Development of Dual Film Probe form Dynamic Measutemtn of Wall Shear Stress

点击翻译按钮获取中文摘要

In order to improve the characteristics of glue-on type hotfilm probe for time dependent wall shear stress measutement, a new type of probe arrangement, called dual film probe, have been proposed and its static and bynamic charactersitics have been tested. The inverstigations were performed in the following four step.1. Trial production of dual film probe: Two nickel films were doposited on both sides of a thin polyimid sheet at precisely the same position. The thickness of the polyimid sheet were 100,50 and 25 micrometers and the nickel films have the width of 0.1mm and the length of 1mm and their temperatures are independently controlled by employing two sets of constant temperature anemometers. Upper film is used as a wall shear stress sensor while the lower one is used as a guard to minimize the heat conduction loss into the wall.2. Static test: Test film was glued on the inner surface of the two-dimensinal channel and the telation between the hot-film output voltage and the corresponding wall shear stress evaluated from the longitudinal pressure gradient was determined. The guard film was found oeeficient to minimize the output drift when to wall temperature was changed.3. Dynamic test: The plusatile flow was produced in twodimensional channel and the phase averged wall shear stress and output coltage were compared. It was found that the amplitude degeneration is considerably improved by employing the guard film.4. Numerical simulation: To optimize the film arrangement and the meteral characteriastics, conjugated heat transfer problem was numerically analyzed. The agreement with the mesaured results were only wqualitative, the reason of which was attributed to the negligence of the temperature distribution on the film surface.