مدل‌سازي صفر‌بعدي كمپرسور محوري و گريز از مركز يك توربوجت و ارز‌يابي آن به‌كمك نتايج آزمايش‌هاي تجربي

ZERO DIMENSIONAL MODELING OF AXIAL AND CENTRIFUGAL COMPRESSORS OF A TURBOJET AND VALIDATION BY TEST RESULTS

در مراحل مختلف طراحي يك كمپرسور لازم است مدل‌سازي آن صورت پذيرد تا قبل از ساخت و انجام آزمايش‌هاي تجربي، رفتار‌‌سنجي كمپرسور با دقت مناسب امكان‌پذير ‌شود. يكي از روش‌هاي مدل‌سازي رايج و كارا در مراحل مختلف طراحي، شبيه‌سازي صفر‌بعدي با استفاده از روش مقياس با ضريب ثابت است. اين روش در سرعت‌هاي نزديك نقطه‌ي طرح جواب قابل قبولي مي‌دهد؛ ولي در نقاط خارج طرح و با فاصله گرفتن از آن، خطا سير صعودي دارد و در جاهايي غيرقابل قبول مي‌‌شود. در اين نوشتار براي رفع اين مشكل روش جديدي توسعه داده مي‌شود كه در آن به‌جاي به‌كارگيري ضريب ثابت در روش مقياس، از ضريب متغير استفاده مي‌شود. اين ضريب متغير براساس مطالعه روي نتايج آزمون چند نوع كمپرسور حاصل مي‌‌شود. در اين نوشتار با استفاده از اين روش جديد، رفتار يك كمپرسور محوري و يك كمپرسور گريز از مركزِ يك نوع توربوجت مدل‌سازي و ارايه مي‌شود. به‌منظور ارز‌يابي نتايج مدل و مقايسه‌ي آن با نتايج تجربي، يك‌سري آزمايش‌هاي سازمان‌‌يافته در آزمايشگاه توربين گازي دانشگاه صنعتي شريف صورت گرفته است. مقايسه‌ي نتايج حاصل از مدل‌سازي با نتايج تجربي نشان از دقت قابل قبول مدل دارد.

The conceptual design phase of a gas turbine compressor, in which parametrical studies are of more attention, demands a general but comprehensive model. Accordingly, simulation of an engine compressor performance not only reduces the cost and risk in the development and manufacturing phases, but becomes a tool to inspect the engine compressor performance and functionality during the engine compressor working life. Therefore, a suitable model with acceptable precision, which is empirically validated, will help to give a quick estimate of engine compressor performance. Dimensionless modeling is one of the prevalent and applicable modeling methods for different stages of gas turbine compressor design. This methodology is geometry independent and, by supplying major gas turbine compressor parameters, provides a precise model to predict engine compressor performance in a wide operational range. This model provides a fairly accurate estimate of the engine compressor function in preliminary phases of conceptual design. As a result, before getting through comprehensive analysis, costly manufacturing and tests, an acceptable prevision of engine compressor functionality will be at hand. Many recent methods, including genetic algorithms and fuzzy logic, require the engine compressor to be tested and, thereby, interpolating or extrapolating to forecast the rest of the range. But the technique presented here develops a model without operational testing of the engine compressor. A custom dimensionless technique is a scaling method with a constant coefficient. In this method, using the on-design points of a gas turbine compressor, and by scaling a standard performance map, the corresponding engine compressor performance map is achieved. Using the constant coefficient scaling method around the on-design point, acceptable results are achieved, but, for off-design points it gives unsatisfying results due to increasing magnitude of error. Knowing that a gas turbine compressor often operates within off-design points range, it is realized that a model with a wide range of acceptability is required. Hence, a two-stage approach is taken. The first is dimensionless modeling of gas turbine compressor using variable coefficient scaling in on and off design points, and then testing of the engine compressor within possible ranges at Sharif Gas Turbine Lab. Obtaining the test results, the modeling predictions are validated.