C114 PSPによる非定常表面圧力分布計測

The videogrammetric model deformation (VMD) measurement technique is developed, which is integrated with fast-responding pressure sensitive paint (PSP) to measure simultaneously unsteady aeroelastic deformation and pressure field of a wing in transonic and supersonic wind tunnels. The measurement system and data processing are described. The method of generating a deformed wing surface based on VMD measurements for PSP data mapping on the surface is developed and evaluated through simulation. Simultaneous VMD and PSP measurements on an oscillating airfoil section have been conducted in a transonic wind tunnel, and VMD data are obtained from the registration targets in PSP images. Furthermore, dynamic aeroelastic deformation of a thin flexible rectangular wing is measured by using a single-camera VMD system in a low-speed wind tunnel, and the vibration modes are extracted at different angles of attack and freestream velocities.

A first time-resolved pressure-sensitive paint (PSP) test campaign at the European Transonic Wind Tunnel (ETW) was conducted within the research initiative “Unsteady flow and interaction phenomena at High Speed Stall conditions”. One of the objectives of this wind tunnel campaign was to resolve time-series of surface pressure distributions caused by complex 3-D buffet phenomena on a full-span airplane model XRF-1 transport aircraft configuration. At higher angle-of-attack and high Mach number, pressure fluctuations with a frequency of several hundred Hertz are expected to occur on the main wing and the horizontal tail plane (HTP) caused by the buffet effect. To capture the expected buffet phenomena by PSP, the German Aerospace Center developed a time-resolved PSP measurement and data acquisition system as well as a post-processing method for measurements in ETW. The measurements were conducted on the main wing and HTP simultaneously, with a camera frame rate of up to 2 kHz. The transonic buffet phenomena were observed at the flight relevant Reynolds number Re = 12.9 × 106 and Re = 25.0 × 106. The time-varying surface pressure distribution on the model was successfully captured by PSP. The time-series and spectra of both PSP and pressure transducer data match very well.

As an application of visible light communication (VLC), visible light positioning (VLP) technology has great potential for vehicle positioning due to its characteristics of no electromagnetic interference, low cost, and high positioning accuracy. In addition, the light emitting diode (LED) in street lights, traffic lights and vehicle lighting systems makes this positioning solution attractive for vehicular applications. However, the modulated LED signal will bring blooming effects on the images captured by a complementary metal oxide semiconductor (CMOS) camera. And it will decrease the positioning performance. Meanwhile, positioning errors will happen when the CMOS camera is tilted. In the paper, a vehicle positioning scheme based on VLC is proposed and experimentally demonstrated. It uses LED street light as a transmitter and the CMOS camera as a receiver. To mitigate the blooming effect in the CMOS camera based VLC, a bit length estimation (BLE) based sampling scheme is proposed to obtain the reference location information from the captured images. In addition, a novel angle compensation scheme combined with a particle filter is proposed to improve the accuracy of vehicle positioning when the CMOS camera is tilted. The experiments are performed under moving speeds of 40 to 80 cm/s and the measured distances of 80 to 115 cm. Assuming the performance of the proposed demonstrator is not modified when upscaling its size to a real scenario (such as speeds of 4 to 8 m/s and distances between the LED and camera of several meters), it can be concluded that as the speed of the moving vehicle is 8 m/s, the proposed vehicle positioning scheme based on VLC can achieve positioning accuracy of 0.128 m and 0.13 m for the tilt angles of 9° and 15.5°, respectively.

The fast response Pressure Sensitive Paint (PSP) was studied to develop the capability of making global pressure measurements in unsteady and short duration flow conditions. In this work, the response times of porous PSP were characterized from two dynamic calibration device. Visualization and measurements of aerodynamic effects on a Cylinder/flat plate configuration were conducted in a hypersonic wind tunnel of CAAA using the fast response PSP technique. Unsteady PSP measurement results of Ma=5 were described in this paper. PSP was sprayed on the flat plate surface and it was illuminated by a high power UV light. The luminescence was measured by a high-speed camera. After image processing, the time series absolute pressure distributions on the surface were obtained. Comparison between the PSP result and pressure transducers were also described.

