轴流风机的进口径向畸变研究

对轴流风机的进口速度畸变情况进行了分析,利用改进的双激盘理论通过进口速度分布的改变来分析进口畸变对于性能的影响,并且将模型的计算结果与实际的实验结果相比较,得到一种合理的速度分布.      

机床定位精度对磁流变抛光的影响分析

根据KDMRF-1000磁流变抛光机床的结构形式,建立机床坐标系.对机床进行运动求解,得到磁流变抛光机床后置处理算法模型.在此模型的基础上,分析了机床各轴定位精度对磁流变抛光加工的影响,进行仿真分析,得到了误差的影响规律和对机床的定位精度要求.     

RBFs-MSA Hybrid Method for Mesh Deformation

Simulating unsteady flow phenomena involving moving boundaries is a challenging task,one key requirement of which is a reliable and fast algorithm to deform the computational mesh.Radial basis functions(RBFs) interpolation is a very simple and robust method to deform the mesh.However,the number of operations and the requirement of memory storage will be increased rapidly as the number of grid nodes increases,which limits the application of RBFs to three-dimensional(3D) moving mesh.Moving submesh approach(MSA) is an efficient method,but its robustness depends on the method used to deform the background mesh.A hybrid method which combines the benefits of MSA and RBFs interpolation,which is called RBFs-MSA,has been presented.This hybrid method is proved to be robust and efficient via several numerical examples.From the aspect of the quality of deforming meshes,this hybrid method is comparable with the RBFs interpolation;from the aspect of computing efficiency,one test case shows that RBFs-MSA is about two orders of magnitude faster than RBFs interpolation.For these benefits of RBFs-MSA,the new method is suitable for unsteady flow simulation which refers to boundaries movement.     

某粉末冶金高温合金涡轮盘破裂转速分析

介绍了平均应力法、平均径向应力修正法、残余变形法、局部塑性应变法等破裂转速预测方法,并采用这些方法对某粉末冶金高温合金涡轮盘破裂转速进行了分析.通过理论预测与试验结果的对比得知:采用平均径向应力修正法、残余变形法、局部塑性应变法预测的破裂转速与试验结果吻合较好,而采用基于径向应力分布均匀假设的平均应力法推算的破裂转速与试验结果相差较大.      

基于径向基神经网络的气动热预测代理模型

为快速获取高超声速飞行器表面热流数据并缩短飞行器气动热设计周期,提出了一种基于径向基神经网络的气动热快速预测代理模型方法。首先,在飞行器表面每一个离散化的网格节点单独构造一种正则化的径向基神经网络。随后,通过训练集对所有网络同时进行训练,获得各自网络的连接权值。最后,所有网格节点的神经网络协同预测飞行器表面不同位置的热流。对NASA火星实验室的椭圆钝化高超声速飞行器的应用表明,所提出的代理模型方法在模型训练完成后能够快速进行飞行器表面热流预测,并且模型具有良好的泛化能力,在驻点及迎风大面积区域热流预测结果与数值模拟的偏差在10%以内。     

基于分层思路的动态非线性气动力建模方法

很多非线性气动力模型难以精确预测系统的小扰动线性特征。针对这一局限,提出了一种非线性分层模型,用于辨识跨声速非线性非定常气动力。分层建模需要同时提供微幅振荡和大幅振荡两套训练样本,首先通过线性模型(如带外输入的自回归(ARX)模型)对微幅振荡样本进行建模,而后采用非线性模型(如径向基函数神经网络(RBFNN))对大幅振荡的样本与线性模型的差量进行建模,进而把线性模型和非线性模型的输出相叠加,得到分层非线性动力学模型。算例表明建立的分层气动力模型与单一自回归径向基函数(AR-RBF)神经网络模型相比不仅具有更高的数值精度,可以精确预测大幅运动中的非线性特征,而且在小扰动状态下自动退化为线性模型,能够精确刻画结构微幅振荡下的线性动力学特性。     

Reduced order model for unsteady aerodynamic performance of compressor cascade based on recursive RBF

Based on Recursive Radial Basis Function (RRBF) neural network, the Reduced Order Model (ROM) of compressor cascade was established to meet the urgent demand of highly efficient prediction of unsteady aerodynamics performance of turbomachinery. One novel ROM called ASA-RRBF model based on Adaptive Simulated Annealing (ASA) algorithm was developed to enhance the generalization ability of the unsteady ROM. The ROM was verified by predicting the unsteady aerodynamics performance of a highly-loaded compressor cascade. The results show that the RRBF model has higher accuracy in identification of the dimensionless total pressure and dimensionless static pressure of compressor cascade under nonlinear and unsteady conditions, and the model behaves higher stability and computational efficiency. However, for the strong nonlinear characteristics of aerodynamic parameters, the RRBF model presents lower accuracy. Additionally, the RRBF model predicts with a large error in the identification of aerodynamic parameters under linear and unsteady conditions. For ASA-RRBF, by introducing a small-amplitude and high-frequency sinusoidal signal as validation sample, the width of the basis function of the RRBF model is optimized to improve the generalization ability of the ROM under linear unsteady conditions. Besides, this model improves the predicting accuracy of dimensionless static pressure which has strong nonlinear characteristics. The ASA-RRBF model has higher prediction accuracy than RRBF model without significantly increasing the total time consumption. This novel model can predict the linear hysteresis of dimensionless static pressure happened in the harmonic condition, but it cannot accurately predict the beat frequency of dimensionless total pressure.     

轮盘径向破裂转速计算方法分析及修正

分析了轮盘径向破裂转速理论计算方法及常用平均径向应力计算方法的含义及其特点.且依据理论计算方法的含义,提出了基于有限元计算结果的轮盘径向破裂转速计算修正方法.通过实例应用,证明了相对于理论方法计算结果,修正方法较常用平均径向应力方法计算精度更高,其计算精度由6.6%提高到0.5%以内,且修正方法较理论方法使用更方便、工程适用性更强.      

小型共轴式直升机旋翼桨叶铰链力矩研究

从工程实际出发,建立了共轴双旋翼直升机桨叶铰链力矩计算模型.引入Leishman-Beddoes指数函数的半经验公式,建立了二维翼型非定常气动模型;引入干扰因子到Pitt-Peters动态入流模型,建立了反映共轴双旋翼直升机上下旋翼气动干扰的诱导速度模型;从桨叶的挥舞动力学模型出发,利用四阶Runge-Kutta算法求解桨叶刚性挥舞角的数值解,并利用模态叠加法计算桨叶的挥舞向变形.最后,通过对在研共轴直升机的计算得知,上下旋翼桨叶铰链力矩虽然在分量上有所差异,但是总的铰链力矩基本相同;中高速飞行时,上下旋翼桨叶铰链力矩在下倾斜盘累积成为使下倾斜盘前倾的力矩.