THE LADDER PROBE - REVERSE FLOW MEASUREMENTS WITH A HOT-WIRE RAKE

A probe consisting of a ladder-like rake of hot wires was developed in order to facilitate velocity measurements in reverse flow situations. Hot-wire signals obtained by the ladder probe capture a substantial section of the instantaneous velocity profile which includes the point where the change of direction occurs. These signals were processed to obtain the thickness of the reverse flow layer through a procedure which detects the point of zero velocity. The procedure was validated through a conservation-type consistency test, frequency response and periodicity tests, and by comparison with results in the literature. Characterization of a turbulent separated layer is discussed. Three different parameters are used to measure the thickness of the reverse flow region: cross streamwise coordinate of the point of zero average velocity, average coordinate of zero velocity points, and the coordinate of the 50% flow direction (forward or reversed) probability point. Relationships between these parameters and physical interpretation of their relevance to the separated flow field are also discussed.