Simultaneous Pressure and Velocity Field Measurement of Pseudo-Shock-Wave Using PSP and PIV

Transcription

1 5th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 9-12 January 212, Nashville, Tennessee AIAA Simultaneous Pressure and Velocity Field Measurement of Pseudo-Shock-Wave Using and PIV Shunsuke Koike 1 JAXA/Wind Tunnel Technology Center, Chofu, Tokyo, , Japan Junichi Osawa 2 Tokyo University of Agriculture and Technology, Koganei, Tokyo , Japan Kazuyuki Nakakita 3, Hiroyuki Kato 4 JAXA/Wind Tunnel Technology Center, Tokyo, Chofu, , Japan and Masaharu Kameda 5 Tokyo University of Agriculture and Technology, Koganei, Tokyo , Japan A combined system of time-resolved PIV and unsteady was applied to an unsteady internal supersonic flow field including a pseudo shock wave. Dry ice was applied to the PIV tracer in order to prevent the contamination of the fast response. The combined system measured the velocity and pressure fields simultaneously at sampling rate of 2 khz. The velocity and pressure fields simultaneously measured clarified the three-dimensional unsteady phenomena of the pseudo shock wave. The interaction between the PIV, the, and the flow conditions are briefly discussed. B I. Introduction OTH pressure distribution on a body and velocity distribution in a flow field help us to understand the fluid dynamics around a fluid machinery. Characteristic pressure distributions on a body in a flow field are mostly caused by characteristic vortices and waves. Specifying the vortices and the waves from the velocity distributions are useful to determine the cause of the characteristic pressure distributions. Understanding of the flow mechanism helps us to determine the cause of the fluid dynamics problems. Generally, it is much more difficult to understand the mechanism of unsteady flow fields than that of steady flow fields. One of the reasons is the difficulty of the measurement of unsteady flow fields. When steady flow fields are investigated, it is appropriate to measure the pressure and the velocity fields separately since the both fields do not change whenever the measurement are performed. However, it is not enough to measure the pressure and the velocity fields separately in order to investigate unsteady flow fields since the pressure and velocity fields of the unsteady flow change at all times. Hence, it is important to measure simultaneously the pressure and velocity distributions at Flow Figure 1. Schematic figure of pseudo-shock wave. 1 Researcher, Aerospace Research and Development Directorate, skoike@chofu.jaxa.jp. Member AIAA. 2 Graduated Student, Department of Mechanical Systems Engineering. 3 Associate Senior Researcher, Aerospace Research and Development Directorate, nakakita@chofu.jaxa.jp, Senior Member AIAA. 4 Associate Senior Researcher, Aerospace Research and Development Directorate,.hirok@chofu.jaxa.jp, Member AIAA 5 Professor, Department of Mechanical Systems Engineering, kame@cc.tuat.ac.jp, Member AIAA. 1 Copyright 212 by the authors. Published by the, Inc., with permission.

