航空发动机反推作动器楔形缓冲结构研究

为了削弱航空发动机反推作动器在展开过程末端的强烈机械冲击,将楔形液压缸缓冲结构应用于该反推作动器。本文建立了该反推作动器节流缓冲的数学模型和Simulink仿真模型,对该作动器在缓冲过程中的速度特性和时间特性进行仿真,分析了速度和压力对其缓冲特性的影响。研究结果表明,本文提出的楔形缓冲结构有助于减小航空发动机反推作动器活塞与筒体的碰撞速度,能有效削弱工作末端的冲击;在保证运行速度不变的前提下,可以通过适当降低系统的通油压力来提高反推作动器的节流缓冲效果。

航空发动机反推作动器卡滞故障分析

反推作动器用于同步驱动反推力装置移动外罩展开,实现大型飞机在着陆后或中断起飞(RTO)过程中减小飞机速度、缩短滑跑距离,尤其是在雨雪天气下,保证飞机安全降落。针对某发动机反推作动器外场卡滞无法收起的故障问题,通过反推作动系统工作原理分析,开展了卡滞故障原因分析,建立了作动器卡滞故障树。然后对底事件逐一排查,对产品分解检查以及试验验证,最终确定该卡滞故障是由于反推作动器在侧向载荷作用下丝杠丝母传动副卡滞,进而导致反推力装置无法收回。最后,通过对丝母内螺纹牙尖增加倒角,并在模拟反推力装置侧向载荷的试验条件下开展改进产品试验验证。结果表明,丝母的内螺纹牙尖增加倒角后,减小了丝杠丝母传动副在侧向载荷下的摩擦力,减轻了磨损,提高了反推作动器在工作中承受侧向载荷的能力,防止作动器卡滞。本文故障分析方法与结果对外场同类故障排除具有积极的指导意义,也为后续同类产品改进设计和新研产品开发奠定了坚实的基础。

Stereoscopic PIV Measurements of the Flow Field in a Turbine Cascade

This paper presents experimental measurements of the flow field in a Low-speed Turbine Cascade using a stereoscopic particle-image velocimetry(SPIV). During the measurements, a pair of frame-straddling-based CCD cameras were configured at different sides of the laser light sheet, and appropriate tracing particles(DEHS) were employed. The measurements were conducted at the incidence angle of 0 degree and exit Reynolds number of 1.7 × 105 with the tip clearance 1.18% of blade chord. The tip flow features, such as the evolution and breakdown of tip leakage vortex, the horseshoe vortex, turbulence characteristics of tip leakage flow, were studied for the flow field analysis. The results showed that the tip leakage flow/vortex mainly dominate flow fields in the tip region. The tip leakage vortex performs as a concentrated vortex before its breaking down and splitting into small vortices. The highest turbulence intensity mainly occurs in the tip region along with the trajectory of tip leakage vortex, and when the vortex breaks down, the turbulence intensity reduces rapidly. Additionally, the SPIV with this configuration also shows an advantage in investigating the flow structures and mechanism inside the turbine cascade.

Experimental Investigation of Effects of Suction-Side Squealer Tip Geometry on the Flow Field in a Large-scale Axial Compressor using SPIV

It is well known that the non-uniform tip geometry is a promising passive flow control technique in turbomachinery.However,detailed investigation of its effects on the unsteady flow field of turbomachinery is rare in the existiug hteratures.This paper presents an experimental investigation of effects of suction side squealer tip configuration on both the steady and unsteady flow field of an isolated compressor rotor.The flow field at 10%chord downstream from the trailing edge was measured using a mini five-hole probe.Meanwhile,the unsteady flow field inside the passage was investigated using stereo particle image velocimetry(SPIV).The steady results show that the SSQ tip configuration exerts positive effect on the static pressure rise performance of this compressor,and the radial equilibrium at the rotor outlet is obviously rearranged.The SSQ tip configuration would create a stronger tip leakage vortex at the formation phase,and it experiences a faster dissipation process around the rear chord.Also,the splitting process of the tip leakage vortex is severer,which is the main cause of the relatively higher probability of the presence of the streamwise reverse flow.The quantitatively analysis of the tip leakage vortex indicates that the velocity loss inside the blockage region is direct response of the evolutionary procedure of the tip leakage vortex.It keeps increasing until the end of the splitting process.Although the blockage coefficient grows sustainably,the velocity loss will reduce once the turbulent mixing procedure is dominant.

Role of a Single Shield in Thermocouple Measurements in Hot Air Flow

To investigate the role of a single shield on steady temperature measurement using thermocouples in hot air flow,a methodology for solving convection, conduction, and radiation in one single model is provided. In order to compare with the experimental results, a cylindrical computational domain is established, which is the same size with the hot calibration wind-tunnel. In the computational domain, two kinds of thermocouples, the bare-bead and the single-shielded thermocouples, are simulated respectively. Surface temperature distribution and the temperature measurement bias of the two typical thermocouples are compared. The simulation results indicate that: 1)The existence of the shield reduces bead surface heat flux and changes the direction of wires inner heat conduction in a colder surrounding; 2) The existence of the shield reduces the temperature measurement bias both by improving bead surface temperature and by reducing surface temperature gradient; 3) The shield effectively reduces the effect of the ambient temperature on the temperature measurement bias; 4) The shield effectively reduces the influence of airflow velocity on the temperature measurement bias.