| Research Abstract |
This research project aims to establish all effective new control method of separation, which manages the critical performance of various fluid flow devices and machines, especially to develop an active control method that is used properly depending on the external condition. For this purpose, we have adopted a vortex generator jet method, which is to generate streamwise vortices by pitched and skewed jets issued from the wall, considering the feature that a jet has the high potential of adjustability. From the present basic research planned for a two-years program, we can have the following interesting results
(1) Distribution of backflow-fraction is a useful measure to specify one of characteristics of separating (low in a diffuser. Here are proposed two kinds of the measurement methods, a X-type hot wire and a split film sensor. Usage of the latter will generally be regarded as convenient, if the measurement will be made using a smaller-size test-rig.
(2) Although a streamwise vortex
… More
induced by a VGJ (vortex-generator-jet) is weaker than that by a 501i(I vortex generator, The row of streamwise vortices sufficiently applicable to control separation in a diffuser is observed in the boundary layer, providing that the velocity ratio of jet to freestream is around 2.
(3) As for a typical example, the following VGJ is applicable to suppress the separation observed in a conical diffuser having the divergence angle of 18 deg and the exit-to-inlet area ratio of 2.56, and the pressure recovery coefficient is improved from 0.4 to 0.6 : Pitch-angle = 30 deg, Skew-angle = 90 deg, Jet-dia. = 0.048 D, The number-of-jets = 8, Velocity-ratio = 2.
(4) The decay of a streamwise vortex in a two-dimensional channel is fairly predicted by the numerical analysis based on the Reynolds-Averaged Navier-Stokes equation with the standard k-epsilon turbulence model.
(5)In the case of a downstream diffuser, it is effective to detect the magnitude of velocity fluctuation in a freestream at the diffuser inlet as the signal for the active control Less
|
