航空发动机喘振引起转子系统横向载荷的确定方法

对喘振引起的转子系统的横向载荷进行了研究,对发动机喘振过程中的压力脉动信号进行FFT分析和相关分析,识别出旋转失速时失速团的旋转速度,推断出整个截面的压力分布,进而得到了喘振对转子的横向作用力。     

Binary integration of fluctuating targets

The detection performance of a binary integrator (M-out-of-N detector) against nonfluctuating, slowly fluctuating, and quickly fluctuating targets is given. Since the solution for the slowly fluctuating target is numerically intensive, a simpler approximate solution is developed. This approximation is very accurate and is valid even when the noise power varies from pulse to pulse within a single antenna scan     

再人飞行器脉动压力环境的分析与预测

本文分析了机动再入飞行器因非定常空气动力流动引起的物面脉动压力环境,并根据高超声速无粘流计算的表面压力分布,给出了一套预测各种脉动压力环境统计特性的工程计算公式。算例表明,预测的均方根脉动压力、功率谱密度和交叉功率谱密度与实验值是一致的。     

底部流动脉动压强特性研究

利用脉动压力测量技术，研究细长旋成体底部流动百定常特性，实验Ｍ数０．６－３．５。实验中对不同的体构型模型进行测量，通过对测得的功率谱密度曲线，脉劝压强均方根值以及相关函数等结果的分析比较，探讨底部流动非定常特性的某些规律以及模型外形等因素的影响。     

Fluctuating Target Detection in Clutter Using Sidelobe Blanking Logic

In an earlier paper, Maisel [6] considered two-channel detection systems using a sidelobe blanking logic when a nonfluctuating target was present. This paper is an extension of the earlier work to include fluctuating targets. The Swerling I, II, III, and IV models are considered when single-pulse detection is of interest. An adaptive threshold procedure is also briefly discussed whereby the probability of false alarm at any given resolution cell is maintained constant, even though the input clutter level may vary from cell to cell or from beam position to beam position. Useful data are presented for detection probabilities in the range 0.5 to 0.9, for false alarm probabilities in the range 104 to 10-8, and for a false detection probability of 0.1 for a sidelobe target yielding an apparent signal to total noise power density ratio of 13.0 dB in the main beam receiver.     

Mean-Level Detection Utilizing a Digital First-Order Recursive Filter

The use of a simple digital first-order recursive filter for mean-level detection is described. Performance characteristics are derived for the case where the background noise is stationary, and detection results are given for Swerling Case 2 fluctuating signals. Equations are derived for computing false-alarm performance in nonstationary backgrounds, and results are given for some special cases. Comparisons are made with performance of a conventional mean-level circuit in stationary and nonstationary noise.     

脉动压力相关时最大瞬时畸变值的预估

给出了脉动压力相关时最大瞬时畸变值的估算式;与实验值比较表明,考虑脉动压力相关可明显提高最大瞬时畸变值的估算精度。考虑脉动压力相关后,不同条件下参数(K_(max)-K_(ss))估算的平均误差可由19.96％降至11.84％;参数(K-K_(ss))和σ_K估算的平均误差也分别由28.16％和11.37％降至12.33％和5.43％。此外还讨论了脉动压力相关程度对最大瞬时畸变预估值的影响。当平均相关系数(?)≤0.1时,不同条件下估算值相对误差均小于3％,这时可不考虑脉动压力相关。     

Detection Results for Scanning Radars Employing Feedback Integration

A method is presented for the calculation of the detection probabilities for a scanning radar employing feedback integration. An equation is developed for the optimum feedbacd value? the equation holds for small and large sample sizes and for fluctuating and nonfluctuating targets. Then, a value for the antenna beam-shape factor is given which enables one to calculate detection probabilities.     

What was learned from the new VFE-2 experiments

In the present paper the main results of the new experiments from VFE-2 are summarized. These include some force and moment results, surface and off-body measurements, as well as steady and fluctuating quantities. Some critical remarks are added, and an outlook for future investigations is given.     

涡喷发动机对湍流型动态压力畸变频率响应的实验研究

 一、研究与分析方法 本实验在地面台架上的一台涡喷发动机上进行。图1为试验装置前段及挡板装置简图。挡板用以产生较强的湍流型动态压力畸变,而压气机出口测点的动态压力P₂*与进口环面相应半径上测点的动态压力P₁*则构成相关分析的输出与输入信号。动态压力测量采用Kulite微型固态压阻式传感器,并经放大系统,由磁带机记录下在湍流型动态压力畸变工况时发动机进入漂移型喘振的压力信号过程,试验后通过磁带机回放压力脉动数据,并在信号分析仪上处理。为了得到准确的喘前压力脉动数据,直接以喘振发生时的P₂*激烈下降作为同步外触发信号,并采用负向时间延迟来控制喘前数据采集,从而保证了喘前信号的可靠性。     

Detection of chi-square fluctuating targets in arbitrary clutter

In a recent paper, general expressions were derived for the density and cumulative probability functions of the amplitude of a linear matched-filter output given a nonfluctuating target in a clutter-limited environment. These expressions were based on the clutter amplitude density function. The results are extended to calculate the cumulative probability function of the output of a linear matched filter used to detect a chi-square fluctuating target in a clutter-limited environment. The resulting method is applied to a common radar clutter model, and experimental sonar data.     

