Study of steady and pulsating impinging jets

An experimental investigation on the fluid mechanics of steady and pulsed impinging jets is presented in this thesis. An experimental facility was custom-built in order to generate axisymmetric and incompressible impinging jets (pulsed and' steady). In order to ensure that the velocity profiles at the exit were fully developed, the jet was discharged from a round nozzle of 50 diameters in length. The effects of the Reynolds number, the nozzle-to-plate spacing and the Strouhal number were investigated systematically. The range of the Reynolds numbers covered is 4000 to 10000 for the steady jets, and 4200 to 10240 for the pulsed jets. The nozzle-to-plate spacings considered are 2, 3 and 4 nozzle diameters, because at these distances heat transfer enhancement is present for pulsed jets. The Strouhal number ranges from 0 (steady case) to 0.5. It was found that the Reynolds number does not affect the flow field of impinging jets as significantly as the nozzle-to-plate spacing, in particular, for pulsed jets, which exhibit significant changes in the distribution of the Reynolds stresses near the impinging wall for small nozzle-to-plate spacings. In addition, it was also found that the axial convection term of the mean axial momentum balance near the impinging wall is significantly larger for a jet pulsed at approximately St = 0.5 than its steady counterpart when Hid ::::: 4. This work also expands the present knowledgebase of both steady and pulsed jets in three main areas; (1) it presents in-depth velocity measurements and turbulence statistics for pulsed and steady jets, (2) the transitional regime of impinging jets is examined, and finally, (3) it presents data for turbulence model validation ofa real incompressible pulsed jet.EThOS - Electronic Theses Online ServiceGBUnited Kingdo