This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are rela...This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are related to the flow angle and mainstream parameters;then by adopting the classic flow topology of behind-blade wakes,the effect of operating conditions is included in the plot and a model for flow angle is thus developed.The advantage of the model is that it can achieve off-design flow angle estimations with design flow characteristics and it is compatible with CFD-based throughflow methods.This model is then implemented into a standard CFD-based throughflow solver from the previous research to estimate off-design characteristics of blade rows with proper input-output strategies.Furthermore,the effect of loss upon flow angle is also modeled as corrections to the proposed model.The model is validated on a compressor stage and the results show promising accuracy for off-design flow angle estimations.展开更多
The effect of the wake of previous strokes on the aerodynamic forces of a flapping model insect wing is studied using the method of computational fluid dynamics. The wake effect is isolated by comparing the forces and...The effect of the wake of previous strokes on the aerodynamic forces of a flapping model insect wing is studied using the method of computational fluid dynamics. The wake effect is isolated by comparing the forces and flows of the starting stroke （when the wake has not developed） with those of a later stroke （when the wake has developed）. The following has been shown. （1） The wake effect may increase or decrease the lift and drag at the beginning of a half-stroke （downstroke or upstroke）, depending on the wing kinematics at stroke reversal. The reason for this is that at the beginning of the half-stroke, the wing “impinges” on the spanwise vorticity generated by the wing during stroke reversal and the distribution of the vorticity is sensitive to the wing kinematics at stroke reversal. （2） The wake effect decreases the lift and increases the drag in the rest part of the half-stroke. This is because the wing moves in a downwash field induced by previous half-stroke＇s starting vortex, tip vortices and attached leading edge vortex （these vortices form a downwash producing vortex ring）. （3） The wake effect decreases the mean lift by 6%-18% （depending on wing kinematics at stroke reversal） and slightly increases the mean drag. Therefore, it is detrimental to the aerodynamic performance of the flapping wing.展开更多
基金funded through the National Science and Technology Major Project(2017-Ⅲ-0009-0035)National Natural Science Foundation of China(Grant No.52276031)。
文摘This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are related to the flow angle and mainstream parameters;then by adopting the classic flow topology of behind-blade wakes,the effect of operating conditions is included in the plot and a model for flow angle is thus developed.The advantage of the model is that it can achieve off-design flow angle estimations with design flow characteristics and it is compatible with CFD-based throughflow methods.This model is then implemented into a standard CFD-based throughflow solver from the previous research to estimate off-design characteristics of blade rows with proper input-output strategies.Furthermore,the effect of loss upon flow angle is also modeled as corrections to the proposed model.The model is validated on a compressor stage and the results show promising accuracy for off-design flow angle estimations.
基金The project supported by the National Natural Science Foundation of China(10232010)the National Aeronautic Science Fund of China(03A51049)
文摘The effect of the wake of previous strokes on the aerodynamic forces of a flapping model insect wing is studied using the method of computational fluid dynamics. The wake effect is isolated by comparing the forces and flows of the starting stroke （when the wake has not developed） with those of a later stroke （when the wake has developed）. The following has been shown. （1） The wake effect may increase or decrease the lift and drag at the beginning of a half-stroke （downstroke or upstroke）, depending on the wing kinematics at stroke reversal. The reason for this is that at the beginning of the half-stroke, the wing “impinges” on the spanwise vorticity generated by the wing during stroke reversal and the distribution of the vorticity is sensitive to the wing kinematics at stroke reversal. （2） The wake effect decreases the lift and increases the drag in the rest part of the half-stroke. This is because the wing moves in a downwash field induced by previous half-stroke＇s starting vortex, tip vortices and attached leading edge vortex （these vortices form a downwash producing vortex ring）. （3） The wake effect decreases the mean lift by 6%-18% （depending on wing kinematics at stroke reversal） and slightly increases the mean drag. Therefore, it is detrimental to the aerodynamic performance of the flapping wing.
