Pressure Sensitive Paint Method Research Articles

Triple decomposition and sparse representation for noisy pressure-sensitive paint data

Triple decomposition is a powerful analytical method for a deep understanding of the flow structure by extracting the mean value, organized coherent motion, and stochastic part from a fluctuating quantity. Here, we perform the triple decomposition of the spatial two-dimensional data, especially pressure-sensitive paint (PSP) data, since the PSP method is widely used to measure the pressure distribution on a surface in wind tunnel testing. However, the PSP data measuring near atmospheric pressure contain significant noise, and this makes it difficult to conduct the decomposition. To construct phase-averaged data representing an organized coherent motion, we propose a relatively simple method based on a multi-dimensional scaling plot of the cosine similarity between each PSP datum. Then, the stochastic part is extracted by selecting phase-averaged data with an appropriate phase angle based on the similarity between the measurement and phase-averaged data, and the PSP data are successfully decomposed. Moreover, we consider sparse optimal sensor positions, in which the data are effectively represented, based on the stochastic part as a data-driven approach. The optimal sensor positions are determined as a combinatorial optimization problem and estimated using Fujitsu computing as a service digital annealer. We reconstruct the pressure distribution from the pressure data at the optimal sensor positions using the mean value, organized coherent motion, and stochastic part obtained from the triple decomposition. The root mean square error between the pressure measured by a pressure transducer and the reconstructed pressure obtained by the proposed method is small, even when the number of modes and sensor points is small. The application of PSP measurement is expected to expand further, and the framework for calculating triple decomposition and sparse representation based on the decomposition will be useful for detailed flow analysis.

Temperature Dependency Model in Pressure Measurement for the Motion-Capturing Pressure-Sensitive Paint Method.

Pressure-sensitive paint (PSP) has received significant attention for capturing surface pressure in recent years. One major source of uncertainty in PSP measurements, temperature dependency, stems from the fundamental photophysical process that allows PSP to extract pressure information. The motion-capturing PSP method, which involves two luminophores, is introduced as a method to reduce the measurement uncertainty due to temperature dependency. A theoretical model for the pressure uncertainty due to temperature dependency is proposed and demonstrated using a static pressure measurement with an applied temperature gradient. The experimental validation of the proposed model shows that the motion-capturing PSP method reduces the temperature dependency by 37.7% compared to the conventional PSP method. The proposed model also proves that a PSP with zero temperature dependency is theoretically possible.

Data-driven optimal sensor placement for high-dimensional system using annealing machine

We propose a novel method for solving optimal sensor placement problem for high-dimensional system using an annealing machine. The sensor points are calculated as a maximum clique problem of the graph, the edge weight of which is determined by the proper orthogonal decomposition mode obtained from data based on the fact that a high-dimensional system usually has a low-dimensional representation. Since the maximum clique problem is equivalent to the independent set problem of the complement graph, the independent set problem is solved using Fujitsu Digital Annealer. In contrast to existing greedy methods, which select the optimal point at each step and never reconsider the point selected previously, the proposed method is superior because it is able to find the optimal set of points. As a demonstration of high dimensional system, the pressure distribution measured by the pressure-sensitive paint method, which is an optical flow diagnose method, is reconstructed from the pressure data at the calculated sensor points. The root mean square errors (RMSEs) between the pressures measured by pressure transducers and the pressures reconstructed from the proposed method, an existing greedy method, and random selection method are compared. The similar RMSE is achieved by the proposed method using approximately 1/5 number of sensor points calculated by the existing method. This method is of great importance as a novel approach for optimal sensor placement problem and a new engineering application of an annealing machine.

Enhancement of blade tip cooling with different position on tip cooling slot

One of the leading causes of thermally induced failure in gas turbine blade tip is a tip leakage flow. To protect blade tip efficiently from strong tip leakage flow, slot cooling is adopted in blade tip considering the application of additive manufacturing. For slot cooling scheme in blade tip, slot location ranging from PS slot to SS slot is a crucial role in film cooling effectiveness of blade tip. Therefore, we investigated the effect of the cooling-slot location on film cooling effectiveness and flow characteristics of blade tip with slot cooling considering the application of additive manufacturing. The local film cooling effectiveness on the blade tip floor and upper surface of the rim are obtained using pressure sensitive paint method. The case of coolant discharge from the PS slot was both stable and evenly spread, resulting in an outstanding coolant coverage of the entire tip regions. However, under severe effect of hot main gas flow behavior, the case of the SS slot resulted in an uneven FCE distributions over the entire tip region from the LE to the TE region. Under the studied tip gaps and coolant mass flow rates, the PS slot configuration provided a superior blade tip cooling performance under most operating conditions, but the SS slot configuration provided an outstanding cooling performance on blade tip only at a large amount of coolant mass flow rate compared to PS slot. Thus, the blade tip with a PS slot is recommended as a robust cooling design. However, the blade tip with a SS slot may have a limited application for design and off-design conditions.

