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-   -   Why is my fluent simulation giving Cp values above 1??? (http://www.cfd-online.com/Forums/main/74115-why-my-fluent-simulation-giving-cp-values-above-1-a.html)

wils March 24, 2010 16:01

Why is my fluent simulation giving Cp values above 1???
 
hello to everyone on the forum Im a newbie!! can anyone help??

I have recently carried out some fluent simulations of an aerofoil in a wind tunnel.
details; 2D steady flow simulation
standard k-epsilon turbulence model with standard wall functions
pressure correction technique simple algorithm
disecretisation
pressure, second order
momentum, second order upwind
turbulent kinetic energy, first order upwind
turbulent dissipation rate, first order upwind

inlet is a pressure inlet, outlet right hand wall is pressure outlet zero gauge pressure. aerofoil is given wall boundary conditions.

the simulation agrees with experimental results when the aerofoil is set at zero incidence but with higher incidences around 10 degrees the Cp value goes above 1 which cannot be correct...

Does anyone have any idea why this is occuring??
thanks

agd March 24, 2010 16:23

Are you sure you're not computing -Cp?

wils March 24, 2010 16:40

well I was computing Cp values over the aerofoils top and bottom surfaces using the static pressures that the simulation gave, for comparisson to the Cp values calculated from experimental results.

So really I am asking why would the simulation find static pressures at the leading edge of the aerofoil that are greater than the inlet pressure (total pressure)???

pavitran March 26, 2010 10:12

Hi
 
The Cp values can be more than 1 for compressible flows.

1. I guess the flow in your simulation is incompressible. Take correct inlet velocity(V) value, for computing Free stream Dynamic Pressure(0.5*density*V^2).


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