# Can we model flow over an airplane wing with incompressible flow equations?

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June 29, 2019, 03:36
Can we model flow over an airplane wing with incompressible flow equations?
#1
Senior Member

Join Date: Jan 2018
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Hi,
As you know, airplanes have an average velocity of 750 km/h which means they have a Mach number of about 0.6.
According to NASA:
Quote:
 For low speed, or subsonic conditions, the Mach number is less than one, M < 1 and the square of the Mach number is very small. Then the left hand side of the equation is very small, and the change in density is very small. For the low subsonic conditions, compressibility can be ignored.
Does it mean that I can neglect the effect of compressibility and use incompressible equations to simulate the flow over the airfoil using LES or etc?
Is the solution reliable?
How much error can be generated?

June 29, 2019, 03:52
#2
Senior Member

Filippo Maria Denaro
Join Date: Jul 2010
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Quote:
 Originally Posted by KevinSpears Hi, As you know, airplanes have an average velocity of 750 km/h which means they have a Mach number of about 0.6. According to NASA: Does it mean that I can neglect the effect of compressibility and use incompressible equations to simulate the flow over the airfoil using LES or etc? Is the solution reliable? How much error can be generated?

It depends on the flow problem. Check the inlet Mach condition but consider that the flow accelerate along the airfoil and the Mach can reach higher values. If transonic effects can be disregardable, the incompressible formulation could be quite acceptable. A value of the inlet Mach number greater than 0.3 would address towards a compressible formulation.

 Tags airfoil, airplane, les