对转升力风扇地面效应的力学及喷流频谱特性研究

Experimental Study of In-Ground-Effect on Force and Spectrum Characteristics of a Contra-Rotating Lift Fan

关键词:  升力风扇  地面效应  对转  功率谱密度  实验研究

Key words:  Lifting fan  Ground effect  Contra-rotating  PSD (Power spectral density)  Experimental study

摘要:

为进一步了解升力风扇工作特性，以自行设计的20kg推力对转升力风扇为研究对象，设计和发展了对转涵道风扇测控系统，研究不同转速条件、不同离地距离(1.1D，2D，3D，D为转子直径)对升力风扇各部件力学特性的影响效应，结合动态压力传感器阵列测量技术及功率谱密度分析方法，获得了升力风扇的喷流频谱特性。结果表明:相比于3.0D工况，在设计转速下当离地高度降低到1.1D时，升力风扇总推力提高11%但需求功率基本不变，其中涵道唇口推力下降3%，转子推力上升25%，出现了明显的“气垫效应”；上、下游转子叶片尾迹能量较小，未能监测到明显的叶片通过频率，风扇喷流动态特性与前后级转子间动-动非定常干涉效应有明显相关性，其一阶频率为上、下游转子通过频率之和。

Abstract:

In order to further study the working characteristics of lift fan， present study conducted an experimental investigation on the in-ground-effect aerodynamic characteristics of a contra-rotating lift fan in terms of force generation and pressure spectrum. An experimental system including the control and measurement system is designed， in which the aerodynamic properties are revealed with different RPM and the distance of fan exit to ground(1.1D， 2D， 3D where D is the diameter of the lift fan). The spectrum characteristics of the exit jet flow have been investigated by means of high-response dynamic pressure sensors. Results revealed that the ‘air cushion’ effect occurred when the ground distance approaches to 1.1D. Compared with the 3.0D condition， the total thrust of lift fan increases by 11% but the demand power is almost the same when the ground distance of the lift fan is lowered to 1.1D， lift generated by the ducted lip was reduced by 3% while the lift from the contra-rotating rotors increased by 25% at the design speed. However， the power consumption did not show a noticeable variation at different ground distance. The dynamic pressure spectrum showed that a new signal dominate the characteristics of the jet flow due to the strong interaction between the contra-rotating rotor rows. The first order frequency is identical to the sum of the blades for both rotor rows. Besides， the fluctuation of the wake from the rotors cannot be observed clearly.