Exprimental Set up


Exprimental Set up



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This image illustrates the experimental setup used to conduct this experiment. The model used is a beveled-edge disk with 0.254m diameter of the lower surface as shown in Fig.1. Two cylindrical tabs each of 1.95cm diameter were flushed with the lower surface of the disk. A 0.305x0.305x0.305m tank is used to provide for constant head and drive the desired flow through the tabs. The two tabs were connected individually to the bottom of the tank via vinyl hoses. A pump was used to feed the tank with water extracted from the downstream flow of the tunnel. The pump delivers water to the tank through a wall tab near the bottom. Inclined flaps were placed against the feeding stream to damp out most of the turbulence accompanying the feeding process. In addition, flow-straightening tubes were fixed at the outlets to the vinyl hoses to reduce any large-scale turbulence associated with the suck down by the water column below the tank. The current arrangement permits different tank elevations and adjustments of the pump output. The disk is mounted by threaded rods to a plate at the top of the tunnel in order to allow adjustment of the height of the disk with respect to the ground. The disk was placed with the jets in tandem arrangement with respect to the flow.

A 55-Watt Copper Vapor pulsing laser is used to illuminate the interrogation plane of the flow field. The peak power of the laser is 55 Watts at the nominal frequency of 10 KHz with approximately 55 mJoule/exposure. Using a set of sheet forming optics, a laser sheet that is 0.002m thick and 0.065m wide is delivered in the test section. The laser sheet plane is positioned in the plane of the jet centerlines normal to the free stream. Only this plane was considered in the present study. The field of view is adjusted to a square region of 0.065m(H) x 0.065m. The images are acquired with a digital camera (EG&G MD4256 CCD) placed normal to the plane of interest. The camera is capable of taking 1000 images/sec with a resolution of 256x256 pixels. For the current experiments the sampling frequency of the camera was set to 500fps. Both the laser and the camera are controlled and synchronized by a computer, which serves also as an image acquisition system that has an integrated frame grabber (EG&G SB4001) and an image buffer for real time data storage with a transfer rate of 80 Mbytes/sec. The frame grabber buffer memory allows storing of a sequence of 2048 frames. Florescent particles of 50 microns mean diameter were used as flow tracers



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