Research On Drags Of Coaxial Hub High Speed Helicopter

Although rigid coaxial rotor helicopter has broken through the forward flight speed limit of single rotor helicopter,the hub will generate a huge drag.Combining the methods of the numerical simulation and experimental study,the paper has done some research on the coaxial dual-hub drags and flow mechanisms of coaxial rotor helicopter.The main work is as follows:Firstly,the paper summarized recent research situation of the hub drag at home and abroad in rigid coaxial rotor helicopter,and pointed out the urgent problem which should be solved in the study.Based on the CFD method,a set of calculation model was established in the second chapter,which is suitable for large flow field separation.Then,the model was proved to be effective for the single helicopter fuselage example.O n this basis,the author calculated the hub drag of the typical coaxial dual-rotor helicopter in this chapter,analyzed the main reasons of the hub drag,and explored the corresponding measures to reduce the hub drag.Adopting the calculation method mentioned in the second chapter,the third chapter focused on CFD calculation for each component of the hub,then analyzed the drag and flow field characteristic of different shape s of hub fairing,intermediate shaft fairing and pylon.According to the conclusion from the third chapter,six kinds of fairing models were combined and numerical calculation was carried out to different fairing combination models in the fourth chapter.Meanwhile,the chapter analyzed the rule of drag characteristics to high-speed coaxial dual-rotor helicopter hub combination models,which included major axis hub fairing,intermediate shaft fairing and pylon with different length.And the rule provided reference for the following experiment study.The result shows that in order to reduce hub drag,it should reduce or eliminate flow separation in the rear of intermediate shaft rather than simply change hub fairing shape.At last,a coaxial dual-hub model test rig is designed in the fifth chapter.Based on this test rig,a set of wind tunnel tests were conducted by balance force measurement and oil-flow visualization for different coaxial dual-hub combination models to verify and supplement the calculation results.It is shown by the test results that the drag of coaxial dual-hub test models affected by symmetric smooth hub rotation can be ignored,but the gaps between the fairing components have a great influence on the models' drag,and the big gap will cause the drag increase.The separated wake after every fairing component produces strong aerodynamic interaction between each other,and makes the drag increased obviously.More than that,this paper proves that the drag of hub can be reduced by lengthening intermediate shaft fairing and pylon.