شبيه‌سازي عددي جريان در جداره‌ي بهبود‌دهنده با پره هاي به عقب كشيده شده به‌منظور افزايش حاشيه‌ي امن واماندگي در كمپرسورهاي جريان محوري

Numerical Simulation of Vane-Recessed Casing Treatment for Stall Margin Improvement in an Axial Flow Compressor

در اين نوشتار، شبيه‌سازي جريان عبوري از كمپرسور جريان محوري با استفاده از جداره‌ي بهبود‌دهنده‌ي به عقب كشيده شده با پره هاي هادي بررسي مي‌شود و نتايج حاصل از آن با نتايج تجربي به دست آمده از آزمايشات تجربي مورد مقايسه قرار مي‌گيرد. فرايند شبيه‌سازي مبتني بر حالت پايدار و همراه با دقت بالاست و از منظر اعتبارسنجي با داده هاي تجربي سازگاري قابل ملاحظه‌يي را نشان مي دهد. نتايج نشان مي دهند كه با كاربرد جداره‌ي بهبود‌دهنده‌ي به عقب كشيده شده، پايداري سيستم به‌ميزان قابل ملاحظه‌يي بهبود و حاشيه‌ي امن واماندگي افزايش يافته است. ساختارهاي گوناگون از منظر عدم پوشش وتر محوري جز دوار نشان مي دهد كه جداره‌ي بهبود‌دهنده با عدم پوشش 33/33‌% داراي بهترين بهبود در حاشيه‌ي واماندگي و بهترين عملكرد در راندمان كلي به كلي، كلي به استاتيك، و با عدم پوشش 63/63‌% داراي بهترين مقدار ضريب بيشينه‌ي افزايش فشار كلي به كلي است.

In this paper the numerical simulation of a vane-recessed casing treatment was performed. The vane-recessed casing treatment largely optimizes the stability of an axial flow compressor. The main purpose of the current investigation was to compare the stall margin improvement as well as the stable and extended operation achieved from the experimental work and those resulted from the simulations. The stability of a compressor is highly affected by the unsteady aerodynamic characteristics, namely, rotating stall and surge. These instabilities reduce the life duration and performance of the compressor. When the mass flow rate is reduced to an amount lower than the design value then the stable flow may become unstable. This phenomenon would appear as rotating stall which in severe condition may lead to surge. Occurrence of rotating stall is usually accompanied with the significant reduction of the efficiency and pressure rise coefficient, which would provide a lower performance. The incidence of surge may lead to cessation of the mass flow rate which may lead to the complete breakdown of the compressor operation. The current numerical study utilized a steady state simulation of a vane-recessed casing treatment, while different rotor blade axial cord exposures were tested. These different configurations of rotor blade exposures were 23.23%, 33.33%, 43.43%, 53.53%, 63.63% and 73.73%. Among the rotor blade exposures mentioned above, the 33.33% axial blade cord exposure casing treatment showed the best stall margin improvement. Furthermore, in term of total to total overall efficiency the 33.33% rotor blade axial exposure provided the best performance among the different casing treatments. In order to validate the results obtained from the numerical simulation, the results were compared to those achieved from the experimental work. This comparison indicates that there are good agreements between the experimental and numerical data. The results demonstrate that the application of a vane-recessed casing treatment as a passive stall control technique enhances the stall margins and system stability.