Hybrid pulse-burst/cross-correlation Doppler global velocimetry for high-speed velocity measurements at 100 kHz

OH-PLIF measurements were conducted for investigating the fundamental study of premixed combustion and flame characteristics. High-speed OH-PLIF measurements in premixed combustion and flame fields to image flow and composition fields in flames are quickly evolving and measurements of velocity and reactive species were recently reported in various flow configurations. The purpose of this paper is to discuss the most recent and significant advancement of technology in high-speed OH-PLIF measurements for the fundamental study of premixed combustion and flame. The highlight of this review will be focusing on explaining the concept of OH-PLIF process, its current related research, influences of process parameters, advantages and challenges pertaining to the fundamental study of combustion and flame. The results show that gas-phase combustion is significantly suppressed due to the depletion of the reactants rather than the radical adsorption. The vorticity is generated particularly close to the reaction zone where axial strain and dilatation exhibit local minima. The recommendations on future scientific studies are proposed for this novel process to move forward and to complement existing study of combustion and flame with a more sustainable approach.

Model-based review of Doppler global velocimetry techniques with laser frequency modulation

Engine processes require fundamental knowledge on specific fuel–air mixtures to reduce pollutant emissions, i.e., soot formation, $$\hbox {CO}_2$$ , and $$\hbox {NO}_{x}$$ generation, and to improve engine efficiency. However, the in-cylinder flow field of combustion engines is characterized by time-dependent and highly three-dimensional large-scale flow structures and cycle-to-cycle variations (CCV). This means that high-speed volumetric velocity measurements are required to investigate three-dimensional large-scale flow structures and CCV inside the combustion chamber at high temporal resolution. Since such data are hardly available in the literature, a high-speed tomographic particle image velocimetry (HS-TPIV) setup is used to measure the velocity field in an internal combustion engine at an engine speed of 1500 rpm and at a temporal resolution of $$10\,^\circ$$ crank angle in a maximum measurement volume of $$50\times 8\times 83\,\hbox {mm}^3$$ . To assess the quality and the validity of the high-speed volumetric measurements, the HS-TPIV results are validated using high-speed stereoscopic particle image velocimetry measurements in the engines tumble plane. To further verify the measurement quality, an extensive error estimate is conducted. Finally, the instantaneous, three-dimensional measurement results are used to analyze the impact of fluctuations due to turbulence and CCV on the flow field in several instantaneous engine cycles at several predefined crank angles. The investigation shows the three-dimensional extent of flow fluctuations inside combustion engines and qualitatively quantifies the effect of CCV in in-cylinder flow.

Doppler Global Velocimetry (DGV) is a full-field optical technique for the measurement of fluid flow velocities. The flow is illuminated using a light sheet, and the Doppler shift imposed on light scattered from moving particles within the sheet is imaged through a cell containing iodine vapor onto a solid-state array camera, thereby converting the Doppler frequency shifts into intensity variations in the image. In this paper, a DGV system is presented based around an argon-ion laser source and a fast digital image-processing system, which allows the DGV velocity map to be updated at camera frame rate. Interpretation of DGV images is complicated by errors which arise at positions some way out in the field of view due to the modified illumination and viewing vectors corresponding to these positions. Typical magnitudes of such errors are calculated. Significant errors can arise for points more than about 5 degree(s) out from the center of the field of view, and for divergence angles of the illumination beam exceeding about 10 degree(s) at a distance of 5 cm from the beam axis. Other considerations affecting system accuracy are also discussed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Doppler Global Velocimetry (DGV) is a new laser-based diagnostic which complements existing measurement capabilities for wind tunnel applications. Measurements of velocity are based on determining the Doppler shift of single frequency laser light scattered off particles in the flow field. This technique is capable of making simultaneous measurements over an entire laser sheet. This paper presents results obtained with the DGV instrument in both calibration and wind tunnel test setups. Characterization and analysis of isystem accuracy is addressed with the calibration setups. Example applications of the DGV technique for measurements on a wind tunnel model are also presented.

High-speed measurements, particularly close to the velocity of light, have always been a great challenge in the field of experimental measurement. Although traditional high-speed measurement methods based on imaging technology can achieve millions of frames per second, they face the problem that the field of view decreases with an increase in the frame rate, which is difficult to overcome in a short period. In this study, a closed multi-exposure optical path is designed first based on a 600 ps pulse laser that realizes the continuous measurement of sub-light velocity and is not subject to the field of view. The path can also be adjusted with respect to time, accurate up to sub-nanoseconds. Second, it is found that the accuracy and resolution of the present method are related to the used pulse laser and camera. Once the performances of the pulse laser and the camera are improved, the corresponding range of measurement of the velocity can be improved further. Compared with traditional pumping technologies, the proposed technology achieves continuous velocity measurement with the utilization rate of laser energy as high as 100%. Finally, we use this novel optical system to determine the flux avalanche velocity of the YBa2Cu3O7-x superconducting thin film, and a highest speed of 323.5 Km/s is obtained.

