Experimental Research On The Eccentric Taylor-Couette Flow In Small Gap

Taylor-Couette flow(TC flow),the flow in the annular gap between two coaxial co-or counter-rotating cylinders has characteristics of simple structure,easy-to-control parameters and closed-flow system,served as a paradigm for studying flow stability and turbulence theory.When an eccentric distance exsits between the axials of two cylinders,the rotating inner rotor produces hydrodynamic effect and causes circumferential pressure distribution in the eccentric annular gap.The eccentric Taylor-Couette flow is different from the coaxial Taylor-Couette flow in the resistance torque characteristics,flow regimes and cavitation et al.By comparing with the coaxial Taylor-Couette flow,the experimental research on the resistance torque characteristics,flow regimes,flow transtition and flow stability of eccentric Taylor-Couette Flow in small gap(??0.97)is carried out.By observing the pressure values at various points along the circumferential direction in the middle transversal surface of the eccentric annular gap,the law of cavitation in low-pressure region with different eccentricity and different inner rotor speeds is obtained.Obviously,the higher the rotational speed and the larger the eccentricity,the more severe the cavitation in the low-pressure region.Combined with the cut-off pressure caused by the liquid vapor pressure in the low-pressure region,the cavitation number of the fluid near the inner surface of the rotor can be used as the basis for judging cavitation.The measured cavitation pressure is used in the mass conservation method to solve the Reynolds equation.The pressure distribution simulated in the positive pressure area is in good agreement with the experimental measured value,but there is much difference between the simulation and the experiment in the low-pressure range.Through the experimental research of resistance torque characteristics on coaxial Taylor-Couette Flow in small gap,it is concluded that the dimensionless resistance torque(G)is related to the radius ratio and the Reynolds number(Re).The dimensionless resistance torques and Reynolds number are exponential law in the coaxial Taylor-Couette Flow:G:Re^a,and experimental data shows thataincreases from 1.67 to 1.82 as the Reynolds number increases.In the ultimate turbulent regime,there is a relationship of Nu??Ta^0.39.In the eccentric Taylor-Couette flow,when the Reynolds number is the same,the larger the eccentricity,the greater the dimensionless resistance torque.The increase rate of the dimensionless resistance torque relative to the coaxial gap under the eccentric gap is obtained.When Ta?3.5×10⁷,the eccentric Taylor-Couette flow enters the ultimate turbulent regime,but experimental data does not show the existence of Nu??Ta^0.39relationship.Visual experiments show that the Couette laminar flow appears first when the Reynolds number increases from zero.The Taylor vortex with light and dark lines appears at Re=382(?=0.99).As the Reynolds number increases further,the Taylor vortex turns into wave vortex at Re=425.5.When the Reynolds number reaches Re=1286.3,the light and dark stripes are no longer continuous and become independent short-wavelength burst until the short-wavelength burst reaches saturation in the flow regime,called Very Short Wavelength Bursts.Numerical simulations of the eccentric Taylor-Couette flow show that the velocity of fluid in the radial direction vary mainly in the boundary layer of the gap.The velocity of middle is relatively stable.The eccentricity has different effects on the Taylor vortex at different angles.Radius ratio,eccentricity,pressure distribution and cavitation have an influence on the stability in Taylor-Couette system.In the coaxial Taylor-Couette flow,the larger the gap and the smaller the diameter,the smaller the critical Reynolds number.When the radius ratio is the same,the critical Reynolds number is equivalent.In the eccentric Taylor-Couette flow,the greater the eccentricity,the larger the critical Reynolds number.If cavitation occurs before the critical Reynolds number,the transition point is not obvious.If cavitation occurs affer the critical Reynolds number,the transition point is not affected.