The effect of circumferential single grooved casing treatment on the stability enhancement of NASA Rotor 37 has been examined with computational fluid dynamics analysis. Stall inception mechanism of Rotor 37 is presented first with principal focus on the tip leakage flow behavior, passage blockage, and the vortical flow structures. Detailed observation showed that the combined interaction of the stagnated flow of tip leakage vortex breakdown and the jetlike leakage flow from the midchord region leads to the blade tip-initiated stall inception. The result of numerical parametric study is then demonstrated to show the effect of varying the axial location and the depth of a circumferential single groove. The evaluation based on stall margin improvement showed a higher potential of deeper grooves in stability enhancement, and the optimal position for the groove to be located was indicated to exist near the leading edge of the blade.
The effect of circumferential single grooved casing treatment on the stability enhancement of NASA Rotor 37 has been examined with CFD analysis. Stall inception mechanism of Rotor 37 is presented first with principal focus on the tip leakage flow behavior, passage blockage, and the vortical flow structures. Detailed observation showed that the combined interaction of the stagnated flow of tip leakage vortex breakdown and the jet-like leakage flow from the mid-chord region leads to the blade tip-initiated stall inception. The result of numerical parametric study is then demonstrated to show the effect of varying the axial location and the depth of a circumferential single groove. The evaluation based on stall margin improvement showed a higher potential of deeper grooves in stability enhancement, and the optimal position for the groove to be located was indicated to exist near the leading edge of the blade.
This study investigates experimentally and numerically unsteady flow fields in an axial compressor operating at high-flow rate in order to understand the flow structure in the stator row operating at windmill condition. The experimental and numerical data are compared by time- and phase-lock-averaged techniques. Additionally, unsteady vortex structure is investigated by numerical technique. At windmill condition, the incidence angle to the stator row becomes extremely negative. Therefore, large separation occurs near pressure surface in the stator passage. The experimental and numerical results indicate that a large vortex is generated in the separation area. According to the numerical results, part of the vortex migrates downstream, and the vortex produces blockage of the main stream of the stator passage. Therefore, net flow area in the stator passage becomes small so that the flow between the vortex and suction side of stator vane is accelerated. As a result, the total pressure deterioration is generated in the stator passage because the high speed flow and the vortex cause high shear.
Electrochemical machining (ECM) is an advanced machining technology. It has been applied in highly specialized fields such as aerospace, aeronautics, and medical industries. However, it still has some problems to be overcome. The efficient tool design, electrolyte processing, and disposal of metal hydroxide sludge are the typical issues. To solve such problems, computational fluid dynamics is expected to be a powerful tool in the near future. However, a numerical method that can satisfactorily predict the electrolyte flow has not been established because of the complex nature of flows. In the present study, we developed a multiphysics model and the numerical procedure to predict the ECM process. Our model and numerical procedure satisfactorily simulated a typical ECM process for a two-dimensional flat plate. Next, the ECM process for a three-dimensional compressor blade was simulated. Through visualization of the computational results, including the multiphase flow, and thermal and electric fields between the tool and the blade, it is verified that the present model and numerical procedure could satisfactorily predict the final shape of the blade.
Stall characteristics and stall cell behavior in a linear cascades system of a single stage axial compressor are presented by applying a numerical analysis of compressible N-S equations. The system consists of a rotor and a stator, where flow is assumed to be periodic over six blades and ten vanes respectively. Although the number of blades and vanes per period is much less than that in the real-rig, and the analysis is conducted in a laminar viscosity mode, computed stage performance from normal operation to deep stall agrees fairly well with experimental data. In deep stall, rotor cell propagates in linkage with stator cell at a computed speed of 65 % of the rotor speed. This speed is considerably close to the measured value of 55 %. Stall cell propagation is discussed on flow patterns showing stall development, stall induction in the follower blade and interaction between the rotor and stator.
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