Development And Application Of Unsteady Pressure Measurement Technique Based On Fast-responding Pressure-sensitive Paint

Fast-responding pressure-sensitive paint(fast PSP)is an optical-based global pressure measurement technique in aerodynamic experiments.It can make up for the shortcomings of traditional pressure transducers,such as low spatial resolution,limited location,etc.,and realize the full field pressure measurement at a relatively low cost.More importantly,this technique can also solve the challenges in application on rotating parts and realize the unsteady pressure measurements on fast rotating blades.With the development of aerodynamics and increasing demands for aerocraft performance,advanced testing technology and accurate full field pressure test results play a more and more important role in improving both understandings for the complex flow mechanism and aerodynamic design level for advanced aerocrafts.Therefore,in order to improve the aerospace technology in China,it is of great significance to develop the measurement technique based on fast-responding pressure-sensitive paint and corresponding measurement system.Meanwhile,helicopter is a special type of aerocraft and the flow filed around a helicopter roter is extremely complex.To study this flow field,advanced measurement technique is especially required.Thus,the research goal of this paper is to develop the measurement methods based on fast PSP,and establish a complete set of measurement system for the unsteady pressure measurement.This measurement system is then applied to helicopter flow field.Pressure distributions on a fixed model in rotor flow filed and on fast rotating blades are successfully measured.Firstly,fabrication procedure of fast PSP is introduced.Then,static calibration system is established,which is then used to obtain the pressure and temperature sensivity of the fast PSP.In order to study the dynamic response of fast PSP,dynamic calibration systems based on resonance tube and shock tube are established separately.The shock tube system is then used to study the step response of fast PSP.Based on the different coating parameters including paint thickness,surface roughness and light attenuation,a mathematical model describing the dynamic response mechanism of pressure-sensitive paint is established.Based on this model,the coating structure is optimized and a step response within 50 microseconds is achieved.When PSP is applied to the pressure measurements on fixed models,the main challenge is the limited pressure resolution.To solve this problem,a high-precision measurement system for unsteady pressure fluctuation using intensity-based method is established in this paper.Also,a comprehensive noise reduction method based on proper orthogonal decomposition and phase average method is developed.By applying the developed method,a 10 times higher measurement accuracy is achieved and the pressure fluctuation within 50 Pa is successfully captured.Then,this method is used to study the interaction between the tip vortex and a cylinder in the real rotor flow field.The unsteady pressure measurement on the cylinder surface is achieved with high temporal and spatial resolution.The results show that the tip vortex can cause complex pressure fluctuations on the cylinder surface.For the plane obstacles,the tip vortex will induce two adjacent low and high pressure regions on the model surface,while the wedge-shaped obstacles will cut off the tip vortex and generate two low pressure regions on both sides of the wedge.According to the results,pressure fluctuation level in the high-pressure area is generally smaller than the low-pressure area.Therefore,it can be concluded that the plane windward structure has a better effect for suppressing the vibration and noise source.When PSP is applied to the pressure measurements on fast rotating blades,the main challenge is the significant temperature-indeced error.To solve this problem,a pressure measurement system for fast rotating blades using single-shot lifetime-based method is established.Also,a pressure and temperature joint measurement system is established and a correction method based on two-dimensional temperature distribution is developed,which can significantly improve the measurement accuracy.Then,the effect of this method is validated on a 2m diameter rotor test bench at China Aerodynamics Research and Development Center.Compared with the former temperature correction method,the proposed method successfully reduces the measurement error by an amount of 14-27%.Finally,the surface pressure distributions on a BO-105 rotor blade in hover and forward flight conditions are measured and the influence of a series of parameters including rotor collective pitch,thrust coefficient and advance ratio is analyzed.The findings provide important information for improving helicopter aerodynamic design.