Mitsuru Kurita

Practical pressure-sensitive paint measurement system for industrial wind tunnels at JAXA

Japan Aerospace Exploration Agency (JAXA) has constructed the JAXA practical pressure-sensitive paint (PSP) measurement system for their large industrial wind tunnels. Its system and application tests were introduced. Contents of the system which included PSP paint, pressure calculation method and apparatus were described. A high accuracy pressure calculation method, a priori/in situ hybrid method, was also introduced and applied to the data processing. For validating this PSP system, an experiment using an ONERA M5 standard model was conducted in a transonic wind tunnel. PSP results represented global quantitative pressure distribution. The PSP data accuracy, 2σ, of the system compared with pressure taps was 1.9 kPa (Cp = 0.06 at M = 0.84). Then, the JAXA practical PSP measurement system was applied to the Japanese regional jet development test. Its results also represented a detailed and global flow structure on the test model. 2σ of PSP data was Cp = 0.06 at cruising condition. It was proved that the present PSP system could be applied to practical tests at a large industrial transonic wind tunnel.

Temperature Correction of Pressure-Sensitive Paint for Industrial Wind Tunnel Testing

Pressure-sensitive paint measurement can obtain a much more detailed surface pressure distribution than can be obtained using conventional pressure taps. However, the pressure-sensitive paint is sensitive not only to pressure but also to temperature, and where high accuracy is required, it is essential to compensate for this temperature dependency. This paper discusses data processing methods for pressure-sensitive paint measurement in transonic industrial wind tunnel testing, and proposes three methods to compensate for temperature dependency of the pressure-sensitive paint: an in situ method, an a priori method, and a hybrid of a priori and in situ methods. The pressure distributions from the pressure-sensitive paint data obtained by these proposed methods are compared with pressure tap data measured by conventional pressure transducers, and it is confirmed that the proposed methods are effective in compensating the temperature dependency of pressure-sensitive paint and improve the accuracy of the obtained data. It is also found that the hybrid of a priori and in situ methods is widely applicable to the industrial wind tunnel testing even if the pressure range of the pressure tap data is limited.

Data Processing of Pressure-Sensitive Paint for Industrial Wind Tunnel Testing

Data processing methods for pressure-sensitive paint measurement in industrial wind tunnels are discussed in this paper. Key tasks are to shorten the processing time and to improve the accuracy of data. To complete data processing within a limited time frame, it has to be performed as continuously and automatically as possible. The methods to promote automation of the data processing are discussed. Solving an issue of temperaturedependency of pressure-sensitive paint is indispensable for enhancing accuracy of data. Two approaches to compensate for the temperature-dependency, i.e. a-priori method and temperature-corrected in-situ method, are applied in this study. As the result, processing time has been shortened by solving problems preventing automation of image registration process. The PSP data processed by both a-priori method and temperature-corrected in- situ method showed reasonable agreement with the pressure tap data measured by pressure transducers, indicating the validity and accuracy of the present data processing methods.

Development of Bi-Luminophore Pressure-Sensitive Paint Systems

Bi-luminophore pressure-sensitive paint (bi-PSP) has been developed in order to correct the error due to temperature dependence of PSP and increase PSP measurement accuracy. The bi-PSP was composed of pressure-and temperature-sensitive dye. Tetranuclear europium (III) complexes and PdTFPP were used as temperature-and pressure-sensitive dye, respectively. The luminescence intensity of the Eu complex was highly sensitive to temperature and insensitive to pressure. The bi-PSP was examined using a painted coupon and its characteristics were clarified. As a verification test, pressure distributions on a supersonic transport (SST) model at low-speed flow were acquired by the bi-PSP measurement system. The root mean square of Cp at 50m/s was approximately 0.1 (150 Pa) at flow speed of 50m/s, indicating that this bi-PSP system can measure more accurately pressure than conventional pressure conversion technique using reference PSP images immediately after stop of wind tunnel free stream. Furthermore, pressure images at angles of side-slip were clearly visualized, although PSP/temperature-sensitive paint (TSP) combined system can not acquire the overall pressure images of the whole model surface.

In-Flight Wing Deformation Measurement

This study has been conducting research on in-flight measurement for deformation of main wing of an aircraft. In this paper, a measurement method which optically measures the deformation of the main wing using high-resolution cameras is discussed. It also discusses a measurement system and a camera calibration. The measurement technique was applied to JAXA’s experimental aircraft, a twin-propeller plane with sweepback angle of zero degree, and it demonstrates to measure the quantitative changes of bending and twist angle of the main wing in flight.

