Flow Field Characteristics Research And Design Optimization For A High Efficiency Counter-Rotating Fan

The designs, flow fields characteristics, performance optimizations and experimental measurements on a conunter-rotating axial flow fan and an air cannon are studied by using a methodology of combining experiment and simulation. The experiments are conducted respectively in the axial fan test rig and air cannon test rig in Institute of Engineering Thermophysics, Chinese Academy of Sciences. The numerical simulations are conducted by the three-dimensional viscous software NUMECA. The thesis is composed of two parts as follows:The major part of this dissertation is the research on design, flow field investigation and experiment of the counter-rotating axial flow fan. The proper load ratio of two rotors for the counter-rotating fan is firstly deduced by a theoretical analysis. Numerical simulation of the cascades is carried out to investigate flow characteristics for replacing experiment. Using the three-dimensional optimization model for cascade performance optimum is tested, which shows the method can be used for searching better cascade. The optimized cascade used in the rotor has less flow loss with more uniform pressure profile and much less velocity gradient in wake region. The analysis demonstrates cascade loss depends on the attack angle in the low speed flow, hereby, the effect of cascade profile optimization is limited for improving cascade performance.The tip clearance research shows that tip loss plays an important role in the overall loss of the fan. With increasing the tip clearance, the mass flow and total pressure decreases. Efficiency of the counter-rotating fan decreases more than normal axial flow fans with the same tip clearance. The tip leakage vortex develops from the blade leading edge and the distances from the vortex core to up end-wall and suction side both change generally linearly, with the mix loss region expanding. The rear rotor tip leakage vortex is more intense and influence region is bigger than that of the forward rotor. The forward rotor tip leakage vortex weakens in the rear rotor flow passage. The tip clearance influence should be considered to control the tip loss during the design procedure.Finally, a methodology of combining the S2 design program and three-dimensional flow field analysis is implemented to design the counter-rotating fan. The total performances of the stage and the fan are remarkably improved. The optimized fan has a high efficiency in the large operation range and achieves the design requirement. The fan runs steadily in the range of 70～130% designed mass flow. The total pressure efficiency is higher than 80% over the range of 70～116% designed mass flow and the total efficiency is as high as 86% at the designed flow rate. The rear rotor motor runs smoothly over the whole operating flow rate. The detailed flow field characteristics and loss mechanism is studied by numerical simulations. It is found that the key point to improve the fan performance is to control the hub region loss, especially for the rear rotor, which can be achieved by optimizing the spanwise circulation distribution of two rotors load and using meridian acceleration hub.The appendix reports the theoretical analysis, numerical simulation and experiment results of the air cannon. The theoretical analysis shows that the main factors in determining the air cannon performance are the exhaust nozzle diameter, the piston sleeve inlet and the Laval nozzle. The optimized geometry parameters of the air cannon are obtained by using numerical simulations. And the following experimental measurements indicate that the computations well predicts the steady and unsteady performance of the air cannon. The impulse force of the optimized model is 50% higher than that of the original KL50 air cannon under the tested conditions. For the cases with working pressure of 0.8MPa, the optimized design is 66% higher than the original one.