Investigation On The Effect Of Blade Tip Shaping On Performance And Aerodynamic Noise

Research has shown that appropriate shape of rotor blade tip is of great importance to the axial fan performance.Taking a two-stage variable-pitch axial fan as an example,Fluent is used to simulate the performance of the fan under five different blade tip shapes,and the internal dynamics,pressure distribution and loss characteristics are analyzed in the present paper so as to determine an excellent blade tip.Simulation results show that the five different blade tip shapes can improve the fan performance.Then the effects of blade tip grooving in a single stage or both stages on fan performance are compared,and the internal dynamics and the leakage losses are examined.Results show that the countercurrent-flow-grooved blade tip has the highest improvement in performance,followed by the double grooved blade tip,the up-step blade tip and the down-step blade tip.While the current-flow-grooved blade tip only improves fan performance in lower flow rates.After improving blade tip shapes,the internal dynamics tends to be more complex,and enhances the domain of the leakage vortex and vorticity intensity,resulting in the appreciable reductions of the axial velocity and the leakage flow in the tip clearance.The promotion of the countercurrent-flow-grooved blade tip is indicated by the increments of total pressure rise and efficiency of 4.68% and 0.94%,at the design flow rate.Considering the current requirements of ultra-low emission renovation in coal-fired power plants,the blade tip with countercurrent-flow-groove is the best choice for the axial flow fan.Besides,both blade tip grooving in different stages can improve the fan performance;the overall promotion of fan performance illustrates that the best scheme is the blade tip grooving in the first stage followed by the blade tip grooving in both stages and in the second stage,respectively.Although the scheme of the tip grooving in both stages enhances the full pressure rise most effectively,the domain of high efficiency is shrunk.After blade tip grooving,the internal dynamics in blade tip tends to be more complex,the static pressure reduces notably in the suction side and the tip leakage loss is declined distinctly.Considering the requirements of varying-load operation,the ultra-low emission innovation and tip grooving cost,the blade tip grooving in the first stage is a preferred scheme in practice.Then taking the flow field of different blade tip shapes converging in steady conditions as the initial flow field,the large eddy simulation and FW-H noise model is applied to obtain the distribution of sound source and the acoustic characteristics.The results show that after improving blade tip shapes,the noise level of the blade tip region and leading edge of blade argument apparently,which are the main sound sources.The blade tip shape has a significant effect on the amplitude of sound pressure,especially in close to the noise source.The noise in the fan is mainly aggregated at low and medium frequency,and the noise in all regions reach the peak value at the fundamental frequency.The effect of blade tip grooving on the sound level is exhibited as a small raise,and the morphology of the frequency spectrum is changed appreciably.