近空间高超声速气动力数据天地换算研究

该文针对高升阻比面对称飞行器近空间高超声速飞行环境,考虑马赫数效应、粘性干扰效应和真实气体效应等多种复杂气动效应对飞行器气动力数据的影响,采用CFD数值模拟技术和气动数据相关性理论分析方法,建立了基于地面风洞试验外推获取实际飞行状态下气动力数据的天地换算方法;并采用CFD技术对气动力数据天地换算的精确性进行了验证。

基于气动力数据集的气动偏差建模与辨识

针对飞行器采用离散数据进行气动力建模的辨识需求,发展了一种基于气动力数据集的气动偏差建模与辨识方法。该方法利用离散数据可高效描述气动力非线性变化的特点,采用依据极大似然准则的牛顿-拉夫逊法,将气动力数据集与真实气动力的偏差作为辨识对象,利用线性模型进行气动偏差建模与辨识,避免了传统多项式气动力模型在辨识非线性气动力时参数过多、不便对离散气动力数据修正等问题。通过仿真飞行试验,对比了飞行器受扰动激励后的辨识拟合弹道与飞行仿真弹道,并进行了全局攻角下的飞行器阻力系数、升力系数和俯仰力矩系数辨识修正结果和真实值的对比。结果表明:辨识拟合弹道与真实飞行弹道基本重合,辨识修正后的气动力与真实值吻合较好,所建立的方法是正确、有效的,具有良好的实用性。

非定常气动力建模研究与虚拟飞行试验验证

非定常气动力建模涉及空气动力学、飞行力学、飞行控制等多个领域,是完善飞机大迎角气动数据库的关键。传统的气动数据库模型为动导数模型,由静态气动力、旋转天平、动导数等数据构成,无法精细表征过失速机动状态下的非定常效应。循环神经网络(RNN)结构是一种处理和预测序列数据的神经网络结构,在人工智能领域运用广泛,与非定常气动力一样都具有时间序列依赖的特点。重点研究了循环神经网络在非定常气动力建模中的应用,利用单自由度俯仰振荡的风洞试验数据进行建模。使用强迫运动试验与虚拟飞行试验2种方法对非定常模型进行验证:在强迫运动试验中,通过直接对比气动力曲线,对具有实战意义的眼镜蛇机动进行了验证;在虚拟飞行试验中,通过对比试验与建模仿真的运动参数曲线,验证了气动力模型的准确性。2种验证方法均表明循环神经网络模型比传统动导数模型更接近试验结果。

基于循环神经网络的非定常气动力建模研究

随着超机动概念的提出和过失速机动的飞行实现,非定常气动力建模问题成为空气动力学、飞行力学、飞行控制领域共同关注的研究课题。传统的气动数据库由静态、动态数据和旋转天平数据构成,无法精细表征过失速机动状态下气动力的非定常效应。循环神经网络(RNN)结构是一种用于处理和预测序列数据的神经网络结构,在人工智能领域被广泛运用,与非定常气动力一样都具有时间序列依赖的特点。本文重点研究了循环神经网络在非定常气动力建模中的应用,利用单自由度俯仰振荡的风洞试验数据进行建模,对“眼镜蛇”机动动作的气动力进行预测,并与传统气动数据库以及风洞试验的结果进行对比,结果表明在复杂过失速机动的气动力预测上,包含非定常气动力的循环神经网络建模结果比传统气动力数据库更接近试验结果,对非定常气动力有着更好的表征。最后研究了如何向多自由度耦合进行扩展的问题。

基于神经网络的故障飞机仿真

传统气动系数模型中 ,拟合法精度较差 ,插值法计算速度慢 ,且占内存多。利用神经网络一致逼近任意非线性连续函数的特性 ,训练具有一个三输入六输出的神经网络模型 ,建立故障飞机仿真系统。仿真结果和故障飞机自修复应用表明 ,文中所采用的神经网络建模方法是可行的。在自修复飞行控制系统研究中 ,为故障飞机建模所需大量故障状态气动系数数据处理提供一种新思路。

Hardware-in-loop Simulation(HLS) of Homing Anti-tank Missile

The simulation techniques of hardware-in-loop simulation(HLS) of homing antitank missile based on the personal computer (PC) are discussed. The PC and MCS-96 chip controller employ A/D and D/A boards (with photoelectricity isolation) to transfer measur ment and control information about homing head, gyro and rudder and utilize the digital hand shaking board to build correct communication communication protocol. In order to satisfy the real-time requirement of HLS, this paper first simplifies the aerodynamic data file reasonably, then builds a PC software with C language. The program of the controller part is made with PL/M language. The simulation of HLS based on PC is done with the same sampling period of 10ms as that of YH-F1 and the experiment results are identical to those of digital simulation of the homing anti-tank guided missile.

