Study On Aerodynamic Characteristics Of Stratospheric Aerostat And Propeller

There are some problems with the aerodynamic design of stratospheric aerostat.First of all,the drag of the hull accounts for about 2/3 of the whole body.It is necessary to extract the parameters that are most sensitive to the drag coefficient of the hull to achieve the purpose of reducing the optimization design dimension,and forming the design space of the airship by these parameters.Secondly,the non-conformal aerostat has time-varying shape during the round trip which causes the normal contraction or expansion speed of the envelope,which will form a coupling speed with the incoming flow.Accurate modeling of the dynamics of non-conformal aerostat must take into account the time-varying aerodynamic effects.Finally,the slippery effect caused by the propeller will affect the hull,meanwhile,the flow field of the hull will affect the performance of the propeller.The mutual interference increases the complexity of the aerodynamic characteristics of the airship-propeller system.In view of the above problems,we systematically studied the shape parameter sensitivity of the airship,the dynamic time-varying shape drag characteristics of the superpressure balloon and the bidirectional aerodynamic interference between airship and propeller.The main work contents and conclusions are as follows:(1)The shape of the hull was described by the PARSEC airfoil parameterization method,and the sensitivity of each parameter was determined and ordered by Sobol's global sensitivity analysis method.The results show that the hull head radius r_h and the maximum cross-sectional radius r_d of the hull have the highest sensitivity to the total drag coefficient.The design space can be composed of r_h and r_d,which are in the interval[0,0.06]and[0.08,0.12],respectively.(2)The update of the aerostat contour grid nodes were implemented by piecewise cubic Hermite interpolation and diffusion smoothing method.The effects of different expansion or contraction speeds and incoming flow speeds on the aerodynamic characteristics of non-conformal aerostats were analyzed.The results show that during the descending process,envelope shrinkage is beneficial to drag reduction,and the greater of shrinkage speed,and the better effect of drag reduction;during the ascending process,the envelope expansion is unfavorable for drag reduction,the greater of expansion speed,and the worse effect of drag reduction.The differential pressure drag is the main factor that causes the change of the total drag;the higher of wind speed,and the lower coupling effect caused by the contraction or expansion speed of the envelope.(3)The CFD method was used to study the aerodynamic characteristics of hull,propeller and mutual aerodynamic interference between them in detail.For the streamlined hull,when the propeller is arranged at the tail of the hull,the differential pressure will increase due to the suction effect.The results show that,for a three-stage hull,the propeller placed at the rear of the hull can reduce the differential pressure of the hull.The propeller at the maximum cross-sectional of the hull(for streamlined hull)or the middle of the cylindrical section(for three-stage hull)provides maximum pure thrust,however,the propeller efficiency is the lowest here.Arranging the propeller at the rear allows for the highest efficiency and lowest input power.