چكيده به لاتين
Range of stable operation in an axial flow compressor is limited with the occurrence of aerodynamic instabilities, namely stall and surge. These aerodynamic instabilities could be controlled or to be delayed by using active or passive control techniques. One of the suitable passive stall control techniques, which could be used to delay stall inception is the casing treatment in axial flow compressors. The current thesis has the aims of study the effect of vane recessed casing treatment on the operation of an axial flow compressor. The geometry of the inlet guide vanes blade row together with one low speed stage of compressor that contains one row with 38 rotor blades and one row with 37 stator balde in accompanied by bellmouth and outle areas, has been modeled. This configuration has been investigated experimentaly by Dr. Mohhamad Akhlaghi at Cranfield Univerty. The numerical investigation also conducted in Iran Uniuvrsity of Sience and Technology. The numerical outcomes validated with the experimental results. Nearlly good agreements were found from the experimentals and numerical results.
Numerical investigation has been conducted for two different geometric configuration, namely semi-tubular passage and semi-circular passage vane-recessed casing treatments. Tubular passage configuration included seven rotor blade tip axial chord exposures of 23.2%, 33.3%, 43.4%, 53.5%, 63.6%, 73.7% and 83.8%. The mentioned exposures were studied using 120 casing treatment guide vanes. Only four rotor blades tip axial chord exposure of 23.2%, 43.4%, 73.7% and 83.8% were studied in semi-circular passage configuration. The latter were more investigated by four constructions of 40, 70, 100 and 120 number of inlet guide vanes inside the casing treatment.
All the studies based on number of vanes conducted in the semi-circular passage casing treatment studies, were also further evaluated for the semi-tubular passage casing treatment configurations. From the perspective of pressure ratio, semi-tubular passage configuration with 43.4% rotor balde tip axial chord exposure and 40 number of vanes has provided the best value for the overall total-to-total pressure ratio of 1.011and total-to-static pressure ratio of 1.006.
However, from the perspective of pressure rise coefficient, semi-tubular passage configuration with 83.8% rotor blade tip axial chord exposure and 40 number of vanes, has shown provided the best value for total-to-total pressure rise coefficient 0.378 total-to-static pressure rise coefficient 0.221.
The highest values of the overall efficiency for semi-tubular passage casing treatment based on the total-to-total pressures calculated as 0.691 and based on the total-to-static pressures was found 0.335, for the rotor blade tip axial chord exposure of 23.2% in accompanied with 100 number of vanes inside the casing treatment. It is evident that from the perspective of maximum efficiency, the 23.2% of rotor blade tip axial chord exposure has the highest overall total-total efficiency.
Comparisons of the two configurations mentioned above, the semi-circular passage treated casing provided the highest value of the overall total-to-total pressure ratio, which were belong to the 43.4% rotor tip axial chord exposure and 40 number of vanes inside the casing treatment. From the perspective of overall total-to-total pressure rise coefficient, the semi-circular passage configuration with 40 number of vanes and 43.4% rotor tip axial chord exposure were the best configuration. Also in the perspective of the overall total-to-total efficiency, semi-tubular passage configuration with 53.5% rotor tip axial chord exposure and 120 number of vanes provided the most desirable amount. The maximum value for stall margin improvement based on the corrected mass flow rate was calculated as 38.24% and it was belonged to the semi-circular passage casing treatment configuration with 83.8% rotor blade axial chord exposure and with 100 number of vanes inside the casing treatment.
