Traverse Mechanisms for the Determination of Reynolds Stresses using Hot-Wire Techniques
Artikel i vetenskaplig tidskrift, 1988
Recent developments in boundary layer calculations have raised higher demands on the used turbulence models. To test these models, comparison must be made between the theoretical model and experimentally determined turbulent stresses (Reynolds stresses). Two methods are dominating in this kind of measurements, hot-wire and laser technique seems to be the most widely used method so far.
In the present note the function of two traverse mechanisms, which have been used in hot-wise measurements, are presented. The emphasis of this note is put on the solution of fundamental problems in connection with the movements of the hot-wire, and not on showing details and dimensions of the traverse mechanisms.
The first traverse mechanism to be described has been used in a hot-wire technique, which is normal to the surface. When measuring all six different Reynolds stresses at one point of a profile this technique usually demands measured values from two probes.
The second traverse mechanism has been used in the cross- as well as triple-wire technique. In the cross-wire method the hot-wire probe is traversed step by step through the boundary layer and rotated. However, in this case the rotated is performed around an axis, whish is parallel to the surface. Since the hot-wire probe in this case contains two hot-wires, all six turbulent stresses may be determined using only one probe. This triple-wire probe contains three hot-wires, and thus, only a translation of the probe normal to the surface is needed for the determination of the complete Reynolds stress tensor.