American Institute of Aeronautics and Astronautics

PSP Measurement of a High-Lift-Device Model in JAXA 6.5m×5.5m Low-Speed Wind Tunnel

Kazunori Mitsuo*, Mitsuru Kurita†, Shigeru Kuchi-Ishi‡, Keisuke Fujii§, Takeshi Ito** and Shigeya Watanabe§§ Institute of Aerospace Technology, Japan Aerospace Exploration Agency, TOKYO, 182-8522, JAPAN

and

Kazuomi Yamamoto†† Aviation Program Group, Japan Aerospace Exploration Agency

Pressure-Sensitive Paint (PSP) measurement system was developed in JAXA 6.5m x 5.5m low-speed wind tunnel. PSP painting and optical system for large-scale low-speed wind tunnel were constructed. Pressure images on a high-lift-device (HLD) model, which was built for R&D for next generation of civil transport aircraft, were measured. The dependence of pressure patterns on flow speed and angle of attack was investigated. Pressure map peculiar to the HLD model was clearly visualized. The measurement accuracy of the present low-speed PSP system was approximately 0.16 - 0.2 in Cp at 60m/s. The PSP system allowed us to acquire pressure images at the flow-speed of over 30 m/s.

I. Introduction ressure-field measurement technique using Pressure-Sensitive Paint (PSP) has been developed for acquiring global pressure images on wind tunnel models1,2. PSP makes use of the sensitivity of the luminescent materials

to the air pressure. So far, pressure field measurement with pressure taps has been conducted to capture pressure distribution on a model surface. This conventional measurement is very labor-intensive, and model preparation costs are high, when we investigate detailed pressure map. On the contrary, PSP measurement technique provides a simple and inexpensive way to obtain full-field pressure image on aerodynamic model surface with high spatial resolution.

PSP system has been developed for practical use at Wind Tunnel Technology Center (WINTEC) /Japan Aerospace Exploration Agency (JAXA). So far, the PSP measurement system has been applied to the 2 m × 2 m transonic wind tunnel3, 4 (TWT1) and the 1 m × 1 m supersonic wind tunnel (SWT1). The several verification tests were conducted, and the performance of PSP measurement has been demonstrated. Those results provided that the PSP measurement system allowed us to measure quantitatively and qualitatively pressure filed on a model surface. Our PSP measurement systems have already been utilized for the development of a domestically produced plane4.

As next phase, we engage upon development of low-speed PSP system5-8. Low-speed PSP technique is a promising measurement applicable to not only aerospace vehicles, but also automobile and train. However, there are some difficulties to accurately measure pressure distributions at low-speed flow, since the pressure difference on a model surface is small5. The PSP luminescent intensity is small at atmospheric pressure due to large oxygen quenching. * Researcher, Wind Tunnel Technology Center, Member † Researcher, Wind Tunnel Technology Center, Member ‡ Administrator, Program and Planning Office, Member § Associate Senior Researcher, Wind Tunnel Technology Center, Senior Member ** Associate Senior Researcher, Wind Tunnel Technology Center, Senior Member §§ Manager, Program Management and Integration Department, Senior Member †† Senior Researcher, Civil Transport Team, Senior Member

P

AIAA 2007-1065 45th AIAA Aerospace Sciences Meeting and Exhibit 8 - 11 January 2007, Reno, Nevada

45th AIAA Aerospace Sciences Meeting and Exhibit8 - 11 January 2007, Reno, Nevada

AIAA 2007-1065

Copyright © 2007 by the Authors. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

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Therefore, strong excitation light source is required for increasing signal noise ratio. Also, PSP measurement accuracy strongly depends on temperature correction technique, because PSP luminescent intensity depends not only on pressure, but also on temperature. Low-speed PSP system was constructed in JAXA 6.5 m x 5.5 m low-speed wind tunnel (LWT1). LWT1 has large test section and the distance between a model and PSP optical system becomes very far. Thereby, high-power LED system was manufactured for increasing PSP luminescence. This illuminator was brighter than conventional light source such as Xe arc lamp. And, low noise CCD camera (16-bit FFT type camera) was used for accurately measuring PSP images.

As temperature correction of PSP, PSP/TSP (Temperature-Sensitive Paint) combined system5 and PSP/IR (infrared camera) combined system6 have been applied. However, PSP/TSP combined system could not be applied to a half model. PSP/IR combined system was not for practical use, because overall measurement system including two different cameras was complicated, and the performance of an IR camera was restricted to material of window glass. Therefore, low temperature-sensitive PSP was applied in this experiment. Furthermore, error due to PSP temperature dependence was decreased by using wind-off PSP image immediately after shutdown of wind tunnel.