A combined Doppler Global Velocimetry (DGV) and Projection Moire Interferometry (PMI) investigation of a helicopter rotor wake flow field and rotor blade deformation is presented. The three-component DGV system uses a single-frequency, frequency-doubled Nd:YAG Laser to obtain instantaneous velocity measurements in the flow. The PMI system uses a pulsed laser-diode bar to obtain blade bending and twist measurements at the same instant that DGV measured the flow. The application of pulse lasers to DGV and PMI in large-scale wind tunnel applications represents a major step forward in the development of these technologies. As such, a great deal was learned about the difficulties of using these instruments to obtain instantaneous measurements in large facilities. Laser speckle and other image noise in the DGV data images were found to be traceable to the Nd:YAG laser. Although image processing techniques were used to virtually eliminate laser speckle noise, the source of low-frequency image noise is still under investigation. The PMI results agreed well with theoretical predictions of blade bending and twist.

The ability to scale the field of view for velocimetry methods is particularly attractive for aeroacoustics studies, where turbulence contributions in long-lived, low wavenumber structures account for the most important sources of radiated noise. Thanks to its core operating principles, Doppler global velocimetry (DGV) offers interesting opportunities for large-scale flow measurements. As is well known, a larger field-of-view (FOV) in the measurement will change the spatial resolution, meaning that each measurement is integrated across a larger control volume. This finite size will affect the velocity and turbulence measurements, as well as the observable wavenumbers in the measurement. The present study confirms the viability of DGV for studying low wavenumbers while examining the influence on higher wavenumbers of the less coherent turbulent structures also present in high-speed flows. In the flows examined by the current work, mean velocity bias error due to integration over the measurement region was shown to be small, less than 0.005%, for control volume heights up to 4 mm. Although significant energy attenuation occurs for high wavenumbers, the low wavenumber turbulent structures which dominate far-field noise are found to be unaffected by the size of the control volume required for large measurement of both laboratory- and full-scale supersonic jet flows. The results indicate a large-scale velocimetry system such as DGV can be a valuable tool for researchers to study aeroacoustics in high-speed flows.

Forty tournament-level tennis players with expert serve technique volunteered to have their serve evaluated to determine relationships between anthropometric data, extremity strength, and functional serve velocity. All players underwent a complete physical examination, a video taped serve analysis, a radar measurement of serve velocity, and a series of upper extremity strength measurements. Statistical analysis was performed to determine which factors were related to serve velocity. Statistically significant relationships were found between serve velocity and several flexibility measurements including increased dominant wrist flexion (P < 0.05), increased dominant shoulder flexion (P < 0.05), and increased dominant shoulder internal rotation at 0 degrees of abduction (P < 0.05). Several strength measurements were also related to serve velocity including elbow extension torque production (P < 0.01) and the ratios of internal to external rotational torque production for both low- and high-speed measurements (P < 0.01 concentrically and P < 0.05 eccentrically). These findings relate strength and flexibility to serve velocity, suggesting that it may be possible to increase a tennis player's serve velocity through specifically directed muscular strengthening or stretching regimens. However, prospective studies must be undertaken to demonstrate these possibilities.

The internal turbine mechanism is a new sensor that can be used for independent velocity measurement of underwater high speed moving body. It is a meaningful study when the cavitation flow field around and trajectory changes of the high speed moving body was taken into consideration. The parameterization of turbine mechanism was done at first. Then the surrounding flow field was analyzed and the CFD simulation model was established. The cavitation tunnel experiment was done at speed of 0∼10m/s with cavitation number minimum to 0.2. On this basis, an overall analysis of the sensor characteristics was done by CFD simulation results in different situation at speed of 0∼100m/s. Compared with sensor characteristics of traditional turbine measuring mechanism, this turbine mechanism has many different sensor characteristics and a wide velocity measurement range of 5m/s∼70m/s.

