Subsonic MHD-diffuser performance with high blockage

Abstract

Diffuser performance with high blockages is analyzed by a two-dimensional turbulent-flow model. This model is used to analyze the performance of simple two-dimensional, plane-walled diffusers and also of threedimensional diffusers up to and beyond the blockage limits for which previous analytical or experimental data are available. The effects of important design parameters on diffuser performance are investigated. The parameters considered are the blockage, divergence angle, Mach number, aspect ratio, and wall-to-freest ream temperature ratio. The first two parameters affect the diffuser performance significantly; the other parameters influence the performance only slightly. Results obtained from the subject model agree reasonably well with the available experimental data. The diffuser design of the U-25 facility is analyzed and the analysis predicts a pressure recovery of 0.49, which agrees very well with the measured experimental value of approximately 0.48, obtained from a small-scale model. Nomenclature= geometric cross-sectional area of diffuser, A = H> W = effective flow cross-sectional area of diffuser, A ef t=(H-2d H *)(W-2d w *) = aspect ratio , ^ = HI W -diffuser blockage parameter, B s-J -(A cff /A) = static pressure recovery coefficient, Cp -(Pexit ~ Anlet V(Po ~ P ) inlet > where p 0 is evaluated at the centerline of diffuser = geometrical height of diffuser (in the y direction) = length along the diffuser = Mach number (at the diffuser centerline) = mass flow rate -static pressure = longitudinal velocity component -geometrical width of diffuser (in the z direction) = physical boundary-layer thickness = physical boundary-layer displacement thickness, A A eff

Inflow Disk Generator for Open-Cycle MHD Power Generation

“…31 ' 32 An estimate of the reduction in pressure recovery of simple twodimensional, plane-walled diffusers was given by Doss. 31 It was shown that the pressure recovery decreases from C PR = 0.7 at zero blockage down to C PR =0.48 at 18% blockage. This indicates that the pressure recovery of diffusers for baseload linear generators, which operate with even higher inlet blockages, will probably be about C PR =0.4-0.45.…”