Research On Flow And Heat Transfer In Horizontal Tubes Under Rolling Condition

In this.paper,a horizontal circular pipe which ratio is 1:1 to experimental geometry with single-phase water as the working fluid is builded,and fully structured hexahedron grid is constructed using the ICEM software.Based on the model provided by the FLUENT platform,an external force model in a non-inertial coordinate system is constructed according to the oscillating motion of the horizontal pipe.In this way,a mathematical and physical model for single phase water flow and heat transfer in horizontal pipe under rolling motion is established.The momentum source terms are added to the momentum equation in the light of theoretical analysis.And the custom functions of rolling motion and momentum source are loaded into the FLUENT software.Three-dimensional unsteady state numerical simulations were performed on the experimental horizontal tubes under rolling motion using time-averaging two-equation k-?model,seven-equation RSM model and non-time-averaging large vortex sub-lattice models respectively.The large vortex WMLES S-Omega model is taken as the best model finally by comparing the calculation results of different models with the experimental data.Stationary and rolling conditions are studied using large eddy simulations.The distribution of the velocity in the pipe and the variation of the instantaneous velocity field under rolling motion were analyzed and compared with static condition.The formula of the friction coefficient in the pipe under rolling condition was deduced through force analysis.What's more,the pressure drop composition and the variation law of the instantaneous pressure drop in the test section under rolling motion were analyzed.The influence of rolling motion on the heat transfer characteristics was investigated using constant heat flux boundary conditions.The instantaneous temperature variation of the wall,the near wall fluid and the distribution of the average heat transfer coefficient was studied.Finally,the transient temperature of the outlet fluid under static and rolling conditions was compared.The influences of the rolling period,the rolling amplitude,the Reynolds number and the rolling radius on flow and heat transfer characteristics are mainly studied.The calculation results showed that the instantaneous frictional resistance coefficient,velocity and temperature fluctuate with time under the rolling motion.The fluctuation period of instantaneous velocity and temperature on the cross-section at the middle horizontal line which parallel to the rolling axis is half of the rolling motion period.The fluctuation period of instantaneous velocity and temperature on the cross-section at other positions are the same as the rolling period.The amplitude of instantaneous velocity and instantaneous temperature gradually decrease from the top and bottom to the middle of the cross section.When other factors are the same,as the rolling amplitude increases,the speed fluctuation amplitude,the driving pressure drop,the total pressure drop,the tangential pressure drop,the peak value and fluctuation amplitude of the centrifugal pressure drop,the peak as well as valley value and average value of the frictional resistance coefficient increases in the test position,while the instantaneous temperature,temperature fluctuation amplitude and time average temperature of the wall decrease.When other factors are the same,with the increase of the rolling period,the maximum value of the instantaneous temperature,the amplitude of the temperature change and the mean value at the top wall are increased,and the average velocity,the velocity amplitude,the variation range of driving pressure drop in the test section,tangential pressure drop,the centrifugal pressure drop,peak and valley values of the frictional resistance coefficient,as well as the average value,are reduced All other monitoring point average velocity,velocity amplitude,change range of driving pressure drop in the test section,tangential pressure drop,centrifugal pressure drop,the peak and valley value and average value of friction resistance coefficient are reduced.With the increase of the fluid Reynolds number under the rolling condition,both the amplitude value as well as the average value of the frictional resistance coefficient in the test section and the temperature of the top wall in the cross section decrease.In addition,it is also found that the larger the rolling radius,the greater the fluctuation range of the frictional resistance coefficient,and the rolling radius has almost no effect on the heat transfer in the horizontal pipe.This explains to a certain extent that the Coriolis inertial force is the main affecting factor the heat transfer in the horizontal tube under rolling motion.The secondary flow occurs in the horizontal pipeline under the rolling condition,and the secondary flow is an important factor that causes the difference characteristics of flow and heat transfer between the rolling and the stationary condition.Under ocean conditions,the rolling motion generates periodic inertial forces,and the presence of additional inertial forces causes boundary layer changes,finally inducing the changes of flow resistance and heat transfer coefficient in the horizontal circular channel.