Aerodynamic analysis of a highly loaded compressor in semi‐closed cycles using a throughflow method

Abstract

This paper outlines the aerodynamic performance of a highly loaded 5‐stage compressor in a conceptual semi‐closed cycle. An in‐house throughflow computation procedure that has been proven to be a powerful tool in aerodynamic analysis for modern compressors is applied to simulate the compressor. The influences of changes in physical properties of the working medium with varying ratios of exhaust CO2 recirculation are considered in the computation. A series of numerical simulations is conducted with two settings depending on whether the rotational speed is set to obey the criterion of similarity. For the identical non‐dimensional speed parameter, the compressor can operate stably with pure CO2 as the working fluid. The distributions of aerodynamic parameters undergo no big differences under various CO2 contents; however, a somewhat little higher loss is observed for the 5th stage. When the absolute rotational speed is set according to the originally designed value, the compressor can bear a 25% CO2 content at the cost of a substantially narrowed working range, and a recirculation ratio of approximately 10% is a safe threshold value. The aerodynamic configuration also undergoes a notable redistribution given these circumstances; the load of the front stages is reduced, but the rear stages become the risk factors at near stall condition. This research reveals that from the compressor design point of view, a semi‐closed cycle is feasible using existing technology and that compressor modifications are needed according to situational requirements. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Numerical optimization of a highly loaded compressor in semi-closed cycles using neural networks and genetic algorithms

“…as a function of Π m . Unlike the results under design speed condition, as the flow range from chocking to stall is much larger, the whole speed lines remain nearly unchanged during the increase in CO 2 content. The change in choking flow rates is less than 0.5% at both speeds, while the value is 0.8% for the design speed.…”

“…To further validate the optimization results, a streamline curvature throughflow computation code which has been proven credible and powerful in previous studies is employed to simulate the optimized 5‐stage compressor. Because the first two rows of rotors are faced with a deteriorative flow status that becomes the main concern at part‐speed conditions, it can be inferred that the re‐staggered blades alter the inlet flow condition of the rotors, thus reducing the losses.…”

“…As the compressor performances in the semi‐closed cycle at the design speed have been investigated in previous research, the study here will focus on the part‐speed conditions. Two sets of numerical simulations are conducted, and the only difference between them is the rotational speeds which are 62% and 75% design‐speed, respectively.…”

“…The principal idea behind the current effort is the proposal of a fast, reliable and robust optimization framework that can search for the optimal solution for the variable vanes settings of multi‐stage compressors in semi‐closed cycles. The investigation is conducted on a newly developed 5‐stage highly loaded axial flow compressor whose aerodynamic performances under various CO 2 contents at design speed has been analyzed in the authors' previous research, and the test rig of the gas turbine which includes the compressor is planned to be modified to become a semi‐closed cycle. As the flow solver applied in this paper is an in‐house code that cannot be made public, an artificial neural network is incorporated into the optimization system acting as a surrogate model for the purpose of the universality of the newly developed optimization method.…”

Convective cooling model for aero-thermal coupled through-flow method

“…The through-flow method has been widely applied in the aerodynamic design of gas turbines since Wu 1 first developed the general theory in 1952. Since then, progress has been made to improve the through-flow method by Novak, 2 Denton, 3 and Li et al 4 With the cooling technology applied to cooled turbines, Mildner and Gallus, 5 Gehring and Riess, 6 and Petrovic and Wiedermann 7 also studied the cooling effect on different cooled turbines. Nevertheless, previous studies did the through-flow calculation and heat transfer calculation separately, without considering the aero-thermal coupled phenomenon.…”