An experimental and numerical study of the transonic flow through a linear compressor cascade with endwalls was conducted. The cascade with a low aspect ratio of 1.34 was tested at an inlet Mach number of 1.09 and a Reynolds number of 1.9×106. Detailed flow visualizations on the surfaces and five-hole probe measurements inside the blading and in the wake region showed clearly a three-dimensional boundary layer separation on the blade surface and the sidewall, and a severe corner stall induced by a strong 3-D shock system at blade passage entrance. The experimental data have been used to validate and improve the 3-D Navier-Stokes code TRACE. Results showed an excellent resolution of the complex flow field. Surface pressure distributions on the entire blade surface and the endwalls, flow angle and total pressure contours within the blade passage and the wake are compared with the experimental results. An analysis of the secondary flow of this highly staggered cascade did not show the classical corner vortex. Instead, a severe flow deviation and partly reverse flow near the walls is seen. The flow solver helped to identify a weak ring vortex that originates from the passage sidewall. Surface oil flow pictures on the blade contour and the sidewall are in qualitatively good agreement to numerical surface streaklines. A considerable improvement of the numerical results could be achieved by a gradual grid refinement, especially in the corner region and by successive code development.
An experimental and numerical study of the transonic flow through a linear compressor cascade with endwalls was conducted. The cascade with a low aspect ratio of 1.34 was tested at an inlet Mach number of 1.09 and a Reynolds number of 1.9×106. Detailed flow visualizations on the surfaces and 5-hole probe measurements inside the blading and in the wake region showed clearly a 3-dimensional boundary layer separation on the blade surface and the sidewall, and a severe corner stall induced by a strong 3D shock system at blade passage entrance. The experimental data has been used to validate and improve the 3D Navier-Stokes code TRACE. Results showed an excellent resolution of the complex flow field. Surface pressure distributions on the entire blade surface and the endwalls, flow angle and total pressure contours within the blade passage and the wake are compared with the experimental results. An analysis of the secondary flow of this highly staggered cascade did not show the classical corner vortex. Instead, a severe flow deviation and partly reverse flow near the walls is seen. The flow solver helped to identify a weak ring vortex that originates from the passage sidewall. Surface oil flow pictures on the blade contour and the sidewall are in qualitatively good agreement to numerical surface streaklines. A considerable improvement of the numerical results could be achieved by a gradual grid refinement especially in the corner region and by successive code development.
A transonic compressor rotor cascade designed for an inlet Mach number of 1.09 and 14 degrees of flow turning has been redesigned for higher loading by an increased pitch-to-chord ratio. Test results, showing the influence of inlet Mach number and flow angle on cascade performance are presented and compared to data of the basic design. Loss-levels of both, the original and the redesigned higher loaded blade were identical at design condition, but the new design achieved even lower losses at lower inlet Mach numbers. The computational design and analysis has been performed by a fast inviscid time-dependent code coupled to a viscous direct/inverse integral boundary-layer code. Good agreement was achieved between measured and predicted surface Mach number distributions as well as exit-flow angles. A boundary-layer visualization method has been used to detect laminar separation bubbles and turbulent separation regions. Quantitative results of measured bubble positions are presented and compared to calculated results.
The outlet conditions of supersonic compressor rotors designed for very high total pressure ratios can be highly supersonic (impulse rotors). Then the following stator blade row has to build up high static pressure ratios at supersonic inlet conditions. This paper describes part of a research work which should answer, if it is at all possible to realize such high static pressure ratios in a cascade. Cascades with convergent-divergent blade passages were designed and optimized by boundary layer calculations. In a first step no flow turning was incorporated in the blade sections. A three-shock-type cascade was found to be an optimum design The wind tunnel measurements resulted in static pressure ratios of the order of 6 and total pressure ratios of 0.77 at inlet Mach numbers of 2.2. In a second step the flow turning to axial direction was realized. For that two types of cascades were built and tested. One was a tandem type cascade and the other a single row cascade. The experiments at inlet design conditions resulted in static pressure ratios of the order of 6.5 and total pressure ratios of 0.72.
Tests of transonic compressor cascades require special measuring techniques to determine the inlet flow angle around sonic inlet flow conditions. One of the main requirements for these methods is the ability to adjust the inlet flow angle during the test to a prescribed value. A method has been successfully applied that relies on theoretically determined suction surface velocities. The described method was applied in testing cascades at inlet Mack numbers between M1 = 0.75−1.18. The test results confirmed the practicability of this method.
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