Polymer/ceramic pressure-sensitive paints with reduced surface roughness were developed for measuring unsteady pressure fields in transonic flow. Four types of polymer/ceramic pressure-sensitive paints, each having different properties (such as particle size, mass content, and solvent), were formulated and applied to transonic wind-tunnel tests of a supercritical airfoil. The effects of surface roughness on the unsteady transonic flow on the airfoil were evaluated at Mach 0.74 at a Reynolds number of . It was found that all four polymer/ceramic pressure-sensitive paints could be used to measure time-series pressure distributions, but the location of the shock wave and the root-mean-square pressure fluctuations differed, depending on the type of polymer/ceramic pressure-sensitive paint. Among the tested polymer/ceramic pressure-sensitive paints, having an arithmetic surface roughness of and a cutoff frequency of 3 kHz yielded practically the same data as a clean airfoil. Using this polymer/ceramic pressure-sensitive paint, propagation of pressure waves and oscillation of shock waves on the airfoil were clearly captured. A spectral analysis revealed that the fundamental frequency of shock-wave oscillation agreed very well with that calculated based on the mechanism proposed in previous studies. These results showed that the selected polymer/ceramic pressure-sensitive paint is an effective means by which to study transonic buffeting on airfoils and three-dimensional wings.

A digital speckle pattern interferometer based on a complementary metal-oxide semiconductor (CMOS) camera is described. The temporal evolution of dynamic deformation is measured using interframe phase stepping. The flexibility of the CMOS detector is used to identify regions of interest with full-field time-averaged measurements and then to interrogate those regions with time-resolved measurements sampled at up to 70 kHz. A numerical and analytical investigation shows that the maximum surface velocity that can be reliably measured with interframe phase stepping corresponds to +/-0.3 times the surface velocity at which the interferogram is sampled at the Nyquist limit.

For many years, X-ray movies have been considered a promising tool for exploring and providing insights into chemical reactions. A simultaneous multi-element X-ray movie can further clarify the behavior difference of various elements and help investigate their interactions. The present short communication illustrates how to conduct multi-element X-ray movie imaging in a synchrotron facility solely by placing a micro-pinhole in front of a visible-light complementary metal-oxide semiconductor (CMOS) camera. It has been found that the CMOS camera can resolve X-ray fluorescence spectra when it is specially operated. In this work, a spatial resolution of ∼15 µm was achieved. In the X-ray movie, a movie frame acquisition time of 2 min and a spatial resolution of ∼50 µm were simultaneously achieved. It is clear that the CMOS camera can be a cost-efficient option for many researchers who wish to establish their own setup for visualizing chemical diffusion in various reactions.

Image measurement using pressure-sensitive paint (PSP) is an effective tool for analyzing the unsteady pressure field on the surface of a body in a low-speed air flow, which is associated with wind noise. In this study, the surface pressure fluctuation due to the tonal trailing edge (TE) noise for a two-dimensional NACA 0012 airfoil was quantitatively detected using a porous anodized aluminum PSP (AA-PSP). The emission from the PSP upon illumination by a blue laser diode was captured using a 12-bit high-speed complementary metal-oxide-semiconductor (CMOS) camera. The intensities of the captured images were converted to pressures using a standard intensity-based method. Three image-processing methods based on the fast Fourier transform (FFT) were tested to determine their efficiency in improving the signal-to-noise ratio (SNR) of the unsteady PSP data. In addition to two fundamental FFT techniques (the full data and ensemble averaging FFTs), a technique using the coherent output power (COP), which involves the cross correlation between the PSP data and the signal measured using a pointwise sound-level meter, was tested. Preliminary tests indicated that random photon shot noise dominates the intensity fluctuations in the captured PSP emissions above 200 Hz. Pressure fluctuations associated with the TE noise, whose dominant frequency is approximately 940 Hz, were successfully measured by analyzing 40,960 sequential PSP images recorded at 10 kfps. Quantitative validation using the power spectrum indicates that the COP technique is the most effective method of identification of the pressure fluctuation directly related to TE noise. It is possible to distinguish power differences with a resolution of 10 Pa $$^2$$ (4 Pa in amplitude) when the COP was employed without use of another wind-off data. This resolution cannot be achieved by the ensemble averaging FFT because of an insufficient elimination of the background noise.

