INVESTIGATION OF PERFORATED CONVERGENT-DIVERGENT DIFFUSERS WITH INITIAL BOUNDARY LAYER

An investigation of mass-flow end total-pressure recovery characteristics of perforated convergent-divergent supersonic dif-fueers operating with initial boun&ary layerhas been conducted at a Mach number of 1.90 at the KACALewis laboratory. mundaqiayer wss established by use of cylindrical inlets, approximately 2, 3, and 4 inlet diameters in length, affiXed. to diffUS8m that ranged in contraction ratio from 1.40 to 1.59. Peak total-pressure recovery and supercritical r8cov8r8d mass flow were decreased a maximum of approIimat8l.y 2 percent by the use of the longest inlets. Combinations of cylindrical inlets, perforated supersonic dif-fusers, and a subsonic diffuser were evaluated 8s simulated wind' turneti having s8coPa throats. comparisons mad8 with noncontracted configurations of similar scale i&icated operating power reduc-tions of at least 25 percent baaed on a conservative approximation to the Dower required for bleeding mass flow thro&h the diffuser perforations. Bmse reductions were accomqlished at operating total-pressure ratios of lea8 than 1.2 and with removal through the perforations of lesa than 8 percent of the msas flow of the eimulated test seotions. Perforated colrvergentaivergent supersonic Biffwers with their high tbtal-preesure recoveriee have pOsSibi8 application as aircraft engine difTuaer8 ad tind-tunnel eecond throats. rn the tunnel application, they allow contracted fixed-1 oonfigura-tions that avoia stsrting limitations & comMn8 low operating ' pressure ratios with excellent flow stability. Characteristics of.. perforated diffusers for conditions of negligible boundary layer. at the diffuser inlets are reporte & in references 1 and 2. For win&-tunnel applications the diffusers will encounter appreciable m entrant boundary leyer. A limited investigation has therefor