基于磁滞电机的无人机舵回路设计CSCD

舵回路是无人机飞行控制系统中的一个重要环节。飞行控制系统通过舵回路控制无人机的角运动,从而实现对无人机的操纵使其稳定飞行。基于某型号磁滞电机和"田口"三次设计方法,分析了位置反馈和速度反馈对舵回路的影响,确定了其取值范围,设计了某型号无人机舵回路,并进行了仿真试验,试验结果表明,该设计是可行的。     

边界层抽吸和脉动反压作用下隔离段内流动特性研究

为了解上游边界层抽吸控制和下游周期脉动反压作用下隔离段内流动特性,采用非定常数值模拟和理论分析相结合的方法,对来流Ma=2情况下的隔离段内激波串动态演化特性、激波串形态结构变化以及激波串演化迟滞现象进行了研究。结果表明,在脉动反压和边界层抽吸作用下,激波串在上游抽吸狭缝与下游隔离段出口之间周期振荡,振荡频率与脉动反压一致。在振荡过程中,首道激波串形态在规则反射与马赫反射以及马赫反射与弧形激波(包含正激波)之间相互转换。边界层抽吸将激波串固定在抽吸狭缝位置,有效提高了隔离段抗反压性能,脉动频率越大,可承受的瞬态反压峰值越大。在一个振荡周期内,激波串向上移动速度较向下移动更快,且在上下移动过程中形态变化存在迟滞现象。     

同轴喷嘴自发激励高频燃烧不稳定性试验研究

为增进对液氧煤油火箭发动机同轴离心喷嘴燃烧不稳定性过程的理解,在大气环境下进行了同轴离心喷嘴的自发激励燃烧不稳定性试验。试验采用单喷嘴敞口模拟燃烧室,高温的氧气和空气混合物从同轴喷嘴的直流喷嘴喷注,高温的煤油蒸气从同轴喷嘴的离心喷嘴喷注。通过逐步改变氧化剂流量使模拟燃烧室内产生自发激励高频燃烧不稳定性,使用脉动压力传感器和黑白高速相机记录稳定和不稳定燃烧工况下的脉动压力和火焰。研究发现：气气同轴离心喷嘴的自发激励高频燃烧不稳定过程呈现“滞后”现象;不稳定工况下的火焰均为脱口火焰,火焰特征长度约等于喷嘴出口到脱口火焰团上沿的距离;气气同轴离心喷嘴燃烧不稳定性的发生原因可以被认为是因混合特征时间与声学特征时间相关。     

Wake structure and similar behavior of wake profiles downstream of a plunging airfoil

Very limited attention has already been paid to the velocity behavior in the wake region in unsteady aerodynamic problems.A series of tests has been performed on a flapping airfoil in a subsonic wind tunnel to study the wake structure for different sets of mean angle of attack,plunging amplitude and reduced frequency.In this study,the velocity profiles in the wake for various oscillation parameters have been measured using a wide shoulder rake,especially designed for the present experiments.The airfoil under consideration was a critical section of a 660 kW wind turbine.The results show that for a flapping airfoil the wake structure can be of drag producing type,thrust producing or neutral,depending on the mean angle of attack,oscillation amplitude and reduced frequency.In a thrust producing wake,a high-momentum high-velocity jet flow is formed in the core region of the wake instead of the conventional low-momentum flow.As a result,the drag force normally experienced by the body due to the momentum deficit would be replaced by a thrust force.According to the results,the momentum loss in the wake decreases as the reduced frequency increases.The thrust producing wake pattern for the flapping airfoil has been observed for suffi ciently low angles of attack in the absence of the viscous effects.This phenomenon has also been observed for either high oscillation amplitudes or high reduced frequencies.According to the results,for different reduced frequencies and plunging amplitudes,such that the product of them be a constant,the velocity profiles exhibit similar behavior and coalesce on each other.This simi larity parameter works excellently at small angles of attack.However,at near stall boundaries,the similarity is not as evident as before.     