: Repairs and modifications were made to a flow velocity measurement system designed to measure a planar area of unsteady three component velocities in a single realization using a velocity measurement technique referred to as Doppler Global Velocimetry (DGV). Several hardware components in the system were modified and new hardware was added. Significant improvements were made to the procedures used in acquiring DGV data as well as the procedures used in reducing the acquired DGV data. Though hardware problems were - encountered successful iodine cell calibrations were acquired and attempts were made to acquire DGV velocity data from a calibration wheel and in the wake of a 6:1 prolate spheroid. These attempts were hampered by poor performance of the Nd:YAG laser and one of the digital cameras used in this research. While the magnitudes of the velocities acquired from the calibration wheel were noticeably higher than those calculated from the angular velocity and large fluctuations were present in these reduced velocities the general trends measured by the IT DGV system matched those calculated from the angular velocity: The attempt to acquire flow field data in the wake of a 6:1 prolate spheroid model was unsuccessful due to insufficient seed particle density in the area where data were to be obtained. The results of this research indicate that while significant improvements have been made to the system, there are still some significant problems to overcome.

High-turbulence flow conditions in gas turbine combustors create a rough environment for film cooling flows. Fundamental knowledge of the interaction between main flow fluctuations and cooling jet is essential to develop more efficient cooling geometries. To gain detailed insight into the turbulent flow structures, high-speed PIV measurements have been carried out in a closed loop, thermal wind tunnel facility. Velocity fields with a temporal resolution of 6 kHz and a vector spacing of 0.5 mm have been extracted from the recorded data. Measurements have been performed for a density ratio of DR = 1.2 and momentum ratios of I = 2, I = 8 and I = 15. A Makita style active turbulence grid has been used to create a main flow turbulence intensity of Tu = 18.5% and Tu = 21.5%. Mean flow fields and dominant flow structures that are present in the time-resolved velocity fields are analyzed and discussed. Finally, results for high-turbulence main flow conditions are compared with results from low-turbulence (Tu = 1%) thermographic PIV data, carried out in previous measurements. It can be observed that low-momentum jets are highly fragile. Both small and large vortices affect the jet trajectory. Depending on the current flow situation, the jet lifts off the surface or gets pushed towards the wall. The same is true for high momentum ratios and large eddies. On the other hand, small eddies cannot significantly affect high-momentum jets. The vortex gets deflected by the jet and its intensity is reduced while interacting with the high-turbulence shear layer fluctuations. All in all, turbulence can have a positive effect on the cooling film by steering the jet trajectory towards the surface. On the other hand, however, vortices can enhance the jet detachment and thus reduce the cooling efficiency of the film.

High-speed flier velocity measurement is one of the key technologies in investigating collision sites on the surfaces of spacecraft structures impacted by high-speed space debris. We have designed and constructed an optoelectronic system to accurately determine the average velocity of a flier impacting on a spacecraft structure. The system is based on two parallel laser screens, which are crossed by the fliers before impact. This system utilizes scattered light as the start and the end signal to measure the time of flight between the two screens. A wideband optical sensor has been designed and evaluated, and an electronic circuit is used to accurately record the time of flight and calculate the velocity. Experimental results show this system is adequate to measure the velocity of a flier larger than 100 µm, in the range from 0.1 to 10 km/s, with accuracy better than 1.3%, and with low cost, simplicity, and high reliability.

Doppler global velocimetry (DGV) has already been shown to be an interesting technique capable of measuring the three components of velocity in a plane. A 1-component DGV system is currently under development at the LMFA, using a stabilized continuous wave (CW) argon ion laser for emission. The receiver features only one camera for both signal and reference images and incorporates a DEFI system to adjust the incident laser light frequency and its transmission coefficient on the iodine cell absorption line. A description of the whole system is presented and a validation with measurements of axial velocities at several positions in a round free jet is proposed.

Digital particle imaging velocimetry (DPIV) is a high resolution, high accuracy, planar velocimetry technique, which provides valuable instantaneous velocity information in aeropropulsion test facilities. DPIV is capable of providing three-component flow field measurements using a two-camera, stereo viewing configuration. Doppler global velocimetry (DGV) is another planar velocimetry technique which is also capable of providing three-component flow field measurements, but requires three detector systems that must be located at oblique angles from the measurement plane. The three-dimensional (3D) configurations of either technique require multiple (DGV) or at least large (stereo PIV) optical access ports in the facility in which the measurements are being conducted. In some test facilities, only limited optical access is available (either a single viewing window or small optical access port), which prohibits the implementation of either technique for three-component flow measurements. A hybrid measurement technique is described, called planar particle image Doppler velocimetry (PPIDV), which combines elements from both the DPIV and DGV techniques into a single detection system. The resulting system is capable of measuring all three components of velocity across a planar region of a flow field through a single optical access port. An error analysis is performed which reveals an optimal configuration for the DGV portion of the measurement system. Measurements of a rotating wheel are used to verify the integrity of the technique. Then simultaneous measurements of a nozzle flow are obtained using both a stereo viewing DPIV system and the PPIDV system.