Abstract:Stall recovery process for performance enhancement of an axial compressor has been experimentally carried out using air injection at its rotor blade row tip region. Twelve air injectors had been mounted evenly spaced around the compressor casing upstream the rotor blade row. Instantaneous flow velocities at various radial and circumferential positions were measured simultaneously utilizing hot wire anemometry. These unsteady results, separately presented in frequency and time domains, provided to distinguish s… Show more
“…It can be deduced from this figure that the maximum difference between the present numerical results with each of the experimental results is about 12%, which seems appropriate. Figure 7 Comparison of performance curves between present results and available experimental data 8 , 10 . …”
Section: Numerical Simulation Procedures and Boundary Conditionsmentioning
confidence: 91%
“…To validate the numerical results, performance curve of the plane case (i.e., no treatment) in terms of the total pressure rise coefficient versus the flow coefficient are compared with those of Inoue et al 10 and Taghavi et al 8 which are carried out experimentally. These results are shown in Fig.…”
Section: Numerical Simulation Procedures and Boundary Conditionsmentioning
confidence: 99%
“…This regional beneficial effect can extend towards the blade root region, and as a result, can improve the aerodynamic performance of the blade, nearly all along its span. Taghavi et al 8 experimentally controlled the blades tip leakage flow in a low speed axial compressor by applying very low rate of air injection via 12 nozzles mounted evenly spaced around the casing circumference. They observed, through smoke and tuft flow visualizations, that the beneficial effects of proper air injection at the blades tip region remarkably extends nearly along the whole blade span.…”
Blades tip leakage flow structure in axial compressors has dominant effects on flow stability and losses. Accordingly, in the present study, three different ideas are introduced for alleviation of undesirable effects of the blades tip leakage flow. These ideas utilize circumferential tape, S-shape nozzle and natural aspiration slot, all imposed upstream the rotor blades row. The method of investigation is based on numerical simulation of the governing flow field. Results, in terms of the flow field structure and performance curves are compared with those of the untreated case. Final results, showed that the natural aspiration idea works better than the other ones. In comparison to the plane case, it is accompanied by augmentation of 3.5% in the total pressure ratio and 3% in the surge margin. It was also found that the mass flow rate passing through the blades row tip gap has increased by 2.33 g/s in the natural aspiration case.
“…It can be deduced from this figure that the maximum difference between the present numerical results with each of the experimental results is about 12%, which seems appropriate. Figure 7 Comparison of performance curves between present results and available experimental data 8 , 10 . …”
Section: Numerical Simulation Procedures and Boundary Conditionsmentioning
confidence: 91%
“…To validate the numerical results, performance curve of the plane case (i.e., no treatment) in terms of the total pressure rise coefficient versus the flow coefficient are compared with those of Inoue et al 10 and Taghavi et al 8 which are carried out experimentally. These results are shown in Fig.…”
Section: Numerical Simulation Procedures and Boundary Conditionsmentioning
confidence: 99%
“…This regional beneficial effect can extend towards the blade root region, and as a result, can improve the aerodynamic performance of the blade, nearly all along its span. Taghavi et al 8 experimentally controlled the blades tip leakage flow in a low speed axial compressor by applying very low rate of air injection via 12 nozzles mounted evenly spaced around the casing circumference. They observed, through smoke and tuft flow visualizations, that the beneficial effects of proper air injection at the blades tip region remarkably extends nearly along the whole blade span.…”
Blades tip leakage flow structure in axial compressors has dominant effects on flow stability and losses. Accordingly, in the present study, three different ideas are introduced for alleviation of undesirable effects of the blades tip leakage flow. These ideas utilize circumferential tape, S-shape nozzle and natural aspiration slot, all imposed upstream the rotor blades row. The method of investigation is based on numerical simulation of the governing flow field. Results, in terms of the flow field structure and performance curves are compared with those of the untreated case. Final results, showed that the natural aspiration idea works better than the other ones. In comparison to the plane case, it is accompanied by augmentation of 3.5% in the total pressure ratio and 3% in the surge margin. It was also found that the mass flow rate passing through the blades row tip gap has increased by 2.33 g/s in the natural aspiration case.
“…This rotor has already been tested experimentally by Inoue 28 . www.nature.com/scientificreports/ Taghavi et al 29 have already conducted many tests on this rotor blades row in a low speed axial compressor test-rig located at the Aerodynamic and Compressible Turbomachine Research Laboratory of the Iran University of Science and Technology (IUST-ACTLab). The layout of this test-rig is shown in Fig.…”
This paper presents results of aerodynamic enhancement of axial compressors utilizing optimum natural aspiration through a circumferential slot made within the casing wall upstream the rotor blades row. The method of investigation is based on numerical simulation of flow field. Geometries of the slot walls were optimized to find the maximum stall margin and pressure ratio of the compressor. The optimum case is accompanied by boosting more momentum within the blades tip region through the slot. Consequently, tip leakage vortex flow weakens and compressor stability margin increases. Final results showed that in comparison to the untreated casing, the optimum geometry of the slot causes the total pressure ratio and stall margin to increase by 4.2% and 3%, respectively. This state-of-the-art technique is simple and economic which can be easily implemented in practical cases while the compressor is exposed to commencement of flow instabilities in the forms of the rotating stall or surge phenomena.
Discrete tip injection is an effective method to enhance stability of compressors. This study compares the effects of injection parameters on compressor performance and underlying mechanisms in two different compressors. The transonic compressor is studied using unsteady simulations and the subsonic compressor is mainly investigated with experiment. Results show that tip injection improves stable operating range by 35.6% and 77.9% for the transonic compressor and subsonic compressor, respectively, without decreasing compressor efficiency. The effects of circumferential coverage percentage and injector throat height on compressor stability are similar in the two compressors when the injection velocity is double the velocity of main flow. The optimal injector throat height which is normalized by the tip clearance size is the same for the two compressors, and the best circumferential coverage percentage for the subsonic compressor is lower than that in the transonic compressor. For the two compressors, the adaption of the main flow to the discrete tip injection is unsteady, and the hysteresis effect that the recovery of tip blockage lags behind the recovery of tip leakage vortex accounts for the improved stability using partial coverage of injection. The injection efficiency, which is defined to quantify the improved quality of the flow field in the injection domain, is proven to determine the stall limits by studying the effects of several injection parameters. The guidelines built in the subsonic compressor can be used in the transonic compressor to design tip injection, but the optimal values of some injection parameters should be reconfirmed.
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