A review of scale effects in unsteady aerodynamics

The importance of scale effects is recognised generally in steady aerodynamics but is often ignored in unsteady aerodynamics. An attempt is made to remedy this situation by the compilation of a review of information on the influence of Reynolds number from a wide range of unsteady aerodynamic tests, with particular reference to wing flows. The unsteady tests considered are buffet and buffeting, dynamic tests of aerofoils and wings, pressure measurements, oscillatory control surface derivatives, and stability derivatives.

The review suggests that for the usual recommended model conditions with fixed transition, scale effects are small for fully-attached or well-separated flows, but may be large close to incipient separation. With fixed transition extrapolation from model to full scale Reynolds numbers is usually possible. In contrast, with free transition scale effects can be large for both attached and separated flows.

Much more research is needed into the magnitude of scale effects on unsteady flows at transonic speeds. Some test cases for the prediction of scale effects in unsteady aerodynamics are suggested. This review combines material presented by the author in Paper 3.4.1 ICAS-90 Proceedings (Stockholm) and Paper 27 AGARD CP 507 October 1991 (San Diego).