Structured light illumination for pressure-sensitive paint measurement under ambient light

We propose a pressure-sensitive paint (PSP) method under ambient light based on structured light illumination. In the PSP method, pressure is obtained by measuring the variation of the emission light intensity from a PSP coating when it is illuminated by a light source. Since the extraction of the emission light from ambient light is difficult in the conventional PSP method, the existence of ambient light induces a noticeable measurement error. While spatially uniform light is used as illumination light in the conventional PSP method, structured light, the spatial intensity of which is actively controlled, is used in the proposed method. By measuring the PSP emission by varying the spatial pattern of the structured light illumination, one can eliminate ambient light, which is not synchronized with the structured light and can measure pressure without the effect of ambient light. In this study, we demonstrate the pressure measurement under ambient light using structured light with a sinusoidal wave generated by a digital mirror device. The measured pressure agrees well with the pressure measured by a pressure transducer connected to a pressure tap. The proposed method is promising under ambient light conditions.

계단 형상의 단차가 적용된 팬 형상 막냉각 홀 하류에서의 막냉각 효율에 관한 실험적 연구

In this study, the adiabatic film cooling effectiveness downstream of a row of the fan-shaped film cooling holes with various staircase geometries at hole exit was measured and analyzed using a pressure sensitive paint method. Experiments were conducted with baseline fan-shaped film cooling hole and the three different configurations with staircase geometry, in which ‘two-step’ geometry was applied to the hole exit and its lateral length is changed from 2.3D to 6D. A low-speed open-type wind tunnel was used for the experiments. The density ratio of the coolant fluid to main stream was 1.0 and the blowing ratio ranged between 0.5 and 2.0. The result showed that the staircase geometry promotes lateral spreading of the coolant at the hole exit, which results in better film coverage near the hole. At low blowing ratio, the film cooling effectiveness distributions are quite similar for all the tested cases except near the hole exit because the momentum of the coolant is low and baseline configuration also has good coverage downstream of the hole. However as the blowing ratio becomes higher, the effect of the staircase geometry becomes stronger and higher film cooling effectiveness values are obtained due to increased film coverage with reduced momentum of the coolant on the whole measured area.

Effects of seal installation in the mid-passage gap between turbine blade platforms on film cooling

Hot combustion gas in gas turbines can be ingested into the mid-passage gap between the blade platforms, resulting potentially a catastrophic damage. To prevent the ingress of hot gas, the blade platform underneath cavity is pressurized with purge air. Seals are typically installed in the mid-passage gap to minimize the purge air requirement. Under inadequate back flow margin, ingress of the main flow can occur especially at the upstream region of the mid-passage gap due to the pressure distribution characteristics on the platform. Excessive leakage flow can significantly reduce the turbine performance. This study investigated the effect of a seal installed in the mid-passage gap on film cooling effectiveness and heat transfer on the platform. Experiments were conducted by varying the ratio of the leakage flow to the main flow by 0.2%, 0.4%, and 0.6%, in which the mid-passage gap was unblocked (no seal; Opening 100% case) and partially blocked (seal; opening 50% case). The film cooling effectiveness of the platform was measured using the pressure sensitive paint method, and the heat/mass transfer coefficient of the platform was obtained using the naphthalene sublimation method. The seal in the mid-passage gap reduced or prevented completely the ingress of main flow under the given conditions. Under a high blowing ratio, the seal had little effect on the platform film cooling effectiveness. At the same mass flow rate of leakage flow, the heat transfer distributions were similar, regardless of whether a seal was installed. However, the platform with a partial seal in the opening 50% case showed a peak in the heat transfer closer to the gap than the platform without the seal, as the leakage flow reattached closer to the gap.

