Research On The Hydraulic Characteristics And Sediment Particle Movement Distribution Of Bidirectional Twin Screw Pump By CFD

In ship transportation and urban drainage,two-way drainage function is needed in marine propeller,bidirectional injection/drainage depth control pump,cabin balance system,bilge pump,urban sewage discharge and other occasions,the traditional vane pump and volume pump can not meet their functional requirements,so it is necessary to develop bi-directional pumps for this special application.Two-way axial flow pump and mixed flow pump have the characteristics of low head and easy cavitation,which can not meet the design requirements of high head two-way drainage.Two-way twin-screw pump belongs to rotary volume pump,it has the characteristics of large flow,low noise,small vibration and smooth liquid delivery,it can realize the two-way drainage function of the screw pump by reversing the motor,and the difference between positive and negative performance is small,it is also suitable for applications with trace impurities,large flow and high discharge pressure.In this paper,CFD numerical simulation method is used to study the flow characteristics and hydraulic performance of the two-way twin-screw pump in forward and reverse operation,the flow law of the two-way twin-screw pump in forward and reverse operation and the movement and distribution law of sediment particles in the two-way twin-screw pump are revealed.(1)Using software SCORG and Pumplinx,the residual curves of standard k_? model and RNG k_? model are compared when choosing turbulence model.Finally,the standard k_?turbulence model is selected for simulation calculation.According to the grid independence,the total number of meshes is determined to be 1.87 million.(2)Parameter design of bidirectional twin screw pump.The design parameters of the two-way twin-screw pump are as follows:the size of the pump group is less than 1400 mm× 720 mm × 1950 mm,the design speed is 1600 rpm,the profile is composed of internal and external cycloids,the number of main and follower screw heads are all three-head spirals,and the screw lead is 300 mm.The theoretical flow rate of the developed two-way twin-screw pump meets the design requirements.(3)Flow characteristics of two-way twin-screw pump in forward and reverse operation.When the pump runs in both directions,the pressure value of the screw rotor increases step by step along the direction of medium flow,and the surface pressure of the screw rotor increases with the increase of head or speed.When the pump is running forward,the low pressure is at the end of the screw inlet and the high pressure is at the end of the screw outlet,the lower the speed,the larger the whirlpool area at the corner of the pump inlet,and the flow line is at the rest of the position is smooth.When the pump is running backward,the screw outlet end is low pressure and the inlet end is high pressure,compared with the forward operation,the number of low pressure chambers increases and the number of high pressure chambers decreases,there is a small area of reflux zone at the connection between the screw outlet and the screw rotor,the streamline in the other places is not abnormal.(4)Hydraulic performance of bidirectional twin screw pump under different operating condition.Under the same speed condition,the flow rate decreases with the increase of head and the power increases with the increase of head.Under the same head condition,the flow,head and efficiency of the pump in forward and reverse operation increase with the increase of speed.Under the same speed and head condition,the flow,power and efficiency of reverse operation are less than that of forward operation.(5)Effect of clearance of two-way twin screw pump on hydraulic performance.The results show that when the clearance between rotor and stator is 0.02mm,the power of the rotor is larger,the flow rate is smaller,and there i5 a large leakage zone in the clearance.When the clearance is greater than 0.05mm,the flow rate of the forward and reverse operation of the screw pump decreases gradually with the increase of the clearance,and the power of the rotor decreases first and then tends to be stable.The axial clearance and the clearance between the top circle and the root circle have little influence on the forward and backward flow rate of the screw pump,but have great influence on the rotor power.(6)Motion and distribution of sediment particles in two-way twin-screw pump operating forward and backward.The total amount of sediment particles increases obviously with the passage of time and tends to be stable after two rotating cycles when the screw pump operates in both positive and negative directions.The total amount of sediment particles in the pump increases first and then decreases with the increase of rotational speed.The total amount of sediment particles decreases with the increase of sediment particle size.During the five operation cycles of the pump,the sediment particles at the screw rotor diffuse from the rotor inlet to the outlet,and the sediment particles at the rotor outlet diffuse to the outlet.When the pump runs in reverse direction,the sediment particles at the screw rotor diffuse from the inlet end of the rotor to the outlet end,and the sediment particles at the outlet end of the rotor diffuse.