2 appropriate sampling rate in order to understand the mechanism of unsteady flow fields and determine the cause of the fluid dynamics problems. Recently, fast response Pressure-Sensitive Paint () is applied to several unsteady flow fields The fast response enables us to measure time resolved pressure distributions of unsteady flow fields at time resolution of several khz. On the other hand, time resolved Particle Image Velocimetry (PIV) is also applied to several unsteady flow fields to measure time resolved velocity distributions at time resolution of several khz Both techniques are useful to analyze unsteady flow fields. It is desirable that the both time resolved pressure and velocity distributions are measured simultaneously using a combined system with the fast response and the time resolved PIV. The correlation of the both pressure and velocity fields are useful to analyze the unsteady flow fields. In this study, the simultaneous measurement of the fast response and the time resolved PIV was performed. Generally, the contamination of the tracer particles in PIV for coating is one of the biggest problems to use the both measurement techniques simultaneously. The oil, alcohol and solid particles which are commonly used in PIV damage the faculty of the sensor, physically and chemically. In order to solve this problem, solid carbon dioxide, namely, dry ice was applied to the PIV tracer 21, 22 since the dry ice particles sublimes in normal atmospheric conditions and physical and chemical damages for the coating are negligible. The combined system with the fast response and the time resolved PIV using the dry ice particles was applied to measure the internal 14, 15 supersonic and subsonic flow fields with the oscillating and traveling shock waves, pseudo-shock wave (PSW) shown in Fig. 1. The pressure distributions on the side wall of the test section and the velocity distributions in the center plane of the duct were measured. II. Time-Resolved-PIV A. Dry ice particle The key technique for the combined system with and PIV was the tracer particles in PIV. In order to prevent the contamination for the coating with the PIV tracer, solid carbon dioxide, namely dry ice was used as the tracer particles. Dry ice particles were formed to inject liquid carbon dioxide (LCO2) from a Siphon type LCO2 bombe. When the LCO2 is injected from the small orifice, the partial LCO2 become solid phase because the partial LCO2 become gaseous phase absorbing the heat from other part of LCO2 and the expansion of the gaseous CO2 decreases the temperature around the LCO2. In this experiment, LCO2 were injected from the orifices of.5 mm diameter for the preliminary experiment and 1. mm diameter for the PSW measurement. The stagnation pressure of LCO2 was about 6 MPa for the both experiments. The mass flow rate of CO2 was estimated to be about 6.6 g/sec for the.5 mm orifice and 26.4 g/sec for the 1. mm orifice from the result of a preliminary 22 experiment and the temperature. Figure 2 shows the supplying system of dry ice particles for the PSW measurement. Two injectors were used in the experiment. A metal tube with several holes was attached to the orifice block in order to improve the uniformity of the distribution of the dry ice particles. The diameter of the dry ice particles injected from.5 mm orifice without the tube was estimated to be 1.2 m in the previous research 22. However the diameter of the dry ice particles was larger than 1.2 m in this experiment because the particle size increased in the metal tube. Although the large particle is appropriate for the visualization especially when the laser power is low, the traceability of the particles becomes wrong. The control of the size of the dry ice particle is one of the important issues for the simultaneous measurement of PIV and. B. Visualization and analyzing system for PIV Two-dimensional Time-Resolved-PIV system 2 was used. A high repetition double pulsed Nd:YAG laser (LDP-2MQG DUAL DIODE PUMPED LASER, LEE LASER Inc., 1mJ/pulse at 1kHz) was used as the light source. The repetition rate was 2 khz in the PSW measurement. The power of laser was about 8 mj / pulse at the repetition rate of 2 khz. Laser sheet was produced using a cylindrical lens. The focal length of the cylindrical lens was -25 mm. The interval of the successive laser pulse (t) was set at 1.8 s. A high speed CMOS camera (Phantom V71, Vision research) with a camera lens (Nikkor 15 Liquid CO 2 from CO 2 tank Orifice (D=1mm) CO 2 injector Metal tube with bleed holes Cap with hole CO 2 particle Figure 2. Injector of dry ice particles. 2