Scaling Considerations for Thermal and Pressure-Sensitive Paint Methods Used to Determine Adiabatic Effectiveness

Abstract To be representative of engine conditions, a measurement of film cooling behavior with an experiment must involve matching certain nondimensional parameters, such as freestream Reynolds number. However, the coolant flowrate must also be scaled between the experiments and engine conditions to accurately predict film cooling effectiveness. This process is complicated by gas property variation with temperature. Additionally, selection of the appropriate coolant flowrate parameter to scale from low to high temperatures is a topic of continued uncertainty. Furthermore, experiments are commonly conducted using thermal measurement techniques with infrared thermography (IR), but the use of pressure-sensitive paints (PSPs) implementing the heat-mass transfer analogy is also common. Thus, the question arises of how the adiabatic effectiveness distributions compare between mass transfer experimental methods and thermal experimental methods and whether these two methods are sensitive to coolant flowrate parameters in different ways. In this study, a thermal technique with IR was compared with a heat-mass transfer method with a PSP on a flat plate model with a 7-7-7 film cooling hole. While adiabatic effectiveness is best scaled by accounting for specific heats with the advective capacity ratio (ACR) using thermal techniques, results revealed that PSP measurements are scaled best with the mass flux ratio (M). The difference in these methods has significant implications for engine designers that rely on PSP experimental data to predict engine thermal behavior as PSP is fundamentally not sensitive to the same relevant physical mechanisms to which thermal methods are sensitive.

Film cooling characteristics on blade platform with a leakage flow through mid-passage gap

Each turbine rotor assembly is composed of several blades, and there is a mid-passage gap between blade platforms. Purge air is supplied through the mid-passage gap to prevent the ingress of hot combustion gas which could lead to thermal damage to the blade platforms. The leakage flow (coolant) egested through the mid-passage gap affects the heat transfer of the blade platform and provides a cooling to the platform. This study investigated the effects of leakage flow on film cooling effectiveness and heat transfer on the platform with a mid-passage gap. The effects of main flow ingestion through the gap on the film cooling effectiveness and heat transfer on the platform were measured for different mass flow ratios (MFRs) of the leakage flow. The film cooling effectiveness was measured using the pressure sensitive paint method, and the heat/mass transfer was measured using the naphthalene sublimation method. The measured mass flow ratios of the leakage flow to the main flow were 0.2%, 0.4%, and 0.6%. At low mass flow ratios (MFR = 0.2%, 0.4%), the main flow ingested under the upstream region of the mid-passage gap and the leakage flow egested through the downstream region of the gap. The egested leakage flow provided a high film cooling effectiveness on the suction side downstream region. However, the leakage flow was egested from the gap with an injection angle of 90° and reattached to the surface, resulting in a high heat transfer in the suction side region near the gap. At a high mass flow ratio (MFR = 0.6%), the leakage flow egested through the entire mid-passage gap, but the leakage flow penetrated into the main flow resulted in a low film cooling effectiveness. As the leakage flow interacted with the main flow and formed a vortex, this resulted a region with film cooling effectiveness decrease and heat transfer increase.

Uncertainty analysis of motion-capturing pressure-sensitive paint method based on unsteady surface-pressure measurement on fluttering airfoil

Motion-capturing pressure-sensitive paint (PSP) methods give a pressure map over an unsteady aerodynamic surface. To collect a quantitative pressure measurement using this method, unsteady analysis is important. Due to the unsteady motion of an aerodynamic surface, the luminescent output acquired by a stationary imaging device is a time-dependent value. This creates a time-dependent change in signal-to-noise ratio. An uncertainty analysis is given based on the signal-to-noise ratio of the luminescent output. Unsteady surface pressure over a high aspect-ratio (YXX) wing with 11.5% thickness ratio at 30% chord is considered for analysis. Under Mach 0.8 flow, the YXX wing flutters at 13.7 Hz with a shock oscillation over the surface. With the proposed uncertainty analysis, the overall pressure uncertainty, based off of traditional unsteady pressure taps, of the PSP measurement is given as 3.5 [%]. The measurement region that gives the high signal-to-noise ratio had uncertainty as low as 2.9 [%].

Motion-capturing pressure-sensitive paint method under transient illumination by plasma source

The motion-capturing pressure-sensitive paint (PSP) method is validated under transient illumination to capture unsteady surface pressure. It is applied to measure a wall pressure distribution in a footprint of a fluctuating oblique shock generated by near-surface electric discharge in a supersonic airflow. For a surface pressure measurement using PSP, the electric discharge adds transient illumination that overlaps with the PSP emission. By using the motion-capturing PSP method, unsteady surface pressure including the plasma-induced shock wave is captured with temporal resolution of 10 kHz. Comparison to the existing PSP method as well as uncertainty analysis are also given.

