Measuremens of Wall Shear-Stress in Skewed Turbulent Boundary Layer on a Ratating Cylinder

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This research aims to measure the wall shear stress in the turbulent boundary layer with skewed velocity profile on a thin cylinder rotating at high speed in an axial stream. The methods to measure the wall shear stress are those to utilize Laser Doppler Velocimetry, miniature hot-wire probe, wall flow tracer, heat tracer, momentum integral equation, and so forth.In the measurement using the miniature hot-wire probe, I- and V-type probes with tungsten wire of 3 μm in diameter were used, and the rotated hot-wire method was employed for I-type probe. Experiments were made nearly in the whole range of the turbulent boundary layer on the cylinder of 1200 mm in length with no rotation and with rotation at the speed ratio, the ratio of the peripheral velocity of the cylinder to the main flow velocity, equal to one. The wall shear stresses were estimated from applying the buffer-fitting method to the data of the near-wall velocity obtained from these miniature probes. Substituting the wall sh … More ear stresses obtained into the momentum integral equation in the form integrated with respect to the x-direction, the balance of this equation was examined, and it was found that its balance was moderately kept ; the estimated wall shear stresses were fairly reliable. The method to obtain the wall shear stress directly from the momentum integral equation was investigated, and, on the basis of an uncertainty analysis, we had a prospect that if the measurement at one section were repeated more than about ten times an accurate value of the wall shear stress would be estimated.The methods using Laser Doppler Velocimetry are to measure the velocity profile in the vicinity of the wall, and there are roughly two methods. One method is to measure in the rotating system, and to do so it is necessary to incorporate the optical system into the rotating body. We are now ready to make experiment for an ad hoc model of a rotating body. The other is to measure in the stationary frame, and the measuring optical system is manufactured by trial. In a word, the study of the methods using LDV are continued.It is our judgment in this research that there is no advantage in the methods using wall flow or heat tracers unless the accuracy of the wall shear-stress value obtained by these methods is far superior to the one obtained by the other methods, partly because of the difficulty of setting the devices or sensors for these methods on the rotating wall at high speed. Less