3 mm f/2, Nikon) was used for the recording of the scattering light from the tracer particles. Since the sampling rate of the velocimetry was 2 khz, the recording of the particle images was conducted at 4 k frame-per-second (fps). The resolution of the camera was 128 pix x 8 pix at the recording rate of 4 kfps. 1, pairs of pictures were taken for all cases. In order to cut the illumination for and the luminescence from the, a band-pass filter for the wavelength of 532 nm was attached on the lens for the PIV camera. The camera and laser systems were controlled using signal generator and Davis 7.2 (Lavision) with a high speed control module. The signal generator for PIV was also used for the synchronization of and PIV system. The more detail of the synchronization of PIV and are described in the section of the experimental setup for PSW measurement. The analyzing software Davis 7.2 was used to calculate the velocity vectors. An averaged background image was subtracted from the particle images as the pre-process. The interrogation area was 32 pix x 32 pix with 5 % overlap. The multi pass algorithm in the Davis 7.2 was used for the calculation. III. Fast-Response A. Anodized Aluminum is a molecular sensor based on oxygen quenching of its luminescence. Luminescence intensity from luminophore is varied by the environmental oxygen partial pressure. Conventional, which consist of luminophore and polymer binder, have their typical response time of order 1 sec. For unsteady measurement, it is necessary to use much faster. Anodized aluminum (AA-) is a binder-free consisted of anodized aluminum layer and luminophore without polymer binder. AA- is established by Asai et al. 8 and modified by Sakaue et al. 9 Anodized aluminum layer is porous aluminum oxide layer formed by electrochemical process in sulfuric acid known as anodization. The surface of anodized aluminum is constructed by small porous cell shown in Fig. 3. Luminophore in this study was tris(4,7-diphenylphenanthroline)ruthenium(ii) dichloride ([Ru(dpp)3]Cl2). It directly absorb on porous aluminum oxide layer. After absorbing luminophore on anodized aluminum surface, hydrophobic treatment 1 was applied to AA-. Stearic acid was coated on AA- surface. This treatment is reported that it improves the original hydrophilic surface to hydrophobic and reduces characteristics aging. However, AA- pressure sensitivity became small after this treatment. AA- has extremely fast response characteristics, which is the order of 1 s 11,12,13. It has enough fast for unsteady measurement. B. Visualization and analyzing system for Unsteady measurement system includes a high-speed camera, a high-power illumination light sources, and optical apparatus. The images were recorded with high-speed CMOS camera (Phantom V7.3). The recording was conducted at spatial resolution of 8 pix x 32 pix at frame rate of 2 k frame-per-second (fps). The exposure time was 498 s. The luminescence optical filter (HOYA O58) was installed in front of the high-speed camera to transmit the luminescence wavelength centered at 62 nm and cut the blue and green illumination light component for and PIV. A high-power blue laser diode (Sumitomo Electric Industry, BLM-5-H8D) was used as the illumination light source for. It consists of 14 laser diode pieces and their laser lights are bundled to on output. Its wavelength distributes nm. Its total illumination laser power is 5W. Typical stability during 1 sec is less than.5 %. Laser light is guided to illumination light head, which adjusts the illumination area and improves uniformity of laser light, through a liquid light guide. pore cell Anodized Aluminum Layer (a) Aluminum Base (b) 1nm Figure 3. Structure of anodized aluminum layer. (a) schematic drawing of porous anodized aluminum layer, (b) scanning electron microscope (SEM) image of anodized aluminum surface. 3

4 C. Data reduction method Figure 4 is the flow chart of the data processing. There are two parts of data processing, which are pressure calculation process and calibration one. At first, the pressure calculation process is described. There are two types of acquired images, reference and windon images. Reference images are intensity images under atmospheric pressure around 1 kpa. Wind-on images are time-series images of intensity acquired in the test time. Both images are subtracted dark component. Then, reference images are averaged to single reference image, I ref. Wind-on images keep time-series images. Time series I ref /I ratio images are calculated using the reference image and time-series wind-on images. Image registration between reference and wind-on image was not applied on present data processing assuming the test model deformation was small. Finally, I ref /I ratio images are processed to time-series pressure images using the relation between I ref /I and pressure and characteristics provided from calibration. Theoretically the relation between I ref /I and pressure is represented by following Stern-Volmer relation; I ref P A B I Pref (1) A, B = Stern-Volmer coefficients I = intensity acquired by high-speed camera P = pressure ref = reference condition, 1kPa Actual characteristics tend to have nonlinear pressure sensitivity. In this study, second order of the universal expression of Stern-Volmer was applied to fit the present AA- characteristic; P P Reference images Dark subtraction Iref image (Averaged) Pressure calculation 2 I ref I ref 1 c 2 c3 I images (Time series) I ref /I ratio images (Time series) Wind-on images Dark subtraction 2 I ref I