3D surface pressure measurement with single light-field camera and pressure-sensitive paint

A novel technique that simultaneously measures three-dimensional model geometry, as well as surface pressure distribution, with single camera is demonstrated in this study. The technique takes the advantage of light-field photography which can capture three-dimensional information with single light-field camera, and combines it with the intensity-based pressure-sensitive paint method. The proposed single camera light-field three-dimensional pressure measurement technique (LF-3DPSP) utilises a similar hardware setup to the traditional two-dimensional pressure measurement technique, with exception that the wind-on, wind-off and model geometry images are captured via an in-house-constructed light-field camera. The proposed LF-3DPSP technique was validated with a Mach 5 flared cone model test. Results show that the technique is capable of measuring three-dimensional geometry with high accuracy for relatively large curvature models, and the pressure results compare well with the Schlieren tests, analytical calculations, and numerical simulations.

Experimental Evaluation of Thermal and Mass Transfer Techniques to Measure Adiabatic Effectiveness With Various Coolant to Freestream Property Ratios

Experimentally evaluating gas turbine cooling schemes is generally prohibitive at engine conditions. Thus, researchers conduct film cooling experiments near room temperature and attempt to scale the results to engine conditions. An increasingly popular method of evaluating adiabatic effectiveness employs pressure sensitive paint (PSP) and the heat–mass transfer analogy. The suitability of mass transfer methods as a substitute for thermal methods is of interest in the present work. Much scaling work has been dedicated to the influence of the coolant-to-freestream density ratio (DR), but other fluid properties also differ between experimental and engine conditions. Most notably in the context of an examination of the ability of PSP to serve as a proxy for thermal methods are the properties that directly influence thermal transport. That is, even with an adiabatic wall, there is still heat transfer between the freestream flow and the coolant plume, and the mass transfer analogy would not be expected to account for the specific heat or thermal conductivity distributions within the flow. Using various coolant gases (air, carbon dioxide, nitrogen, and argon) and comparing with thermal experiments, the efficacy of the PSP method as a direct substitute for thermal measurements was evaluated on a cylindrical leading edge model with compound coolant injection. The results thus allow examination of how the two methods respond to different property variations. Overall, the PSP technique was found to overpredict the adiabatic effectiveness when compared to the results obtained from infrared (IR) thermography, but still reveals valuable information regarding the coolant flow.

Measuring System for Pressure Sensitive Paint (PSP) Calibration in the Range of Low Pressure Gains

The measurement by means of the PSP method in the range of low pressure gains (up to ±30kPa) may constitute a supplement to the low-pressure compressor stage research methods (pitot tubes, thermal anemometry, LDA). This paper presents an in-house PSP calibration system implemented in the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology. The tests were carried out using a calibration chamber co-operating with a measuring system controlled by an original handler operating in the LabView environment. The pressure-dependent luminous intensity of recorded light was determined at different values of temperature and levels of excitation illumination. The system makes it possible to calibrate pressure sensitive paints and perform measurements in the range of pressure values occurring in the systems of industrial fans.

モーションキャプチャーPSP法と非定常流体計測への適用

モーションキャプチャーPSP法と非定常流体計測への適用

A motion-capturing pressure-sensitive paint method

A motion-capturing pressure-sensitive paint (PSP) method is introduced to capture unsteady motions and flow fields of objects. Conventionally, the intensity-based method has been used to cancel the pressure-independent image of a PSP measurement to extract the pressure-dependent image. However, this method is not applicable if the pressure-independent image changes in time. The new motion-capturing method, namely imaging a two-color PSP-coated surface with a high-speed color camera, acquires both images simultaneously. This PSP has a reference luminescence in blue established using an appropriately tuned quantum dot, and a pressure-sensitive luminescence in red from bathophen ruthenium. The former has a luminescence spectrum from 400 to 550 nm, whereas the spectrum of the latter is around 620 nm. These are matched with the blue and red color ranges of the camera, which simultaneously acquires these images. By simply ratioing the blue and red images from each measurement, we can cancel the pressure-independent image, which are dependent on camera-PSP distance and illumination non-uniformity. The pressure sensitivity of the motion-capturing method is 1.12%/kPa which, due to the spectral overlap of the red and blue images, is slightly smaller than that of the intensity-based method by 0.01%/kPa. The response times are almost identical for both methods as both can respond to a step-pressure change within a time delay of 90 μs. A demonstration of this new method to sonic-jet impingement shows that the pressure-independent images can be used to cancel that component of the flow during unsteady motion and flows over a PSP-coated surface. The method can provide real-time pressure maps during unsteady motion created during a sonic jet impingement.

