sampling points are located near the throttling section.

cted as required,

px     is the positions of the   pressure

The locations of all 7 points are shown in Fig.3 too.

The FLUENT software is used to solve the gove- rning equations for the water phase. As the height    of

measuring point in the passage. The CFD simulation boundary conditions for this case are as follows: the water temperature is 15oC, the inlet velocity is 9.5 m/s,

the inlet static pressure is 355.6 kPa and the outlet sta- tic pressure is 118.1 kPa. The Reynolds number is 1.315×105 correspondingly at the inlet section. The results indicate that the difference is very small. For

3.2 The pressure and the velocity in the passage

Figure 5 shows the pressure contours and the velocity vectors of the prototype channel in the follo- wing  case:  the  inlet  velocity  is  6.33  m/s (Reynolds

example, the maximum difference is at point 6, which is  about  4.5%.  Therefore,  the  2-D  CFD simulation

number

1.6 kPa.

Re = 1.051105   )   and   outlet   pressure   is

approach  is valid  to investigate the characteristics  of

the pressure and the velocity in the labyrinth passage.

3. Numerical results of prototype passage

The numerical results of the contours in Fig.5(a) show that the pressure in the “series passage” is dro- pped from 400 kPa  to  165  kPa,  the  difference  is 335 kPa. While the pressure difference in the “parallel passage” is only about 163.4 kPa. That is, the former contributes  about  83.8%  of  the  total  pressure drop.

3.1 The boundary conditions

The pressure loss coefficient

= 16.72 .

The geometrical structure of the prototype   pass-

age is shown in Fig.2. The boundary conditions for different cases are listed in Table 2.

Table 2 The boundary conditions for 3 cases

Case Re Inlet

velocity/ Outlet

pressure/ Water

temperature/

ms−1 kPa oC

1 1.051×105 6.33 1.6 15

2 8.304×104 5.00 102 15

3 5.531×104 3.33 243 15

Fig.5 Flow characteristics of labyrinth passage for Case 1

The velocity vector depicted in Fig.5(b) indicates six large vortex areas in the passage where the right angle turns are distributed along the flow direction. It is also shown that from the first vortex to the fifth in the “series passage”, the area of the vortex section is increased gradually, but every vortex density eddy still maintains at a reasonable level without dramatic cha- nges. Judged from the density variations of the stream lines, they vary also gently. It denotes that the pressu- re drops evenly too, thus the energy losses are kept within a certain range through each corner.

Fig.6 Flow characteristics of labyrinth passage for Case 2