Multi-SPline Technique for the Extraction of Drag Coeffidents from Radar Data

In the preparation of firing tables, the determination of projectile drag coefficientsthrough firing test radar data reduction is very important. Many methods have been developed for this work but none of them appear to be satisfactory in one Way or another. Inthis paper a multi-spline model of drag coefficient (cd) curve is developed that can guaranteefirst derivative continuity of the cd curve and has good flexibility of fitting accurately to acd curve from subsonic up to supersonic range. Practical firing data reduction tests showboth fast convergence and accurate fitting results. Typical velocity fitting RMS errors are0.05-0.08 m/s.

Kinetics of Photocatalytic Degradation of Gaseous Organic Compounds on Modified TiO_2/AC Composite Photocatalyst

This study is focused on the kinetic characteristics of photocatalytic degradation of gaseous organic compounds on modified titanium dioxide/activated carbon composite photocatalyst(MTA).The MTA,which co-doping with iron(Fe) and nitrogen(N),was synthesized by a sol-gel method,and its photocatalytic performance was investigated under different reaction conditions.The experimental data obtained were tested by the zero,first and second order kinetic model,and the factors affecting the kinetic model were analyzed.It was clearly demonstrated that the experimental data of toluene and acetone on MTA fit quite well with second order kinetic model equation,but the experimental data of formaldehyde fits well with zero order kinetic model equation.

Wavelet neural network aerodynamic modeling from flight data based on pso algorithm with information sharing and velocity disturbance

For the accurate description of aerodynamic characteristics for aircraft,a wavelet neural network (WNN) aerodynamic modeling method from flight data,based on improved particle swarm optimization (PSO) algorithm with information sharing strategy and velocity disturbance operator,is proposed.In improved PSO algorithm,an information sharing strategy is used to avoid the premature convergence as much as possible;the velocity disturbance operator is adopted to jump out of this position once falling into the premature convergence.Simulations on lateral and longitudinal aerodynamic modeling for ATTAS (advanced technologies testing aircraft system) indicate that the proposed method can achieve the accuracy improvement of an order of magnitude compared with SPSO-WNN,and can converge to a satisfactory precision by only 60 120 iterations in contrast to SPSO-WNN with 6 times precocities in 200 times repetitive experiments using Morlet and Mexican hat wavelet functions.Furthermore,it is proved that the proposed method is feasible and effective for aerodynamic modeling from flight data.

DIAGNOSIS OF WAVE ACTIVITY OVER RAINBAND OF LANDFALL TYPHOON

A generalized wave-activity density, which is defined as an absolute value of production of three-dimensional vorticity vector perturbation and gradient of general potential temperature perturbation, is introduced and its wave-activity law is derived in Cartesian coordinates. Constructed in an agoestrophic and nonhydrostatie dynamical framework, the generalized wave-activity law may be applicable to diagnose mesoscale weather systems leading to heavy rainfall. The generalized wave-activity density and wave-activity flux divergence were calculated with the objective analysis data to investigate the character of wave activity over heavy-rainfall regions. The primary dynamical processes responsible for disturbance associated with heavy rainfall were also analyzed. It was shown that the generalized wave-activity density was closely correlated to the observed 6-h accumulative rainfall. This indicated that the wave activity or disturbance was evident over the frontal and landfall-typhoon heavy-rainfall regions in middle and lower troposphere. For the landfall-typhoon rainband, the portion of generalized wave-activity flux divergence, denoting the interaction between the basic-state cyclonic circulation of landfall typhoon and mesoscale waves, was the primary dynamic process responsible for the evolution of generalized wave-activity density.

Prediction of Aircraft＇s Longitudinal Motion Based on Aerodynamic Coefficients and Derivatives by Surrogate Model Approach

The accuracy of a flight simulation is highly dependent on the quality of the aerodynamic database and prediction accuracies of the aerodynamic coefficients and derivatives. A surrogate model is an approximation method that is used to predict unknown functions based on the sampling data obtained by the design of experiments. This model can also be used to predict aerodynamic coefficients/derivatives using several measured points. The objective of this paper is to develop an efficient digital flight simulation by solving the equation of motion to predict the aerodynamics data using a surrogate model. Accordingly, there is a need to construct and investigate aerodynamic databases and compare the accuracy of the surrogate model with the exact solution, and hence solve the equation of motion for the flight simulation analysis. In this study, sample datas for models are acquired from the USAF Stability and Control DATCOM, and a database is constructed for two input variables （the angle of attack and Mach number）, along with two derivatives of the X-force axis and three derivatives for the Z-force axis and pitching moment. Furthermore, a comparison of the value predicted by the Kriging model and the exact solution shows that its flight analysis prediction ability makes it possible to use the surrogate model in future analyses.