ref 1 c2 c3 c Pressure distribution images (Time series) c ref I I (2) c1-c3 are the unknown constant and decided through calibration. Data processing on calibration process is almost same with the pressure calculation above. The difference is that calibration images reduce to an averaged image and a I ref /I ratio image is not time-series. pressure sensitivity is calculated by the I ref /I ratio image and calibration pressure measured by a pressure gage using least square fitting to Eq. (2). P P ref I I Reference images Calibration images Pressure Gage Dark subtraction I ref image (Averaged) Calibration I ref /I ratio image c 1, c 2, c 3 Dark subtraction ref ref 1 c2 c3 AA- has nonuniformity of pressure sensitivity. Hence, the pressure sensitivity needs to provide locally to calculate pressure quantitatively. Thus the calibration process is also applied locally and repeated all over the image. Figure 5 is a schematic of the definition for local Figure 5. Schematic of the definition for local calibration and data processing area. Local pressure calibration and data processing area. Local sensitivity was calculated using data of the region of 7 7 pressure sensitivity was calculated using the data pixels, which color is red and orange in Fig. 5. Calculated of 7 7 pixels. Calculated local pressure local pressure sensitivity was applied to only 2 2 pixels sensitivity was applied to only 2 2 pixels at the at the center, which color is red in Fig. 5. The red area in Fig. center. 4 P P ref I image (Averaged) 2 I c I Figure 4. Flow chart of data processing. Area for local calibration 2 pixels 7 pixels I I 2 pixels 7 pixels P, P ref Area for data processing

5 5 is never overlapped. However, the orange area is overlapped with that of the neighbor red area. The reason for using larger number of pixels for calibration area is to average large number of pixels and decrease the contribution of shot noise on each pixel to the pressure sensitivity calculation process. IV. Preliminary experiment In order to investigate the influence of the dry ice particles on the AA- coating, the preliminary experiment was conducted. In the preliminary experiment, the sensitivity expressed by the Eq. (1) was compared for the clean plate and the plate contaminated with the dry ice particles. First, the sensitivity of clean was measured. Second, the dry ice injection test was conducted. Third, the sensitivity of the plate contaminated with the dry ice particles was measured. Finally, the both sensitivity was compared. Figure 6 shows the experimental setup of the dry ice injection test. The dry ice was injected to the plate vertically and in parallel. The L shows the distance between the plate and the exit of the injector. It was set at 2 mm and 4 mm. Figure 7 shows the sensitivity of the before and after the injection test. The circle and triangle symbols show the relation between the pressure ratio and intensity ratio of the plate before and after the test. The triangle symbols agree with the circle symbols very well. Table 1 shows the sensitivity of the for the all cases. The difference of the sensitivity before and after injection was very small and less than or equal to.1 %/kpa. The measurement conditions of the PSW are similar to those parallel injection cases. Hence, the contamination of the dry ice particle on the coating is negligible in the PSW measurement. In order to investigate the worst case, the L was set at 5 mm and the dry ice was injected to the plate vertically. In this case, the dry ice particles lay and remained on the plate as shown in Fig. 8. Figure 9(a) and (b) shows the intensity images of the plate before and after the injection test. The intensity of the plate was uniform before the injection test as shown in Fig. 9(a). However, the intensity of the plate was not uniform after the injection test. In Fig. 9(b) the intensity of the luminescence is high in the region close to the center of the impinging point. Figure 1 shows the sensitivity of the before and after the injection test. In the region close to the impinging point, the sensitivity of the decreased. If the dry ice particles physically had broken the coating, the intensity of the would have decreased. However, the intensity of the luminescence increased. Hence it is considered that the CO2 remain in the porous of the AA- surface prevent the oxygen quenching and the sensitivity of the decreased. Parallel Nozzle D =.5 mm sample Figure 6. Schematic of the dry ice particle injection test. Intensity ratio: Iref/I Nozzle Vertical Parallel-4mm L CO2 L CO2 Table 1. Sensitivity of the plate. sample 65mm sample 65mm φ5mm φ2.5mm Nozzle Before CO2 injection After CO2 injection Pressure ratio: P/Pref Figure 7. Sensitivity of the plate before and after the injection test. Pressure-sensitivity [%/kpa] Testing condition Before CO 2 injection After CO 2 injection Vertical-2mm Vertical-4mm Parallel-2mm Parallel-4mm

