coeffiecient of pressure

[jo...@geocities.com]

Hello, Now I am making a lot of calculation with the coeffient of
pressure and I was reading the book "theory of wing section", and i
haven't notice that this coeffiecient can be obtain by the simple
relantion of (v/V^2). In the book the also use other relation v/V and
deltava/V what is the diferent between then. Can anybody explain why
this, and where this equation derivate, and what is the meaning of each
variable.

Joel Guerrero

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[David R. Kuechenmeister]

I guess the right answer is that if you are looking at the wing section
book, you probably should go out and find an aerodynamics book to
complement its content. "Theory of Wing Sections" should have a table of
symbols somewhere in the book.

The direct answer is that the pressure coefficient comes from Bernoulli's
equation, p - p_0 = q_0 - q, where the _0 subscript means freestream.

This equation can be rearranged to give Cp = 1-(q/q_0) = 1-(v/v_0)^2 .

In the above equations, q = 0.5*rho*v^2, ie. the dynamic pressure, and
v is velocity. Unsubscripted, it refers to the local velocity and I've
already defined the _0 subscript.

That's about as much as I can give you about the different forms of the
pressure coefficient. I think what A&VD do for the v/V and deltav/V terms
is to define
1-Cp = S, where S can be calculated with the basic thickness distribution
and mean-line shapes for an airfoil. The deltav/V_0 term is the design load
distribution ( difference in upper and lower pressures ) for the mean
line. The equations that you would find in a aero book, allow you to
determine pressure and velocity distributions for different thickness
airfoils in the same series.

I wouldn't mind faxing a couple pages that describe the process, if that's
what you would like to see.

Regards,

--
David R. Kuechenmeister
Georgia Tech Research Institute
Atlanta,GA 30332-0853
mailto:David.Kuec...@gtri.gatech.edu Voice: (770)528-7738