Quote:
Originally Posted by JulianEdgar
I don't think that is right. No air is inviscid. None. Inviscid fluid is imaginary - it doesn't exist.
Inviscid airflow is used only to greatly simplify the model of airflow that can be used. That is, it's a 'model trick'.
Wikipedia puts it well (I can give more formal references if anyone wishes. Anderson's books on aerodynamics are good in this regard):
Inviscid flow is the flow of an inviscid fluid, in which the viscosity of the fluid is equal to zero. When viscous forces are neglected, such as the case of inviscid flow, the Navier-Stokes equation can be simplified to a form known as the Euler equation. Using the Euler equation, many fluid dynamics problems involving low viscosity are easily solved, however, the assumed negligible viscosity is no longer valid in the region of fluid near a solid boundary.
In other words, if we're interested in pressures acting on the surface of the body (ie a solid boundary) - and with car aero, that is all that we are interested in - then using inviscid flow models is of no / very little use to us.
|
1) If aerodynamic drag is the concern, the two-dimensional, inviscid-flow modeling will provide enough pressure gradient information to the engineer, to be able to establish whether or not, the specific body under investigation will trigger flow separation at any particular location or not.
2) The decision, whether to advance to the viscous effects calculations or not can be determined right then and there. Go NoGo.
3) This would be the primary value of the 2-D modelling.