6 A B C D Figure 8. Picture of the injection test (L = 5 mm). (a) Before injection (b) After injection Figure 9. Intensity images of before and after injection test. V. Experimental setup for PSW measurement A. Wind tunnel and arrangement of PIV and systems Figure 11 shows a schematic of the experimental setup. Experiments were conducted using a suction type supersonic wind tunnel. Dry air at atmospheric pressure and temperature in an air bag was inhaled into a vacuum tank through a two-dimensional contoured nozzle and a test section. A seeding chamber was set at the entrance of the nozzle to supply the dry ice particles into the dry air. Liquid CO2 were injected from the two orifices of 1. mm diameter. The tube with several holes was attached to the orifice block to improve the uniformity of the distribution of the dry ice particles. The orifices were located at 5 mm and 1 mm from the bell mouth of the nozzle. The bottom positions of the tubes were 2 mm and 7 mm in height from the center of the nozzle. Intensity ratio: Iref/I Before CO2 injection A - after CO2 injection B - after CO2 injection C - after CO2 injection D - after CO2 injection Pressure ratio: P/Pref Figure 1. Sensitivity of the plate before and after the injection test (L =5 mm). The dry ice particles remain on the plate. Air bag dry air atmospheric pressure Liquid CO Test section 2 cross section : 8x8 mm Liquid CO 2 length : 43 mm Acrylic window Valve M=2 nozzle Vacuum tank PIV laser coated area laser Acrylic window High speed camera (PIV) High speed camera () Figure 11. Schematic of experimental setup for PSW measurement. 6

7 43 Kulite-4 Kulite-1 Kulite-2 Kulite Kulite Unit :mm :Pressure tap : Marker Figure 12. Dimensions of markers and pressure taps on coated side wall. The designed Mach number of the supersonic nozzle was 2.. Side wall of the test section was coated with the fastresponse, anodized aluminum (AA-). There were five pressure taps to evaluate data as shown in Fig. 12. Kulite XCQ-62-5A pressure transducers were installed at each pressure taps on the coated side wall. Another side and bottom walls were made of clear acrylic resin to obtain the and PIV images and to illuminate with a laser sheet. The cross section of the test section was 8 mm x 8 mm. The pressure in the vacuum tank was set at 45-5 kpa to generate the PSW and to minimize the supersonic flow duration to reduce the temperature decrease until PSW arrival. Figure 11 also shows the arrangement of PIV and measurement system. Upper figure shows the side view and the lower figure shows the top view. The measurement area of the PIV was illuminated with the laser light sheet from the bottom window. The scattering light from the particles were recorded with the high speed CMOS camera through the side window. The wall coated with the was illuminated with the blue laser from the side window. The images were also recorded with the high speed CMOS camera through the side window. B. Synchronization system Figure 13 shows the schematic of the synchronization system for PIV, and pressure transducers. The combined system was controlled with the synchronizer, high speed controller in Fig. 13 and Davis 7.2 (Lavision) with a high speed control module. The camera was controlled by the signal from the high speed controller to the laser Q-switch, which was delayed by a delay generator (DG535, Stanford research systems, Inc.). The starting trigger for the measurement sequence was outputted based on the voltage signal from the pressure transducer. When the wind tunnel was started, the wall pressure decreased and the voltage from the pressure transducer decreased. The triggered signal was outputted from the pulse generator to the synchronizer when the voltage from the pressure transducer was lower than 2 V. In the result, the time at which the trigger signal is outputted is determined as ms. Figure 14 shows the timing chart of PIV and. The frame rate of the camera was 2 kfps. The exposure time of the camera was 498 s. The was illuminated continuously using the blue laser during the test time. The interval of the successive laser pulses t was 1.8 s for PIV. The frame rate of the PIV camera was the double of the camera, 4 kfps. DG 535 setting A=T+( ) s B=A+1 s C=T+ s D=T+2s USB Ethernet PIV PC Digital thermometer Trigger High speed Trigger signal controller (Synchronizer) cam1 Q2 Q1 T DG535 (Delay Generator) C C D Trigger F-sync Trigger F-sync PIV CAM CAM Ethernet PC Pressure transducer (7) kulite (1-5) kulite (6) CO2 supply Laser2 Laser1 LEE LASER (PIV Laser) WE7 Trigger (Data Logger) DC Amplifier (1-7) kulite (1-6) Pressure transducer (7) Kulite-3 Pulse Generator Trigger signal Figure 13. PIV//Pressure transducers synchronization system. 7