Mean-Level Detection of Nonfluctuating Signals

Analysis of the performance of a mean-level threshold in the detection of nonfluctuating signals is performed. Formulas for the probability of detection are derived and a simple recursive method that can be used for computations is described. Binary integration is discussed, and it is shown that the loss in sensitivity due to the use of an adaptive threshold followed by binary integration is only a fraction of a decibel when compared with optimum binary integration. Binary integration results are given for both fluctuating and nonfluctuating signals.     

Direct Evaluation of Radar Detection Probabilities

A simple and effective procedure for evaluating detectionperformances in radar and sonar detection problems is derived forboth fixed-threshold and adaptive-threshold detection. Using theprocedure, the cumulative probabilities of the test statistic can bedirectly evaluated from the moment generating functions bycalculating residues. The exact formulae for computing the detectionperformances for the chi-square family of fluctuating targets withan integer fluctuation parameter are given in a finite sum formwithout any special functions for both fixed threshold and cellaverageconstant false-alarm rate detection by using the methoddeveloped here.     

Detection of Target Multiplicity Using Monopulse Quadrature Angle

The feasibility of using the indicated quadrature angle of arrival of a monopulse radar to discriminate a single target from multiple targets, separated in angle within a radar resolution cell, is investigated. The analysis is performed for steady (fixed) and Rayleigh fluctuating targets which cover a broad range of target characteristics. In both cases, the interfering signals due to noise and clutter in the sum and difference monopulse channels are assumed to be independent, zero-mean Gaussian processes. Detection and false alarm probabilities are evaluated analytically and the receiver operating characteristics are obtained for both fixed and fluctuating target cases. It is shown that multiple targets can be discriminated from a single target condition by integrating the indicated monopulse quadrature angle of arrival from several independent pulses. It is also shown that the probability of detecting multiple targets increases as the fluctuation in the target radar cross section decreases, approaching the fixed amplitude case in the limit.     

轴流压缩机粘性尾迹噪声研究

本文研究了微弯机翼在正弦阵风作用下的脉动升力,并导出计算公式,分析了动、静叶栅几何及气动参数对转子脉动升力及噪声级的影响。     

战斗机垂尾脉动压力数值模拟

在亚跨超计算流体力学（CFD）软件平台（TRIP）上开发了基于RANS/LES混合思路的IDDES流动模拟技术,并通过NACA0021翼型60°大迎角分离流动与串列圆柱绕流模拟对RANS/LES混合方法的精确度进行了验证,针对某战斗机外形的垂尾脉动压力开展了数值模拟研究。战斗机来流马赫数为0.1,基于全机长度的雷诺数为2×10⁶,模型迎角为20°、30°和40°。分别通过脉动压力系数、脉动压力功率谱密度、空间流动结构以及侧向力响应曲线等对战斗机的垂尾脉动压力进行了分析。脉动压力模拟结果表明：当垂尾完全沉浸在边条翼脱体涡破碎后的宽频湍流脉动气流中时,垂尾翼梢位置的脉动压力会发生明显的增大。     

Some Aspects of Swerling Models for Fluctuating Radar Cross Section

The structure of Swerling's 1957 model for fluctuating radar cross section and signal amplitude is examined prinwrily in terms of mixture representations. The authors also show the relationship of Nakagami's m distrubution to Swerling's amplitude distribution, and Nakagami's q distribution (Hoyt vector density) is reduced to the Swerling distribution. Nonuniform phase distributions associated with Swerling's functions are also derived. Results are given when Swerling's amplitude density is used as a prior distribution with Bennett's (Rice's) distribution for the amplitude of a sine wave plus narrowband Gaussian noise.     

动态射流控制附面层的分离

本文介绍了利用动态涡流器的流向涡和垂直于型面振动的射流所产生的横向涡的联合作用来控制大攻角下翼型表面附面层分离的实验。实验结果表明 :两种涡的作用能有效地同时推迟附面层分离和提前其再附着 ,使分离区大大缩小 ,附面层内的速度分布相应变得极为饱满。     

A methodology for simulating 2D shock-induced dynamic stall at flight test-based fluctuating freestream

A comprehensive methodology for simulating 2 D dynamic stall at fluctuating freestream is proposed in this paper.2 D CFD simulation of a SC1095 airfoil exposed to a fluctuating freestream of Mach number 0.537 ± 0.205 and Reynolds number 6.1 × 10~6(based on the mean Mach number) and undergoing a 10° ± 10° pitch oscillation with a frequency of 4.25 Hz was conducted.These conditions were selected to be representative of the flow experienced by a helicopter rotor airfoil section in a real-life fast forward flight.Both constant freestream dynamic stall as well as fluctuating freestream dynamic stall simulations were conducted and compared.The methodology was carefully validated with experimental data for both transonic flow and dynamic stall under fluctuating freestream.Overall, the results suggest that the fluctuating freestream alters the dynamic stall mechanism documented for constant freestream in a major way, emphasizing that inclusion of this effect in the prediction of dynamic stall related rotor loads is imperative for rotor performance analysis and blades design.     

几种矩形二维柱体节段模型上脉动力的测量

本文运用一种气动力直接测量方法在风洞的平滑流中测量了几种不同高宽比的二维矩形柱体上的脉动力，给出了它们的脉动升力系数的均方根值及斯特洛哈数，测量到在高宽比为０．７的柱体上有旋涡脱落诱发的顺风向脉动力。当风速变化时，顺风向脉动力的主导频率等于脉动升力频率或为其倍频。