tdps.co.in New Member Sainath Join Date: Mar 2012 Posts: 27 Rep Power: 14	The solver takes Static Pressure when there is an outflow and Total pressure when there is an inflow. P abs = P ref + P stat The static pressure is calculated in such a way that the boundary remains closed meaning there is no outflow at an inlet. Secondly, Total pressure at inlet and Static pressure at outlet is very sensitive to the initial guess. For example in the case of turbo machines,when such a condition is used and no velocity magnitude is specified, then the solver takes half of the rotational angular velocity over the boundary as this is reasonable guess to calculate velocity triangles and results a magnitude of zero for stationary domains. More information is provided in cfx solver modeling guide.