Research On The Numerical Method To Calculate The Droplet's Drag Force And Its Application On The Steam Drier

In many nuclear power equipments,there existsgas-droplet two-phase flow.To analyse the characteristics of the two-phase flow provides instructive significance for the design of nuclear power equipments.The droplet's drag force is a key factor to research the gas-droplet two-phase flow.It is too difficult to investigate the drag force of the droplet in nuclear power equipmentsby experiments because of the condition of high pressure and temperature.Therefore,to build numerical methods to calculate the drag force is significant for the analysing of the gas-droplet two-phase flow in nuclear power equipments.Numerical methods were built to calculate the droplet's drag force.The single droplet's motion in uniform gas flow was simulated by using DNS coupling with VOF method.Control force was adopted on the droplet by the body-force source item of the momentum conservation equation to make the droplet into the steady state.Then the drag force's magnitudeequaled to the control force's magnitude,so the drag force could be computed.On the control of the droplet,it was found that the droplet's motion under PID control could diffuse.By improving the control of the droplet,two absolutely convergent methods were developed to calculate the droplet's drag force: D method,differential force was adopted on the droplet and the drag coefficient was computed by the droplet's terminal velocity;PD method,proportional-differential force was adopted on the droplet and the drag coefficient was computed by the displacement of the droplet's terminal position.By analysing the motion equations of the droplet,control parameters' adjusting method was proposed,which improved the two methods' efficiency significantly.As a result,D and PD methods applied to batch calculations.To validate the above numerical methods,the visual validation experiments were designed and carried out,including water droplets' falling in stagnant air and silicon oil droplets' rising in stagnant water.Droplets' motion was recorded by the high speed camera.Image dealing code was developed to deal with the vast photos.And water droplets' and silicon oil droplets' aspect ratio,surface oscillation period and drag coefficient were computed.Sufficient validation data were achieved.Then the D and PD method were validated entirelybyperforming lots of computation cases.Using the above numerical methods,the droplet's drag forces with different Rep?We were investigated under the thermal state of the steam drier inside the steam generator.And the drag model for the thermal state was built.To validate this drag model,the simulation code for the disperse phase was written to calculate the droplets' trajectoriesand the steam drier's separation efficiency.And the drag model for the thermal state was embedded in the simulation code.By writing CUDA C code,GPU parallel computation was employed to speed up the simulation of large amounts of dropletssignificantly.The separation efficiency of one wave-type vane drier with single hook was calculated and compared,which matched the experimental data.As a conclusion,the drag model for the thermal was accurate.Innovations of this work are: Accurate and generic numerical methods were built to calculate the droplet's drag force,which are more stable and efficient than previous methods and can be used to research phenomena on droplets' drag force,such as deformation,internal circulation,surface oscillation and so on.Using the above numerical methods,the drag model for the thermal state was built,which lays the foundation for the analysisof the steam drier' performance as a fundamental force model.Base on GPU parallel acceleration,efficient simulation code for the disperse phase was developed to calcaulate the steam drier's separation efficiency.