In this study, a large half-model with high lift device (HLD) was used. The HLD model was developed for research and development for next generation of civil transport aircraft. This project especially focuses on design of the high lift device by CFD and EFD research9-12. Specification of the half model is shown in Fig.1. The model size is 2.3 m in wing span and 4.9 m in fuselage length. The model was designed on the assumption of a civil transport aircraft for approx. 100 passengers. Our objectives is to develop the practical low-speed PSP technique at LWT1 and to acquire pressure images for understanding flowfield on a high lift device model. In this paper, our low-speed PSP technique is reported and the pressure patterns peculiar to the HLD model is presented.

Single-slotted flapSlat

Engine nacelle

Inboard Slat

4.9 m

2.3 m

Double-slotted flap

FTF

Single-slotted flapSlat

Engine nacelle

Inboard Slat

4.9 m

2.3 m

Double-slotted flap

FTF

Fig.1 Specification of half model with high lift devices.

II. PSP Measurement System for Low-speed test A. Pressure-Sensitive Paint

We used a commercial FIB-PSP purchased from ISSI (Innovative Scientific Solutions, Inc.). The PSP characteristics is shown in Fig.2. The FIB-PSP has small temperature sensitivity of its luminescent intensity. Pressure sensitivity of the PSP was insensitive to temperatures. As another candidate, LPS-B1 paint was considered7. It includes pyren dye and has very small temperature-sensitivity. However, it is excited at wavelength of UV (approx. 340nm) and less resistant to excitation light. On the other hand, the excitation wavelength of PtTFPP based FIB-PSP is from 380 to 550 nm and the PSP is resistant to photo-degradation. The luminescent peak wavelength of the PSP was 650 nm. In PSP measurement, pressure image is obtained from ratio of wind-on PSP image to wind-off one. As a general, pressure-sensitivity of PSP is expressed by Stern-Volmer equation. The equation is described as follows. It shows the relationship between pressure and the ratio of wind-on PSP image to wind-off one.

refrun

ref

ppBA

II

+= (1)

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Where, A and B are coefficient of Stern-Volmer equation. Two pressure-conversion techniques for PSP measurement, a-priori and in-situ method, are known. For a-priori method, coefficient A and B are obtained from calibration test in advance. Pressure images can be calculated by equation (1) without using pressure tap data. On the other hand, for in-situ method, A and B are estimated by least squared method from pressure tap data and PSP intensity ratio (Iref/Irun) around taps. In this study, an in-situ method was applied for converting PSP images to pressure ones. In practice, the equation (1) is non-linear. Thereby, it was extended to quadratic expression.

PSP was sprayed in the cart of LWT1. Normally, we applied PSP to a model in a dedicated paint room. However, the HLD model was so large and we could not spray the model in the room. As Figure 3 shows, a paint booth was set up and the staff sprayed the model with protective clothing. Total work day for building a paint booth, painting and drying was 4 days including weekend. PSP was sprayed on the upper surface of the wing and engine nacelle. The photo of PSP applied model is shown in Fig.4.

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0.70 0.80 0.90 1.00 1.10 1.20P/Pref (Pref=100kPa)

Iref/

I

0℃

5℃

10℃

15℃

20℃

25℃

30℃

(a) Pressure sensitivity

0.9

0.95

1

1.05

1.1

1.15

1.2

-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

T/Tref (Tref=20 degC, ＠100kPa)

I/Iref

(b) Temperature sensitivity

Fig.2 Pressure and temperature sensitivity of PSP.

Fig.3 Painting operation in LWT1. Fig.4 PSP applied model.

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B. Optical System The CCD camera and excitation illuminators were setup at the side wall of LWT1. We made a high-power LED

illuminator, because the power of commercial excitation-light source (Xe arc lamp) was not enough to irradiate PSP. The illuminator head (250mm × 250mm) had 1024 LEDs. Blue and UV emitting LED illuminator were manufactured. Emission peak for blue and UV LED was 460 nm and 405 nm, respectively. In this study, UV-LED illuminator was used. The emission intensity of LED illuminator is sensitive to surrounding temperature. So, the LEDs were air-cooled by a fan in order to stabilize the temperature of LEDs. Furthermore, photo-diode was installed in front of the LED head for stabilizing the LED emission intensity (See Fig.5). The intensity could be controlled by feed-back signal from the PD.

