The numerical simulation based on CFD of hydraulic turbine pump

As the functions of hydraulic turbine pump including self-adjusting and compensation with each other, it is far-reaching to analyze its internal flow by the numerical simulation based on CFD, mainly including the pressure field and the velocity field in hydraulic turbine and pump.The three-dimensional models of hydraulic turbine pump are made by Pro/Engineer software;the internal flow fields in hydraulic turbine and pump are simulated numerically by CFX ANSYS software. According to the results of the numerical simulation in design condition, the pressure field and the velocity field in hydraulic turbine and pump are analyzed respectively .The findings show that the static pressure decreases systematically and the pressure gradient is obvious in flow area of hydraulic turbine; the static pressure increases gradually in pump. The flow trace is regular in suction chamber and flume without spiral trace. However, there are irregular traces in the turbine runner channels which contrary to that in flow area of impeller. Most of traces in the flow area of draft tube are spiral.


Introduction
Computational fluid dynamics (CFD), which is theoretical and practical, describes the numerical solution of the flow field quantitatively on the time and space by computer numerical calculations and a method of image displayed [1]. The relationship of performance parameters between pumps and PAT was predicted by theoretical analysis and the empirical formulas based on the experimental data [2]. However, turbine Pump has some advantages ， such as low cost and the ability of simulating complicated or desirable fluid motion. As the functions of hydraulic turbine pump including selfadjusting and compensation with each other , it is far-reaching to analyze its internal flow.

Mesh generation of fluid region
The number of grid of hydraulic turbine is 1158877 and pump is 1458943. The grids are presented in figure4 to figure5 [4].

Turbulence Model
At present , the standard k-ε model is the most basic one of the double equations model being the most widely used the eddy viscosity model. The equations [5] are as follows :

The simulation and analysis of internal flow field in pump and hydraulic turbine
The inner flow field in pump and hydraulic turbine are simulated by ANSYS CFX ,and then the velocity profile and pressure profile are analyzed to get some conclusions through the pictures from the simulation.

The analysis of pressure profile in hydraulic turbine
The pressure value compared to 101325 Pa is a relative value in this model [6].

Figure 6.
Static pressure distribution diagram of hydraulic turbine From Figure6 ,the static pressure is lower and lower as the order of intake pipe , turbine flume ,impeller and draft tube. The dividing line is obvious among the different pressure fluid ,and the static pressure value is rather low in the draft tube.
The static pressure contours of the whole flow passage of hydraulic turbine are shown in Figure6. As can be seen from the picture, the static pressure of the water diversion chamber, the runner and the draft tube is decreasing in order .The indoor static pressure of the water diversion chamber begins to decrease from the IX section, which is decreasing as the diversion chamber flow section area reducing. Some regions appears high-pressure. The static pressure of the runner is decreasing from the inlet to the outlet and the pressure gradient is significant. The static pressure of draft tube is basically constant. The static pressure contours of the axial section of the whole passage of pump is shown in Figure7.As can be seen from the picture, the static pressure of the water inlet pipe, the water diversion ICPF2015 IOP Publishing IOP Conf. Series: Materials Science and Engineering 129 (2016) 012042 doi:10.1088/1757-899X/129/1/012042 3 chamber, the impeller, the water pressing chamber and the water outlet pipe is gradually decreasing in order. And the pressure gradient is significant. Figure 7.Static pressure contours of the whole passage of pump The static pressure contours of the whole passage of pump is shown in Figure7. As can be seen from the picture, the pressure of the suction chamber, the impeller, the pump chamber and the outlet pipe is gradually increasing .The the static pressure gradient of liquid impeller is significant, which is increasing gradually.
The indoor static pressure of the pumping chamber is decreasing from I section to XIV section. Some regions appeared high-pressure. The static pressure of impeller passage increased gradually from the inlet to the outlet direction, the adverse pressure gradient. And the pressure gradient is significant. The static pressure of outlet pipe is basically constant.

The analysis of velocity field of the internal flow region of the hydraulic turbine.
The velocity vector distribution of the whole flow passage of pump is shown in Figure8.The velocity vector distribution of the axial section of the whole flow passage is shown in Figure8. As can be seen from the picture, the velocity of the inlet pipe, the suction chamber, the impeller and the pumping chamber increase first ,then decrease. The liquid velocity value reached the maximum in the impeller. And it reached the minimum in the draft tube. The velocity field of inlet liquid in the tube is regular, which is spiral in the tail pipe and the outlet pipe. The velocity vector distribution of pump is shown in Figure11.As can be seen from the picture, the relative velocity of the suction chamber, the impeller, the volute and the outlet pipe increases first ,then decreases.
The liquid relative velocity value reached the maximum in the flow passage of the impeller. And it reached the minimum in the center of back cover plate. The velocity field in the suction chamber and the impeller is regular. And there is vortex of the velocity field in the volute. The velocity field in the outlet pipe is regular.

Conclusion
In the hydraulic turbine, the static pressure of the suction chamber, the impeller, the tail pipe is lower and lower, the pressure gradient is significant. In the pump, the pressure of the suction chamber, the impeller, the pumping chamber and the outlet pipe is gradually increasing .
The trace in the inlet pipe and the diversion chamber is regular, There is no spiral trace appearing. There is irregular trace appearing in the flow passage of the turbine impeller which contrary to in the follow passage of pump impeller. Most of trace in the tail pipe is spiral.