Hysteresis behaviors of compressor rotating stall with cusp catastrophic model

Rotating stall is a complex nonlinear dynamic phenomenon which is always characterized by catastrophe and hysteresis in high aerodynamic-loading compressor. Exploring the key contributing factors and characteristic rules of hysteresis is very important for compressor design and flow instability control. In this paper, a novel model method is proposed to analyze the hysteresis behaviors to extend the understanding of compressor rotating stall. The equilibrium states of compressor system under different conditions are first described based on Moore-Greitzer model. Then, through assessing the stability of the equilibrium points by Liapunov's theorem, the ratio of shutoff head to compressor characteristic semi-height is found to affect the stall hysteresis: the size of hysteresis loop will gradually decrease, even disappear with the increase of the ratio. Combing the effects of both the ratio and throttle coefficient, the hysteresis behaviors of compressor stall under multi-parameters can be found to be consistent with the topological properties of cusp catastrophic model by Thom’s catastrophe theory. Finally, according to topological invariant rules, from the perspective of potential function, the equilibrium surface equation of compressor system is developed by standard cusp catastrophic model to describe the various hysteresis behaviors of compressor rotating stall along different control routes.     

Flow response hysteresis of throat regulation process of a two-dimensional mixed-compression supersonic inlet

The variable geometry supersonic inlet tends to decrease the throat area to reduce the Mach number upstream of the terminal shock, so as to reduce the flow loss. However, excessive Internal Contraction Ratio(ICR) exposes the inlet to a greater risk of unstart, which inevitably results in a process of increasing the throat area to aid the inlet restart. In the above throat regulation process, the inlet undergoes the start, unstart, and restart states in turn. In order to reveal the flow structure...     

微秒脉冲等离子体流动控制延迟效应研究

等离子体流动控制(PFC)能有效抑制翼型附面层分离,增加升力,推迟失速,应用前景广阔。流场的延迟效应是指采用PFC进行流动控制时,激励关闭后,流动控制效果仍存在的现象。本文对新型微秒脉冲介质阻挡放电(μs-DBD)的体积力和冲击波特性进行测试,并在此基础上开展风洞实验,进行流场的延迟效应研究,测试μs-DBD的延迟时间和参数影响规律。结果表明,μs-DBD能同时产生体积力和冲击波作用,同时也能在流场中产生明显的延迟效应,延迟时间不小于1200s,远大于毫秒脉冲介质阻挡放电(AC-DBD)产生的延迟时间(150s);激励电压和来流速度越大,翼型迎角越小,延迟效应越强;等离子体激励能使流场失稳分岔,并转变为更优的分岔解;延迟效应研究在节约能耗、延长激励器寿命、PFC控制律设计和风洞实验方法优化等方面有重要意义。     

Hysteresis and the nonlinear equivalent piezoelectric coeffcient of MFCs for actuation

The hysteretic behavior and nonlinearity of the equivalent material coefficient of macro fiber composites (MFC) under staircase input conditions are investigated using the Preisach model. Based on a database of first order reversal curves, formulas are derived to predict the hysteresis of strain output and nonlinearity of the equivalent piezoelectric coefficient of MFCs. Formulae are verified by comparing the predicted strains with the measured strains of three MFC specimens, which are driven by a random sequence of staircase voltage inputs. The coefficients obtained by the formulae and experimentation coincide. Further results indicate that the equivalent piezoelectric strain coefficient depends greatly on the value of drive voltage across the entire input range, and the coefficient is asymmetric across the negative and positive input ranges. Deflection testing of an MFC composite cantilever demonstrates the importance of taking the nonlinearity of the equivalent piezoelectric coefficient into consideration in the application of actuation.     

Experimental investigation of shock-buffet criteria on a pitching airfoil

An experimental investigation of the shock-buffet phenomenon subject to unsteady pitching supercritical airfoil around its quarter chord has been conducted in a transonic wind tunnel. The model was equipped with pressure taps connected to the fast response pressuretransducers. Measurements were conducted at different free-stream Mach number from 0.61 to0.76. The principle goal of this investigation was to experimentally discuss the shock-buffet criterion over a SC(2)-0410 supercritical pitching ...     

Oblique shock train motion based on schlieren image processing

In this paper, shock train motion in a Mach number 2.7 duct is studied experimentally, and large numbers of schlieren images are obtained by a high-speed camera. An image processing method based on Maximum Correlation Detection (MCD) is proposed to detect shock train motion from the schlieren images, based on which the key structures, e.g., separation positions and separation shock angles on the top and bottom walls, can be analysed in detail. The oscillations of the shock train are generated by rhombus and ellipse shafts at various excitation frequencies. According to the analysis of MCD results, the distributions of the frequency components of shock train oscillation generated by the two shafts are distinctly different, in which the motion generated by the ellipse shaft is much smoother; shock train motion is mainly characterized by the oscillation of separation position while the separation shock strength is not so sensitive to downstream disturbance; there is a hysteresis loop relation between the downstream pressure and separation position.