Scale Effects at High Subsonic and Transonic Speeds, and Methods for Fixing Boundary-Layer Transition in Model Experiments

摘要

The major scale effects at high subsonic and transonic speeds arise from differences between the conditions under which laminar and turbulent boundary layers separate, and in how they behave after separation. For turbulent boundary layers, these conditions and behaviour do not vary greatly as the Reynolds number is changed and in many examples, it has been shown that they are similar for the turbulent layers that occur naturally at high Reynolds number and for boundary layers in which transition to turbulent flow is fixed artificially. The scale effects arising in wind-tunnel tests made at low Reynolds number may, therefore, often be minimized by fixing transition to turbulent flow by introducing an artificial disturbance such as that produced by excrescences attached to the surface. The fact that the effects of separation are often less severe for laminar layers than for the turbulent layers that are likely to be encountered at full scale, makes it all the more important to do this whenever possible.