8 Delay CAMERA PIVCAMERA LASER 1 LASER 2 t Figure 14. Timing chart of PIV and. VI. Result A. Pseudo-shock wave (PSW) measurement The images of the scattering light from the dry ice particles are shown in Fig. 15(a)-(c). The concentration of the dry ice particles was too high at the time around the starting point of the wind tunnel as shown in Fig. 15(a). After about 1 ms, the appropriate images for the PIV could be obtained although the number of the particles was not so large. The typical particle images for the uniform supersonic flow and the flow field with the PSW were shown in Fig. 15(b) and (c). It was difficult to disperse the dry ice particles uniformly in this experiment. The number density of the dry ice particles is not so high in the both images. Seeding method for the dry ice particles should be improved in the next trial. When the oil particles are used for the similar flow fields, the observation window is contaminated by the oil droplets 22. As the result, the measurement time is limited. In this measurement, the contamination of the observation window was not observed. It is advantage of the dry ice particles for the measurement of the flow fields in the narrow duct. Figure 16 shows the contour figures of the pressure distribution measured with and the velocity vectors measured with PIV. The color of the velocity vector is the magnitude of the velocity vector. The bottom figures show the measurement area of the and PIV and the schematic of the boundary layer on the cross section of the duct. The t in the figures shows the time from the trigger point. The time history of pressure and magnitude of the velocity vector at the several points of y = mm are shown in Fig. 17(a) and (b) in order to help the understanding of the Fig. 16. Since the velocity data was noisy, the moving average for the 2 points is shown in Fig. 17(b). After t = 1 s, the pressure increase and the velocity decrease can be observed in Fig. 17. Globally, the time history of the pressure increase agrees with the velocity decrease as shown in Fig. 17. This agreement roughly indicates the success of the synchronization of the and PIV systems. The both pressure contours and the velocity vectors clearly show the change of the flow fields in the test section. As shown in Fig. 16, the flow field was supersonic in the measurement region at t = 5 ms. The pressure and velocity distributions were almost uniform at t = 5 ms. At t = 755 ms and 95 ms, the pressure increase could be observed in the downstream region. In those figures, the pressure in the region close to the upper or lower wall was higher than that on the y = mm line at the same location in the streamwise direction. It was caused by the thick Figure 15. Particle images. (a) Uniform flow with large amount of dry ice particles, (b) Uniform flow, (c) pseudo-shock waves. 8

9 PIV Flow Boundary layer Figure 16. Contour of pressure distribution and velocity vector. 9

10 Pressure, kpa x=-3 x= x= time, s (a) Pressure 4 x=6 x=3 2 x= x=-3 x= time, s 3 4 (b) Velocity Figure 17. Time history of velocity and pressure at y = mm. U, m/s 6 boundary layer at the corner of the duct. On the other hand, at t = 1155 ms and 1725 ms, the pressure on the y = mm line was higher than that in the region close to the upper or lower wall at the same location in the streamwise direction. The latter type was observed at many times. As shown in the bottom figure of Fig. 16, the thick boundary layer on the y = mm line was produced by the secondary flow in the boundary layer on the side wall of the two dimensional supersonic nozzle. The thick boundary layer on the y = mm line caused the pressure increase of the latter type. At t = 1725 ms, the velocity vectors around x = mm and y = mm were high and indicated the supersonic flow although the pressure increase could be observed at those points. This result clearly indicates the threedimensionality of the flow fields. At t = 2185 ms, the main flow was decelerated by the shock wave around x = mm. The position of the shock wave was not clear in the velocity vector figures since the spatial resolution and the traceability of the particles were not enough. After t = 275 ms, the wall pressure was uniformly high. The velocity vector decreased to the subsonic speed. As described above, the simultaneous unsteady pressure and velocity data clarify the time history and the three-dimensionality of the flow fields. B. Quantitative evaluation of interaction between and PIV Figure 18 shows the conceptual figure of the interaction between, PIV, and flow conditions. In this measurement, the influence of the measurement on the flow conditions was negligible. The influence of the luminescence and the illumination for the measurement on the PIV was also negligible. Improvement of the seeding method for the dry ice particle is the most important issue for the PIV in order to increase the quality of the velocity data. Influence of the dry ice particles on the data and the flow conditions were observed in the pressure and velocity data. Both interactions are described below. Figure 19 shows the comparison between the time histories of the pressure measured with the and the pressure transducer (Kulite) at the point around the Kulite- 2 in Fig. 12. The measured wall pressure is normalized by the initial pressure. The initial pressure was same as the stagnation pressure in this measurement. The large fluctuation was observed in the data around the t = s. Flow conditions Increase of noise Decrease of flow velocity PIV Figure 18. Conceptual figure of the interaction between, PIV and Flow conditions. Wall pressure/initial pressure Wall pressure/initial pressure Kulite time, s Kulite time, s Figure 19. Time history of normalized pressure for a PSW case. Upper figure shows time history of the wall pressure from -.5 s to 4.5 s. Lower figure shows that from 2.5 s to 3. s.