Multi-Camera Pressure-Sensitive Paint Measurement

A multi-camera system leads a dramatic improvement to productivity of a pressuresensitive paint measurement in an industrial wind tunnel because the system measures pressure distribution of nearly whole of a test model at a time. However, in the multi-camera pressure-sensitive paint measurement system, there is a technical challenge to enhance the measurement accuracy of data that include overlapping areas observed by more than one camera. The problems to discuss are differences on seams at switching of cameras, the selfillumination correction, the pressure transformation method using individual calibration data of each camera and the temperature dependency of the pressure sensitive paint. This paper proposes a data processing method for the multi-camera pressure sensitive paint measurement, and it presents results of wind tunnel tests at transonic speeds to evaluate the proposed method.

Aerodynamic Characteristics of a Lifting-Body-Type Reentry Vehicle at Transonic Speeds

A flowfield investigation of a lifting-body-type reentry vehicle at transonic speed by pressure-sensitive paint measurement has been conducted. The purpose of this study is to investigate two different flowfields for baseline and upswept upper-aft body configurations of the vehicle by detailed surface pressure measurement, which nonlinear lift characteristics around angle of attack of 5 deg at transonic speeds were found for the baseline configuration while the configuration with upswept upper-aft body had nearly linear lift characteristics in the former researches. As a result, it is found that the nonlinear lift characteristic of the baseline configuration is caused by a qualitative change of flow pattern on the upper-aft body near fin and inboard surface of the fin, where the expansion wave generates the lift at the angle of attack 0 deg while the flow in the same region loses the lift at the angles of attack 5 − 15 deg due to the boundary layer separation. On the other hand, unlike the baseline configuration, it is observed for the configuration with upswept upper-aft body that the flowfield on the same region shows no flow pattern change with the change of angle of attack, leading to the nearly linear lift characteristics.

Effects of wall temperature on skin-friction measurements by oil-film interferometry

Wind-tunnel skin-friction measurements with thin-oil-film interferometry have been taken on an aluminum sample to investigate the effects of wall temperature on the accuracy of the technique. The sample has been flush-mounted onto a flat plate with an electric heater at its bottom and mirror-smooth temperature-sensitive paint sprayed on its top. The heater has varied the sample temperature from ambient to 328 K, and the paint has permitted wall temperature measurements on the same area of the skin-friction measurements and during the same test. The measured wall temperatures have been used to calculate the correct oil viscosities, and these viscosities and the constant nominal viscosity at 298 K have been used to calculate two different sets of skin-friction coefficients. These sets have been compared to each other and with theoretical values. This comparison shows that the effects of wall temperature on the accuracy of skin-friction measurements are sensible, and more so as wall temperature differs from 298 K. Nonetheless, they are effectively neutralized by the use of wall temperature measurements in combination with the correct oil viscosity–temperature law. In this regard, the special temperature-sensitive paint developed for this study shows advantages with respect to more traditional wall temperature measurement techniques.

Temperature Correction of PSP Measurement Using Bi-luminophore Dyes

Bi-luminophore Pressure-Sensitive Paint (bi-PSP) has been studied in order to correct the error due to temperature dependence of PSP and increase PSP measurement accuracy. The bi-PSP measurement systems including the paint, optical system and image processing tool, were developed in JAXA/ARD/WINTEC. The system was applied to the JAXA 2m x 2m transonic wind tunnel (TWT1) for evaluating its performance. The 90% down-scale F6 model (DLR civil-transport-type model) was used for the validation test. The bi-PSP system allowed us to correct the temperature error of the PSP and acquire simultaneously pressure and temperature images on the model. Furthermore, the whole pressure- and temperature- images of the F6 model was clearly visualized by using the multi-camera bi-PSP systems allocated on the walls of TWT1 test section.

Automatic Data Processing of Pressure-Sensitive Paint Measurement in a Wind Tunnel

In the industrial wind tunnel, the productivity is important as well as the accuracy of data. This paper describes a method to detect target markers in the image registration in order to automate data processing in a pressure-sensitive paint measurement. A technical challenge is how to detect target markers automatically without false detection. The feature of the proposed method is that it uses 3-dimensional information of the test model attitude in order to restrict the commingling of noise by predicting the position of the target marker and limiting the scope of searches. The proposed method is evaluated in JAXA’s 2m  2m transonic wind tunnel. As the result, it indicates that the proposed method is effective to detect target markers. And the proposed method leads high productive pressure-sensitive paint measurement to the industrial wind tunnel.