Aerodynamic Performances of Wind Turbine Airfoils Using a Panel Method

One of the key features of Laplace＇s Equation is the property that allows the equation governing the flow field to be converted from a 3D problem throughout the field to a 2D problem for finding the potential on the surface. The solution is then found using this property by distributing ＂singularities＂ of unknown strength over discretized portions of the surface： panels. Hence the flow field solution is found by representing the surface by a number of panels, and solving a linear set of algebraic equations to determine the unknown strengths of the singularities. In this paper a Hess-Smith Panel Method is then used to examine the aerodynamics of NACA 4412 and NACA 23015 wind turbine airfoils. The lift coefficient and the pressure distribution are predicted and compared with experimental result for low Reynolds number. Results show a good agreement with experimental data.

An assessment of summer sensible heat flux on the Tibetan Plateau from eight data sets

The eight datasets of the summer (June-August) surface sensible heat (SH) flux over the Tibetan Plateau (TP) are compared on the time scales of the climatology,interannual variability and linear trend during 1980-2006.These data sets include five reanalyses (National Center for Environmental Prediction reanalysis,NCEPR1 and NCEPR2,NCEP climate forecast system reanalysis,CFSR,Japanese 25-year reanalysis,JRA,and European Centre for Medium Range Weather Forecasts reanalysis,ERA40),two land surface model outputs (Noah model data of Global Land Data Assimilation System version 2,G2_Noah,and Simple Biosphere version 2 output by Yang et al.,YSiB2),and estimated SH based on China Meteorological Administration (CMA) station observations,ObCh.The results suggest that the summer SH on the TP differs from one dataset to another due to different inputs and calculations.Climatologically,the ERA40 and JRA distribute rather uniformly while the other six products show similar regional disparities,that is,larger in the west than in the east and stronger in the north and the south than in the middle of the plateau.The mean magnitude of the SH averaged over the 76 stations above the TP varies considerably among each dataset with the difference of more than 20 W m?2 between the maximum (G2_Noah) and minimum (ObCh).Nevertheless,they are consistent in the interannual variability and mostly show a significant decreasing trend corresponding to the weakening surface wind speed,in spite of the distinct trend for the ground-air temperature difference among the different data sets.These two consistencies indicate the particular availability of the SH products,which is helpful to the relevant climate dynamics research.

Calibration of a γ-Re_θ transition model and its application in low-speed flows

The prediction of laminar-turbulent transition in boundary layer is very important for obtaining accurate aerodynamic characteristics with computational fluid dynamic(CFD)tools,because laminar-turbulent transition is directly related to complex flow phenomena in boundary layer and separated flow in space.Unfortunately,the transition effect isn’t included in today’s major CFD tools because of non-local calculations in transition modeling.In this paper,Menter’sγ-Re_θtransition model is calibrated and incorporated into a Reynolds-Averaged Navier-Stokes(RANS)code-Trisonic Platform(TRIP)developed in China Aerodynamic Research and Development Center(CARDC).Based on the experimental data of flat plate from the literature,the empirical correlations involved in the transition model are modified and calibrated numerically.Numerical simulation for low-speed flow of Trapezoidal Wing(Trap Wing)is performed and compared with the corresponding experimental data.It is indicated that theγ-Re_θtransition model can accurately predict the location of separation-induced transition and natural transition in the flow region with moderate pressure gradient.The transition model effectively imporves the simulation accuracy of the boundary layer and aerodynamic characteristics.

Design of Off-statistics Axial-flow Fans by Means of Vortex Law Optimization

Off-statistics input data sets are common in axial-flow fans design and may easily result in some violation of the requirements of a good aerodynamic blade design.In order to circumvent this problem,in the present paper,a solution to the radial equilibrium equation is found which minimizes the outlet kinetic energy and fulfills the aerodynamic constraints,thus ensuring that the resulting blade has acceptable aerodynamic performance.The presented method is based on the optimization of a three-parameters vortex law and of the meridional channel size.The aerodynamic quantities to be employed as constraints are individuated and their suitable ranges of variation are proposed.The method is validated by means of a design with critical input data values and CFD analysis.Then,by means of systematic computations with different input data sets,some correlations and charts are obtained which are analogous to classic correlations based on statistical investigations on existing machines.Such new correlations help size a fan of given characteristics as well as study the feasibility of a given design.