PSP luminescence was detected by a 16-bit CCD camera (Full Flame Transfer Type, HAMAMATSU PHOTONICS, K.K: ORCA-II-BT104). The image size is 1024 x 1024 pixels. The camera has low dark-noise due to cooling the CCD by a peltier device. The full-well electron of its CCD chip is 80,000. The camera was suitable for low-speed PSP measurement. 64 PSP images were acquired for a run in order to decrease CCD photon-shot noise. In front of a camera lens, optical filter was mounted and only PSP luminescence was detected. The exposure time of CCD camera and the data transfer time from the camera control unit to a PC was approx. 1-2 sec and 4.6 sec, respectively. Therefore, the total measurement time was about 10 minutes for a run.

Unfortunately, PSP luminescent intensity depends on both pressure and temperature. Therefore, error due to PSP temperature-sensitivity should be reduced for increasing measurement accuracy. As Bell proposed in Ref.13, temperature correction of PSP using wind-off PSP images immediately after wind tunnel shutdown was applied. The wind-off temperature immediately after tunnel shutdown is close to wind-on one. Thereby, this method can reduce measurement error due to temperature dependence of PSP.

The global and close-up measurement was conducted for acquiring overall and detail pressure image. The setup of global measurement is illustrated in Fig.6. To acquire PSP image on the upper side of main wing, CCD cameras and LED illuminators were mounted on the cart wall. PSP luminescence was acquired by the CCD camera through optical window. As mentioned above, PSP luminescence was sensitive to its own temperature. Thereby, temperature sensor was installed in the model. PSP measurement was started after attainment of stable temperature of the model. In close-up measurement, wing-tip, outer flap and junction between engine nacelle and main wing were individually visualized.

In this study, the optical setup was designed in advance by using virtual mock-up of the wind tunnel. From the CAD data of wind tunnels and models as shown in Fig.8, the optimum optical-setup at LWT1 was determined. This technique was very useful, because we could save time to setup the optical system.

Optical filter for cutting IR emission

Cooling fan

LEDs board

Air intake

Air intake

Fin for cooling

1024 LEDs

Exhaust airPhoto Diode

Optical filter for cutting IR emission

Cooling fan

LEDs board

Air intake

Air intake

Fin for cooling

1024 LEDs

Exhaust airPhoto Diode

(a) Photo of LED illuminator (b) Cross section of LED head. Fig.5 High-power LED illuminator.

Photo-Diode Sensor

American Institute of Aeronautics and Astronautics

CCD

CCD

LED IlluminatorLED Illuminator

Optical Window

Flow Direction

CCDCCD

CCDCCD

LED IlluminatorLED Illuminator

Optical Window

Flow Direction

Fig.6 Optical system for PSP measurement. Fig.7 High-power LED illuminator and

an irradiated half model.

Fig.8 Virtual mock-up of LWT1 for PSP system setup.

III. Data Reduction Data reduction process is briefly explained in this section. At first, acquired PSP images were averaged for

decreasing photon-shot noise and subtracted by dark images. The averaged PSP images were smoothed by imaging filter. Markers on wind-on and wind-off PSP images were detected, respectively, and image registration was conducted by using the detected marker position. After that, the processed PSP images were applied to a 3-D grid model.

Next, self-illumination (SI) correction was conducted14 – 16. In measuring PSP images on a complicated model (three-dimensional model), SI effect is not negligible, because PSP luminescence is affected by PSP emission at other locations of a model. The HLD model was composed of many parts. In processing images, a lot of grid node for the model was used. Thereby, so much calculation time for SI correction was required. In order to solve this problem, special processing tool for SI correction was developed17, 18. The calculation time for SI correction was improved. SI correction was applied in the junction between the main wing and body. After SI correction, PSP images were converted to pressure ones. An in-situ method was used. The in-situ calibration curve (PSP intensity ratio vs. pressure) were calculated by least squared method from pressure tap data and PSP intensity ratio (Iref/Irun) around taps. As mentioned in the previous section, wind-off PSP images immediately after shutdown of wind tunnel were used for decreasing error due to temperature dependence of PSP. Pressure images were calculated by using this calibration curve.

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IV. Experimental Results The flow speed was varied from 30 to 70 m/sec at the experiment. Angle of attack (AoA) was 5 deg. - 21 deg. 64

PSP images at wind-on and wind-off condition were acquired for a run. During test, the model temperature was changing. Thereby, 16 PSP images set were processed to diminish error due to PSP temperature dependence. As the following results show, pressure images at 60 m/s were clearly visualized by only 16 PSP images.

