Study On Aerodynamic Characteristics And Evaluation Methods Of Ground Vortex Under Headwind Conditions

With the increase of the diameter of the large bypass ratio turbofan engine,the problem of the ground vortex of the intake becomes more and more serious and cannot be eliminated.When the ground vortex is sucked into the intake,the total pressure loss in the intake will be caused,which will cause the compressor blades to vibrate.As the debris inhaled by the ground vortex can damage the compressor and the turbine blades,it has a serious impact on the engine.In this paper,the short-storied intake model is taken as the research object,and meshing is carried out.The influence of different influencing factors on the ground vortex structure and its aerodynamic characteristics under headwind conditions is obtained by numerical calculation.First,the reliability of numerical calculation is verified by comparing the experimental data with foreign countries and the simulation results of this paper.Secondly,under the headwind condition,the influence of the inflow velocity and the ground clearance on the aerodynamic characteristics of the ground vortex is considered.The results show that the aerodynamic characteristics of the ground vortex increase first and then decrease with the increase of the forward flow velocity,and the rotation direction of the ground vortex changes.When the direction of rotation changes,a step phenomenon occurs in the aerodynamic characteristic curve of the ground vortex.As the ground clearance increases,the ground vortex intensity and total pressure distortion decrease at the same far forward flow velocity.The aerodynamic characteristics of the ground vortex under different ground clearances first increase and then decrease,but the peak of the aerodynamic characteristic curve will appear hysteresis.After that,the influence of the velocity gradient on the aerodynamic characteristics of the ground vortex is considered.The results show that the ground vortex formed by the near-surface section under the velocity gradient in the Y direction is a pair of vortices with opposite directions of rotation.The larger the velocity gradient,the greater the ground vortex intensity and the total pressure distortion index,and the hysteresis will appear at the peak.In the Z-direction velocity gradient,the ground vortex formed by the near-surface section is a single vortex structure,and a vortex body is formed above the inlet passage.The ground vortex intensity and total pressure distortion index will increase first and then decrease,and the peak will not appear hysteresis.Finally,the aerodynamic characteristics of the engine ground vortex are evaluated from the aspects of ground vortex strength,total pressure distortion and swirl distortion.The results show that as the intake angle increases,the ground vortex intensity and total pressure distortion index will increase.The swirl formed by the inlet of the inlet gradually transitions from a pair of counter-rotating vortices to a single vortex.When the intake angle reaches90°,it becomes a pure crosswind condition,and a small swirl flow is formed on the wall surface of the intake passage due to the influence of the wall surface layer.The overall vortex index gradually increases,and the vortex index decreases,and the swirling flow changes from a typical vortex structure to a partial eddy current structure.This paper also uses SC₆₀,CC₆₀,C₆₀ to evaluate the swirling distortion,and points out that the evaluation indicators used with different working conditions should also change accordingly.When the intake angle is from 0°to 50°,the C₆₀ and CC₆₀0 are used to comprehensively evaluate the swirl distortion.When the intake angle is from 50°to 90°,the SC₆₀ can be used to evaluate the swirl distortion.The above research can provide a corresponding reference for the future evaluation of the ground vortex.