The current work focuses on the development and application of fast-responding polymer/ceramic pressure-sensitive paint (PSP) as an advanced surface pressure measurement technique for unsteady flow fields in large-scale wind tunnels. To demonstrate the unsteady PSP technique, the unsteady surface pressure distribution over a hemispherical dome placed in the United States Air Force Research Laboratory’s Trisonic Gasdynamics Facility (TGF) was studied by phase-locking to the characteristic frequency in the flow caused by an unsteady separated shear layer shed from the dome. The wind tunnel was operated at stagnation pressures of 23.92 and 71.84 kPa, with the test section flow at Mach 0.6. Under the two operating conditions, the predominant shear layer frequency was measured to be 272 and 400 Hz, respectively. The quasi-periodic shear layer frequency enabled a phase-averaged method to be employed for capturing the unsteady shock motion on the hemisphere. Unsteady pressure data resulting from this technique are shown to correlate well with measurements acquired by conventional measurement techniques. Measurement uncertainty in the phase-averaging technique will be discussed. To address measurement uncertainties from temperature sensitivity and model movement, a new implementation of an AC-coupled data representation is offered.

Pressure-sensitive paint measurements for microscale supersonic flow with wedge models

Surface pressure measurements were taken on a hemisphere-on-cylinder turret in a wind tunnel using pressure sensitive paint and fast response pressure transducers. Four different turret protrusion distances were tested to study the characteristics of the unsteady pressure field on the backside and wake of the turret. Proper orthogonal decomposition was used to identify the dominant spatial surface pressure modes acting on the turret in this parametric study. It was found that the further the turret protruded into the freestream flow, the more the surface pressure field became dominated by spanwise antisymmetric surface pressure distributions resulting from anti-symmetrical vortex shedding at a normalized frequency of approximately StD=0.2. For the case of the partial hemisphere, this anti-symmetrical vortex shedding was essentially absent, insinuating that at some protrusion distance, the surface pressure environment on the turret fundamentally changes. The normalized net force rms was calculated on the turret for each configuration. It was found that the greater the turret protrusion, the greater the net force acting in the spanwise direction.

The visualization and measurements of aerodynamic effects on a 3D aircraft model were conducted using an optical pressure measurement system, based on the pressure-sensitive paint (PSP) technique. PSP technology provides a good understanding of the flow around the wind tunnel model. The PSP technique can be used to carry out absolute pressure measurements on a surface of the model and to determine additional aerodynamic data using scientific-grade cameras and image processing techniques. Surface pressures from the top, bottom, left, and right viewing directions were obtained using the DLR-PSP system on the entire surface, which can be observed by eight CCD cameras. Finally, the measured pressures can be integrated to calculate the forces and moments of the complete model, or parts thereof.

Discussion on measurement mechanism of pressure-sensitive paints

Porous pressure-sensitive paint (PSP) is employed as a visualization technique for unsteady flow features on a low-pressure turbine blade. Recognizing that the measurement of high-frequency pressure fluctuations in unsteady flows—especially in turbomachinery—has proven to be difficult, recent advancements in the development of porous PSP have enabled the high-resolution measurement of pressure fields with frequency content of at least 20 kHz. In this work, PSP is applied to an L1A low-pressure turbine blade section (Re = 20,000 based on axial chord) to visualize the surface dynamics of a vortex generator jet (VGJ) pulsed at 10.6 Hz with nitrogen gas. Intensity-based, time-resolved PSP measurements reveal the development and the surface structure of the VGJ as well as the spanwise variation in the blowing profile.Graphical Abstract[IMAGE]

<div class="section abstract"><div class="htmlview paragraph">The desire to provide integrated surface pressures for aerodynamic loads measurements has been a driving force behind the development of pressure-sensitive paint (PSP). To demonstrate the suitability of PSP for this purpose, it is not sufficient to simply show that PSP is accurate as compared to pressure taps. PSP errors due to misregistration or temperature sensitivity may be high near model edges, where pressure taps are rarely installed. Thus, PSP results will appear good compared to the taps, but will yield inaccurate results when integrated. A more stringent technique is to compare integrated PSP data over the entire model surface with balance and/or CFD results. This paper describes a simple integration method for PSP data and presents comparisons of balance and PSP results for three experiments. PSP is shown quite accurate for normal force measurements, but less effective at determining axial force and moments.</div></div>