11 It was caused by the high concentration of the dry ice particles as shown in Fig. 15(a). The offset between the and the Kulite lines was not caused by the dry ice particles. It is clarified in the next Fig. 2. From the lower figure of Fig. 19, it is clear that successfully acquired the pressure fluctuation caused by the PSW. The influence of the dry ice on the response ability of the was small. In order to evaluate the influence of the PIV on the data, the uniform flow was measured with several measurement conditions. In Fig. 2, the time histories of the wall pressure measured with the and the pressure transducer (Kulite) at the same point (Kulite-2) were shown for several measurement conditions. The blue lines and the caption PIV and correspond to the simultaneous measurement of and PIV. The black lines and the PIV Laser and correspond to the with the PIV laser without the dry ice particles. The red lines and the correspond to the without PIV Laser and the dry ice particles. The green lines and the PIV particles and correspond to the with the dry ice particles without the PIV laser. From the comparison between the red lines measured with the and the pressure transducer, it is clear that the most part of the offset between the and the pressure transducer was not caused by the dry ice particles. In this measurement, the humidity and the temperature on the surface were not perfectly same as those in the calibration process. It is considered that those differences produced the offset between the and the pressure transducer. The red line of the is slightly increasing in Fig. 2. The temperature on the measured wall was decreasing in this experiment. The lower temperature increases the intensity of the luminescence from the and decreases the measured pressure. Thus the influence of the temperature was not the reason of the increase of the red line. Hence we consider that the increase of the red line was caused by the humidity change. The difference between the black and red line for was small in Fig. 2. It means that the influence of the PIV laser on the was negligible. On the other hand, the influence of the dry ice particles is easily observed in the lower figure of Fig. 2. The average of the green and blue lines of in Fig. 2 is slightly higher than that of the red and black lines. The reason is considered as follows. The fog of the dry ice particles slightly interrupted the luminescence from the to the camera and decreased the intensity of the measured intensity of the luminescence. As the result, the averaged pressure measured with the increased as shown in Fig. 2. The fluctuation of the blue and green lines of in Fig. 2 is larger than that of the red and black lines. Intermittent impinging of CO2 on the surface increases the intensity of the luminescence and decreases the pressure intermittently. The intermittent interruption of the luminescence by the dry ice particles intermittently increases the pressure. It is considered that these are the reasons of the fluctuation of the green and blue lines. Table 2 compares the average and the standard deviation of the measured pressure normalized by the initial pressure from t = 1. to 3. s. In Table 2, the difference of the averages and the standard deviations of the normalized pressure measured with the between the several measurement conditions were small and less than.1 (about 1 kpa) for the average and.3 (about.3 kpa) for the standard deviation, respectively. In the PSW measurement, the main fluctuation was larger than.1 (about 1 kpa). Hence the combined system could successfully measure the pressure fluctuation caused by the PSW as shown in Fig. 19. In Fig. 2 and Table 2, the pressure measured with the pressure transducer (Kulite) was hardly changed by the dry ice particles. It means that the influence of the dry ice particles on the pressure fields was negligible. However, the velocity fields were changed by the injection of the dry ice. Figure 21 shows the normalized uniform flow velocity. The vertical axis shows the y normalized by the duct width. The horizontal axis shows the averaged velocity of the uniform flow normalized by the theoretical velocity. Here, theoretical velocity means that the velocity calculated from the wall pressure, Wall pressure/initial pressure Wall pressure/initial pressure PIV and PIV Laser and PIV Particles and Kulite time, s time, s Figure 2. Time history of normalized pressure for uniform flow cases. The blue lines correspond to the simultaneous measurement of and PIV. The black lines correspond to the with the PIV laser without the dry ice particles. The red lines correspond to the without PIV Laser and the dry ice particles. The green lines correspond to the with the dry ice particles without the PIV laser.

