Experimental Investigation Of The Characteristics Of Flow Structures In Round Turbulent Impinging Streams

Turbulent impinging streams has a wide applications in the industry, it has attractedmore and more attention of investigators. The turbulent impinging stream flow is verycomplex, many studies focus on the statistical regularity about engineering practice,however the research about the fundamental characteristics of impinging streams are veryfew. An experimental study on characteristics of flow structures in round turbulentimpinging streams by using particle image velocimetry(PIV) has been introduced in thispaper.In the first of this paper, a small experimental setup of impinging stream has beendesigned and constructed, according to some experimental researchs in recent years. Theturbulent round jets, impinging jet and impinging stream with different Reynolds numberRe=2930,5850,9820,14600and nozzle spacing L/d=5,12,20are experimentallymeasured with PIV.Deal with the instantaneous velocity field of the three flows experimental data, wegain the distribution characteristics about some turbulence statistics, such as averagevelocity, fluctuation velocity, shear stress, vortex, turbulent kinetic energy and dissipationrate. Comparison of different experimental conditions, we has drew some importantconclusions about the effect of the statistics by Reynolds number and nozzle spacing.Apply the proper orthogonal decomposition (POD) method to analysis the structure ofround jet, and combine the critical-point theory to identification vortex structure. Then a setof perfect flow structure analysis method was established.By the end of this paper, using the POD method to analysis the structure of impingingstreams. The results show that: With increases Reynolds number, the structure of impingingstreams has changed from symmetrical distribution of vortex pair structure to alternatingvortices structure. The decrease of nozzle space, will cause the change-Reynolds numberincrease. Based on the reconstruction of instantaneous fluctuation velocity field and thestatistical analysis of the stagnation point position, the oscillation phenomena of impingingsurface is explained reasonably from the mesoscopic scale.