Application of an optical pressure measurement technique with pressure-sensitive paint to blow-down supersonic wind tunnel testing

压敏涂料作为一种新型的光学压力测量技术，以极高的空间分辨率获得全场压力分布，受到了广泛的关注。然而，传统的聚合物基PSPs由于对快速压力变化的响应缓慢而不能用于短持续时间的吹风型超音速风洞。本研究的目的是通过提高脉冲脉冲本身的时间响应和激励灯的稳定性，建立适用于下吹超音速风洞气动试验的脉冲脉冲测量技术。本文的主要研究成果如下：1.研究结果表明：蓝色发光二极管（LED）阵列光源输出波动极小（小于0.2%），适合于短持续时间2型吹风风洞中PSP测量的照明光源。基于多孔薄层色谱板的PSPs的时间常数约为10微秒。将快速响应的多孔PSP应用于富山县立大学下吹风洞拉瓦尔喷管的表面压力测量，成功地显示了喷管壁面斜激波系统产生的压力跳变以及激波位置的时间波动。下入过程中管壁温度的变化严重影响压力测量。使用导热胶带将多孔PSP固定在黄铜壁上（作为散热片），可以有效降低实验过程中表面温度的变化。由于不可避免的散点噪声，得到的单幅图像的信噪比不够。结果表明，在短持续时间风洞中进行PSP测量时，图像降噪处理是非常重要的。

Pressure-sensitive paint (PSP) attracts attention as a novel optical pressure measurement technique to obtain the full-field pressure distribution with very high spatial resolutions. However, conventional polymer-based PSPs cannot be used in short-duration supersonic wind tunnels of blow-down type due to the slow response to a rapid change in pressure. The aim of the present study is to establish PSP measurement technique applicable to aerodynamic tests in blow-down supersonic wind tunnels by improving the time response of PSP itself and the stability of excitation lights. The main results of the present work are as follows:1. The fluctuation of the output of a blue light-emitting diode (LED) array light source is extremely small (less than 0.2%), hence it is suitable for the illumination light for the PSP measurements in short-duration wind tunnels of blow-down type.2. The time constants of PSPs based on porous thin-layer chromatography plates are on the order of 10 microseconds. The fast-responding porous PSP has been applied to a surface pressure measurement in a Laval nozzle of the blow-down wind tunnel of Toyama Prefectural University, and pressure jumps due to a system of oblique shock waves generated in the nozzle wall and temporal fluctuations of the shock locations have been successfully visualized.3. The wall temperature change during a run seriously affects the pressure measurements. The use of a thermally-conductive adhesive tape to fix the porous PSP on a brass wall (as a heat sink) was effective to reduce the surface temperature change during the experiment.4. The signal-to-noise ratio (SNR) of a single image obtained is not enough due to the inevitable shot noise. It suggests that the image processing procedure for the noise reduction is important for PSP measurements in short-duration wind tunnels.