12 Table 2. Influence of dry ice particle and PIV laser on the pressure measurement. PIV+ PIV Laser and PIV Particles and Kulite average average Kulite standard deviation standard deviation *Time=1. s - 3. s, wall pressure/initial pressure stagnation pressure, and stagnation temperature assuming the isentropic condition. The black line shows the theoretical velocity. The blue and red line shows the averaged velocity measured with PIV using a single particle injector and twin particle injectors, respectively. Figure 21 clearly shows that the injection of the dry ice particles decreased the averaged velocity. The large amount of the dry ice and the gaseous CO2 decreased the average velocity largely. In the twin injector case, the average velocity was decreased about 5 % of the theoretical velocity. The same influence of the dry ice particles had been reported in the previous research 22. The decrease of the averaged velocity is caused by the decreasing of the total temperature and the specific heat ratio caused by the gaseous CO2. This is the biggest penalty of the simultaneous measurement of the and the PIV using the dry ice particles. Y position / Duct width VII. Conclusion Number of CO2 injector Theory 1 2 A combined system of time-resolved PIV and unsteady was applied to an unsteady internal supersonic flow field including a pseudo shock wave. Dry ice was applied to the PIV tracer in order to prevent the contamination of the fast response. The combined system measured the velocity and pressure fields simultaneously at sampling rate of 2 khz. The velocity and pressure fields simultaneously measured clarified the unsteady three-dimensional phenomena of the pseudo shock wave. The interaction between the PIV, the, and the flow conditions are briefly discussed. In this measurement, the influence of the measurement on the flow conditions and PIV were negligible. Although the noise of the was slightly increased by the dry particles, the level of the noise was smaller than the main pressure fluctuation caused by the pseudo shock wave. Hence the in the combined system successfully resolved the pressure fluctuations of the pseudo shock wave. The injection of the CO2 decreases the total temperature and the specific heat ratio. As the result, the velocity of the uniform flow was decreased about 5 % of the original uniform flow velocity. The monitoring and the controlling of the flow conditions are the important issues for the simultaneous measurement of PIV and using the dry ice particles. Acknowledgments This work was supported by Grant-in-Aid for Scientific Research (B) The several experimental setups were made by Sanji Kawaguchi. We wish to express our gratitude to them. References 1 Kameda, M., Tabei, T., Nakakita, K., Sakaue, H., and Asai, K., Image measurements of unsteady pressure fluctuation by a pressure-sensitive coating on porous anodized aluminium, Measurement Science and Technology, Vol. 16, No. 12, 25, pp Kameda, M., Seki, H., Makoshi, T., Amao, Y., and Nakakita, K., Unsteady Measurement of a Transonic Delta Wing Flow by a novel, AIAA , Time averaged velocity at x=mm / Theoretical velocity Figure 21. Uniform flow velocity with the dry ice particles. Black line shows the theoretical velocity calculated from wall and stagnation pressure and stagnation temperature assuming the isentropic condition. Blue line shows the measured velocity using the single particle injector. Red line shows the measured velocity using the twin injectors.

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