Study On The Effect Of Riblet Structure On Airfoil Flow And Noise Characteristics

Drag reduction by riblet surface, as one of the bionic drag reduction technologies, is well known for its low power consumption and obvious drag reduction effect, and it is a practical and effective drag reduction method. Currently, the technology has been widely used in the marine, transportation, aerospace, fluid machinery, oil and gas transport, sports, medical and other fields.In this paper, the effect of riblet depth ratio on flow resistance in different speeds on three-dimensional channel is studied. In this part, the effect of riblet structure on local pressure is analyzed and then the basic flow parameters such as boundary layer velocity distribution, velocity gradient distribution, wall shear distribution, friction coefficient are analyzed. Ultimately, the drag reduction effect of different conditions are getted. In order to explain the effect of drag reduction, the effect of riblet structure on normal velocity fluctuation and longitudinal vortex are analyzed. The mechanism of drag reduction are analyzed from the perspective of vortex structures. The results showed that vortex formed in the groove can effectively reduce the velocity gradient and wall shear stress, eventually reduce the frictional resistance. The maximum drag reduction was 9.71% at the condition of β=90°. In the area where the riblet structure is arranged, the longitudinal vortex head upward angle becomes larger, so that ejection and sweep incident caused by the longitudinal vortex weakened and the frictional resistance effectively reduced. In addition, the longitudinal vortex unstable broken obviously in the riblet structure section. The spatial density distribution of the vortex flow is significantly reduced after flowing through the riblet structure section, this may be because riblet structure affects the self-sustaining process in the range of 20-60, and it can reduce wall friction.After getting the riblet structure drag reduction mechanism, the effects of the ridge structure layout position and pressure gradient on NACA0018 airfoil flow and noise characteristics were studied. The effects of riblet structure on boundary layer velocity distribution of airfoil, wake velocity distribution, surface pressure coefficient and lift to drag ratio were mainly analyzed. The effect of riblet structure to control energy dissipation was studied by analyzing the entropy generation. Finally, the monitoring point of the noise signal in the time domain and frequency were analyzed and the effects of noise characteristics of riblet structure on NACA0018 airfoil was studied. The results showed that riblet-H structure airfoil can effectively reduce the airfoil boundary layer separation area, reduce the wake velocity deficit, in addition can also increase the lift coefficient of the airfoil, airfoil reduce the drag coefficient at α=6°. At the conditions of velocity is 24m/s, the airfoil lift-drag ratio of riblet-H model improving the 53.418% compared with it in terms of smooth airfoil. In terms of noise, riblet-H airfoil model effectively reduces the noise in the 0-3000 Hz frequency range. Through the vortex structure and entropy generation analysis found that riblet-H airfoil can effectively control energy production and high entropy production structure of the vortex structure of dissipation at 6° angle of attack.