| The light-field particle image velocimetry(LFPIV)is a novel and a promising technology to extract the three-dimensional(3D)velocity of fluid by using a single light field camera.The PIV techniques used previously in the literature have following limitations:(1)complex hardware setups,(2)large space requirements,(3)processing time and(4)usage of multiple cameras.It is hypothesized that the LFPIV may be used to circumvent these limitations.In this thesis research,the LFPIV is used for the accurate measurement of the 3D velocity field in a supersonic flow.It is to test the capability of an LFPIV technique in a high-speed compressible flow for the first time.Previously,the LFPIV technique was only applied in low-speed jets and vortexes.To establish the efficacy of the proposed technique following validations are conducted:(1)qualitative validation i.e.the prominent shock cells and Mach disk results by the LFPIV are compared with the schlieren results and(2)quantitative validation i.e.the velocity profile and the Mach number distribution by the LFPIV are compared with the 2D PIV and a difference of 1% is observed in the results.In this research,the supersonic nozzle was designed by using two radii method and method of characteristics(MOC).To verify the existence of the uniform shock waves outside the supersonic nozzle a 2D computational model of the nozzle is developed by using commercially available software ANSYS.The mesh independence test was also carried out with variable mesh sizes coarse,medium and fine mesh.In the current research,three experimental setups are fabricated for qualitative and quantitative analysis purposes:(1)Schlieren based experiments,(2)2D PIV experiment with 1?m aluminium oxide particles and(3)LFPIV experiment with 0.5?m aluminium oxide particles.The experimental studies of mirror schlieren were conducted with horizontal and vertical knife edges.These results provided us with the validation of the constructed nozzle with an over-expanded,perfectly expanded and under-expanded flow outside of the nozzle respectively.The results were used to achieve the geometry of a shock structure and its cell,later used in the verification of geometry in LFPIV results and for the validation of simulation results.The experimental investigation was then carried out for the 2D PIV in a supersonic jet flow.The 2D PIV measurements provided us with the mean velocity v m/s in the y-direction and mean velocity in the x-direction from the 150 instantaneous images captured and processed.The supersonic value of mean velocity in y-direction was found to be from 0.9 Mach to 1.2 Mach.The velocities achieved were from 280m/s-384m/s including the outer jet boundary area.Lastly,the innovative and novel technique LFPIV was applied to the supersonic flow for the first time.The results achieved were from Mach 0.9 to 1.2.The velocities achieved were from 231 m/s~385 m/s including the outer jet boundary area.This Mach number and velocity ranges were validated and compared with 2D PIV.Finally,the velocity difference analysis was conducted quantitatively through probability distribution function(PDF)and cumulative distribution function(CDF).The velocity difference was found to be at 1% and difference of Mach number distribution to be at 1.2%.It is concluded that LFPIV velocities can be compared with 2DPIV quantitatively.The significance of this research work is(1)firstly,successfully validated the capability of LFPIV technique in a high speed supersonic compressible flow for the first time in the world(2)secondly,successfully constructed a supersonic nozzle to conduct Schlieren,2D and 3D PIV experiments on it(3)thirdly,employing LFPIV in a restrictive optical access system i.e.supersonic jet while using a single light field camera,(4)fourthly,achieving comparable results to other 3D PIV techniques with a simple setup(5)lastly,to have successfully compared and analysed LFPIV results qualitatively and quantitatively with schlieren and 2DPIV. |
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