بررسي تاثير افزايش فشار كندانسور بر كارايي مراحل كم‌فشار توربين بخار، به‌كمك شبيه‌سازي عددي

Numerical Investigation of Two-phase Flow in Low-Pressure Stages of a Steam Turbine to Study Effects of Variations in Condenser Pressure

افزايش فشار كندانسور مستقيماً بر عملكرد توربين بخار تاثير خواهد داشت. براي بررسي اين تغييرات، مي‌توان از شبيه‌سازي عددي توربين بخار و تحليل رفتار آن، به‌عنوان يك راهكار كاربردي استفاده ‌كرد. در اين پژوهش تلاش شده تمامي هفت مرحله ناحيه‌ي كم‌فشار توربين بخار توسط نرم‌افزار ANSYS-CFX به‌صورت سه‌بعدي و پايا شبيه‌سازي و تحليل ‌شود. براي اطمينان از صحت نتايج، نتايج به دست آمده با نتايج حاصل از اندازه‌گيري‌هاي تجربي توربين بخار واقعي مقايسه، و نشان داده شد كه با نتايج تجربي به‌خوبي مطابقت دارد. در نهايت راندمان (يعني نسبت كار توليدي)، كيفيت بخار، خطوط جريان و پروفيل فشار براي پره هاي مراحل پاياني توربين در فشارهاي مختلف كندانسور محاسبه ‌شد تا اثر افزايش فشار كندانسور بررسي كمي و كيفي ‌شود. اين مقايسه نشان‌گر رفتار توربين بخار براساس تغييرات فشار كندانسور، و نيز تاثير‌گذاري آن بر توربين است.

Modern steam turbines are used routinely in various power plant electricity productions. In order to obtain descriptions of the complete flow-field of the LP stages of a steam turbine, numerical simulation of a steam turbine is performed. In steam power plants, increasing condenser pressure leads to a complex three-dimensional two-phase flow. Any jump in the back pressure of the turbine outlet results in lower steam axial velocity at LP stages. Consequently, a stall region is formed in the last rotational blade of the LP stages, which causes unstable vibrations known as stall flutter. Numerical simulations are more robust in detailed examination of different phenomena in steam turbines, since experimental examination of the flow field is relatively expensive. In this study, the flow field of the whole LP region of a steam turbine (7 stages) is simulated with steady 3D computational fluid dynamics (ANSYS CFX). The flow path is defined by the ANSYS-Blade editor, and the computational 3D structured grid was generated by ANSYS-Turbo Gird software. In addition, all boundary conditions and initial conditions applied in this study are explained. The flow rate, pressure, temperature and mass friction on the blades are computed via CFD simulation, and overall, good agreement with the experimental data is observed. The efficiency, available work, streamline and pressure distribution of the LP region are reported for analysis of the turbine performance change, due to pressure, of the steam turbine outlet (Condenser Pressure) variations. Since any jump in the pressure of the turbine outlet results in lower steam axial velocity in the LP stages, the turbine performance deviates from its design point. In this study, a stall region, the alarm and critical pressure of a turbine outlet were calculated.