A. Measurement Accuracy Figure 9 shows an in-situ calibration curve at V=60 m/s and AoA=15deg.. The Root Mean Square (RMS) was

calculated from the difference between the in-situ curve and pressure tap data. At this condition, the deviation was approximately 0.16 in Cp. Cp for other cases (other AoA) at V=60m/s were about 0.2. Pressure variations on this HLD model were approximately 6 in Cp. Pressure images were clearly visualized with pressure resolution of 0.2 in Cp.

Comparison of PSP profile with pressure tap data is illustrated in Fig. 11. At every pressure tap lines, PSP data quantitatively agreed with pressure tap data. The obtained accuracy was satisfactory for the purpose of this experiment. Even more accuracy could be improved by temperature correction of PSP using 2 color paint including pressure- and temperature- sensitive molecule19 or an infrared camera6. Because major error source in the current test would be derived from temperature distribution due to a complicated configuration of the model composed of many elements.

Fig.9 Location of pressure tap line & in-situ calibration curve（ V=60m/sec, AoA=15deg.）.

Fig.10 Bird’s-eye pressure image at V=60m/sec and AoA=15deg.

S21 line

S22 line

S40 line

S61 line S62 line

S101 line

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Fig.11 Comparison of PSP profile with pressure tap data(V=60m/s, AoA=15deg).

S21 line S22 line

S40 line S61 line

S62 line S101 line

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B. Dependence of pressure patterns on angle of attack Pressure distributions at V=60 m/s and at the AoA (angle of attack) of 5 - 15deg. are shown in Fig.12. Suction

peak along the leading edge of main wing were seen, and the pressure became strong at large AoA. Pressure of the S21 line at AoA=15 deg achieved Cp= -4. Low pressure region due to separation vortex was seen at the wing tip and at the outboard edge of the outer flap (single-slotted flap). Their patterns were dependent on AoA. As Figure 13 shows, PSP data quantitatively agreed with pressure tap one at every AoA.

Close-up pressure image was also illustrated in Fig.14. Pressure variation due to separation vortex was qualitatively visualized with high spatial resolution, although number of pressure tap in the PSP image were not enough to increase measurement accuracy.

(a) AoA=15deg (b) AoA=10deg (c) AoA=5deg

Fig.12 Pressure images at V=60m/s.

(a) AoA=15deg (b) AoA=10deg (c) AoA=5deg

Fig.13 Comparison PSP data with pressure tap data at S21 line (V=60m/s).

Fig.14 Close-up pressure image at wing-tip (V=60m/sec, AoA=10deg.).

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C. Dependence of pressure images on flow speed Pressure distributions at AoA=10 deg and V=30-60 m/s were illustrated in Fig.15. With decreasing of flow speed,

the S/N (signal to noise ratio) got worse owing to small dynamic pressure. The dynamic pressure at V=30m/s was a quarter of that at V=60m/s. The measurement accuracy at V=30m/s was approximately 0.23 in RMS. Although measurement accuracy at that case was not high, pressure pattern was clearly recognized.

As Figure 16 shows, PSP data agreed well with tap data, although PSP profile at 30 m/s was fluctuating owing to low S/N. The data spread due to shot noise of a CCD is in reverse proportion to square root of PSP image number. Therefore, image quality of those pressure distributions can be further improved by increasing of number for processed PSP images.

(a) 60m/sec (b) 40m/sec (c)30m/sec

Fig.15 Pressure images at AoA=10 deg.

(a) 60m/sec (b) 40m/sec (c)30m/sec Fig.16 Comparison of PSP data with pressure tap data at S21 line (AoA=10 deg).

V. Conclusion Low-speed PSP measurement system for practical use was developed at JAXA/IAT/WINTEC LWT1. Pressure

images on the large-scale HLD half-model were clearly visualized. Obtained results were summarized as follows. (1)Painting system for large-scale wind tunnel was constructed, and the technical know-how were obtained. Optical

system including low-noise CCD camera and high power LED illuminators were developed and well functioned. These systems allowed us to acquire clearly pressure images in low-speed testing.

(2)Pressure images on the HLD model, which was built for R&D for next generation of civil transport aircraft, were clearly visualized. Pressure patterns peculiar to the HLD model were obtained.

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(3)Measurement accuracy was approximately 0.16 - 0.2 in Cp at 60m/s. The present PSP system could visualize pressure images at flow-speed of over 30 m/s. These results indicated that JAXA low-speed PSP system was a practical measurement tool to acquire pressure map on an aerodynamic model.

Acknowledgments The authors would like to gratefully thank Mr. Masatake Ito, Mr. Kentaro Ueta and Mr. Takuro Hashimoto for

constructing the PSP system at LWT1 and their valuable discussion.

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