TURBINE BLADE FILM COOLING USING PSP TECHNIQUE

Film cooling is widely used to protect modern gas turbine blades and vanes from the ever increasing inlet temperatures. Film cooling involves a very complex turbulent flow-field, the characterization of which is necessary for reliable and economical design. Several experimental studies have focused on gas turbine blade, vane and end-wall film cooling over the past few decades. Measurements of heat transfer coefficients, film cooling effectiveness values and heat flux ratios using several different experimental methods have been reported. The emphasis of this current review is on the Pressure Sensitive Paint (PSP) mass transfer analogy to determine the film cooling effectiveness. The theoretical basis of the method is presented in detail. Important results in the open literature obtained using the PSP method are presented, discussing parametric effects of blowing ratio, momentum ratio, density ratio, hole shape, surface geometry, free-stream turbulence on flat plates, turbine blades, vanes and end-walls. The PSP method provides very high resolution contours of film cooling effectiveness, without being subject to the conduction error in high thermal gradient regions near the hole.

Measurement of Flow Properties and Thrust on Scramjet Nozzle Using Pressure-Sensitive Paint

An experimental study of flows over a single expansion ramp nozzle with flush-mounted side walls was carried out at the DLR, German Aerospace Center. The tests were performed at a freestream Mach number of 7 in the hypersonic wind tunnel H2K in Cologne. The Reynolds number and nozzle pressure ratios in the wind-tunnel flow were varied to study the performance of the scramjet nozzle at different flight altitudes and run conditions. The static pressure distribution on the single expansion ramp was measured by both the pressure-sensitive paint method and by using pressure transducer taps located at discrete points on the surface. These two methods showed that the nozzle pressure ratio and the freestream Reynolds number do not substantially influence the static pressure ratio on the expansion ramp. A pitot rake was also used to measure the pressure distribution in the nozzle wake. Using this technique the nozzle flow in the wake could be visualized and the strong influence of the nozzle pressure ratio on the interaction between nozzle and external flows was revealed. The data obtained by the different measurement techniques permitted a characterization of the nozzle flow and gave insight into the properties of single expansion ramp nozzle flows. The thrust generated by the nozzle, the thrust efficiency coefficient, and the thrust vector angle were calculated by using the pressure data obtained by both pressure measurement techniques and the results compared. It was shown that thrust values obtained from pressure tap measurements were overestimated. Criteria were developed to aid in the design and optimization of the thrust-related performance criteria for this single ramp nozzle.

Experimental Study of a Scramjet Nozzle Flow Using the Pressure-Sensitive-Paint Method

An experimental study on scramjet nozzle flows was carried out at the German Aerospace Center. The tests were performed at a free-stream Mach number of 7 in the hypersonic wind tunnel H2K in Cologne. The Reynolds number in the tunnel flow was varied in order to study the performance of the scramjet nozzle at different flight altitudes. The effects of different nozzle pressure ratios were investigated and compared. The static pressure distribution on the single expansion ramp was measured by both the Pressure-Sensitive Paint (PSP) Method and PSI pressure transducers. The PSP method enables one to gain detailed field information about the pressure distribution on the entire nozzle surface. A Pitot rake was used to measure the Pitot pressure distribution in the nozzle wake. The data obtained by the different measurement techniques permitted a characterization of the nozzle flow and gave an insight into the properties of scramjet nozzle flows.

B208 低レイノルズ数におけるキャンバー翼空力測定に向けた圧力分布計測法の開発

For a surface pressure measurement in wind tunnel, following techniques are used: a differential pressure meter, and the pressure-sensitive paint method. The former one can measure the pressure with high-precision, but the measurement cost is expensive. The latter one can reduce the cost; however, the change in the oxygen-partial-pressure becomes small at low-speed. In the author's previous study, a new pressure measurement method has been proposed. The method uses a laser displacement sensor. The surface pressures are obtained by measuring the deflection of a film which is attached on the surface of the model. The verification experiment using a high precision sensor, whose reference length from the sensor head to the target is 30mm, demonstrates reasonable results. In this paper, a middle precision sensor, whose reference length is 150mm, is also introduced. The measurement accuracy of the pressure measured by two different sensors is demonstrated.