水下粒子成像测速系统(Under Water PIV)

In January 2004, Memorial University purchased a stereoscopic Particle Image Velocimetry (PIV) system for making flow measurements. Although the system was potentially very versatile, its primary application was envisioned to be in a towing tank. The system was supplied as a complete package of hardware and software for calibration, data collection and analysis. The intention of the PIV system designers was to collect as many data frames as possible for a fixed measurement plane location, relative to the model. This required the PIV system to be fixed on the towing carriage, moving with the model being studied. It was found during some preliminary experiments that an active seeding delivery system was necessary to ensure sufficiently high seeding particle concentration, especially when measuring flow velocities around a model hull with a large yaw angle. This paper describes the development of a seeding technique for a PIV system that can be used in a towing tank. The paper also includes an estimate of the uncertainty of the measurement system, including the analysis of the flow behind the device used to deliver seed particles into the flow.

As part of the FARWAKE project, subtask 2.1.1, wake vortex flow experiments are performed using the PIV measurement technique in a water tank. The wake generating model consists of a simple wing/flap model that can be equipped with water jets to simulate propulsion effects. The model was tested at a speed of 3m/s and two angles of attack: 0and 6. Chord Reynolds number of approximately 225.000 and Vortex Reynolds numbers of approximately 150.000 and 220.000 were obtained during the tests. The main objective of the present study is to investigate the influence of a jet on the flap end vortex and the wake vortex formation. The investigation focuses on the direct influence of the jet on the flap end vortex and the (merged) vortex characteristics in the near to mid field. The main vortex characteristics addressed in this report are: the vortex trajectory, the maximum tangential velocity, the peak vorticity and the vortex core radius. The vortex information is obtained from Stereo-PIV experiments performed in a fixed plane perpendicular to the towing direction. The measurements return the 3 components of the velocity in that plane and the streamwise component of the wake vorticity. A submergible moving camera system is used in order to keep the moving vortex in the field of view during the vortex downward motion.

Memorial University purchased a Particle Image Velocimetry (PIV) system in January 2004. So far it has been used to study flow around a small propeller and a tug hull. Studies have also been made to determine the best seeding particles and the best method of introducing the seeding particles into the flow. This report describes the major components of the PIV system, and the analysis software. Some studies on the selection of seeding particles were made and they are described in this report. The PIV system was used to measure the flow field around a small model propeller and a model of a tug. The results of these experiments are also described. Finally, some recommendations are made for improving the experiment procedures and analysis techniques for future experiments.

In this report we present the methodology we are using in the AMI group to compare optic flow estimation methods in the context of the FLUID Specific Targeted Research Project - Contract No 513633 founded by the CEE. The main goal of this report is to try to unify comparison criteria between the different parnerts in order to share information and conclusions. We think that it is one of the topics we have to address in Las Palmas Meeting December next. In order to describe the methodology we use, we divide it in five steps: 1. We choose a number of optic flow estimation methods 2. We choose an image sequence dataset to apply the methods. 3. We apply the methods and we store the results in a ASCII file using an standard format 4. We define a number of statistics to compare the methods (we use the ASCII files as basic information to compare). 5. We compute the statistics for each pair of methods and we generate tables with the information. To help result interpretation we use arrow images and in the case we know the optic flow groundtruth we generate image to provide the information about what method perform better in the different areas of the image. To illustrate this approach and to fit ideas we present the results of this approach in a particular image sequence provided by LaVision in sections from 1.1 to 1.4. Then, in section 2 we remark some of the difficulties we have found in our work, which should be discussed in order to be able to compare results provided by all the partners of the FLUID project.

PIV systems rely on a combination of seed particles, laser light intensity, and camera positioning to collected velocity data. Careful attention is needed when selecting the ap- propriate setup conguration for PIV systems. This paper focuses on several areas for improvement in PIV data collection for a compressible turbulent boundary layer study on a at plate using MVG's. The topics include determining the seed particle surface preparation for a at plate, and PIV system conguration.