Experimental Study On The Breakup Of Power-law Liquid Sheet Formed By Two Impinging Jets

The breakup mechanism of the liquid jet is a classical fluid mechanics problem,also it has guiding significance for technical application. The liquid sheet formed byimpinging jets has been widely used in the combustion system of liquid rocket engine,for its simple construction, good atomization, low cost and high reliability. Power-lawfluid is a new kind of propellant possessing the advantages of the solid and liquidpropellant. In order to control the jet breakup and optimize the combustion progress,this paper studies the breakup progress and characteristic of the liquid sheet formedby the impinging jets.An optical test system was designed and built, including the liquid pressured andtransporting system, impinging liquid sheet system, pulse control system, High-speedimaging system, phase Doppler analyzer and waste recovery system. The opticalshadow picture can be obtained by using the High-speed camera, from which thebreakup regime and the breakup characteristic (like the breakup length, surface wavelength, spray cone angle and sheet characteristic) was extracted. By using the phaseDoppler analyzer, the3-D velocity of droplet and particle size and distribution weremeasured.Results indicate that the species of breakup regime are different with usingdifferent Power-law fluids. The sheet length-width ratio and the max length-maxwidth increase with increasing the viscosity. Thickness of the sheet edge is similar tothe jet diameter. When increasing the jet velocity, the surface wave length decreasesand the spray cone angle increases gradually and tends to the maximum angle lessthan the impinging angle. The transformation law of the breakup length is related tothe rheological behavior, when increasing the jet velocity,0.15wt%and0.25wt%Power-law fluids show twin peaks pattern, while0.35wt%and0.5wt%Power-lawfluid is single peak. Once entering the turbulent flow, the breakup length decreaseswith increasing the jet velocity. When increasing the injection pressure, the axialvelocity increases and submits symmetrical distribution along the X-axis. The radialvelocity U of the water droplets submits less symmetrical distribution compared withthe axial velocity, while disappears for Power-law fluid. The radial velocity V is nearzero. Under the same injection pressure, axial velocity decrease downstream and theattenuation rate also reduced, and radial velocity U decrease downstream withreduced symmetry. U, W and SMD reduce with increasing impinging angle. SMD decreases with increasing the injection pressure. Under the same injection pressure,SMD shows increased tendency towards the two sides of the X-axis, and change littledownstream. When the jet velocity is large enough, the SMD/D converges to0.13forwater, but0.18for0.35wt%power-law fluid. The size distribution fits very well withthe Rosin-Rammler function, Rosin diameter X0reduced with increased injectionpressure, while X0will not decreases once entering the completely developmentregime and X0/SMD=1.3~1.5for both water and Power-law fluid. Finally，evennessindex q is not linear variation with changing the injection pressure and radial position.