Calculation and Improvement of Internal Flow Field of Large Diameter Butterfly Valve

   1 calculation model

1.1 Geometric Modeling

     The three-dimensional modeling of the disc was first carried out using Solidworks software (see Figure 1). The diameter of the bottom of the disc is 3.4 m. The upper part of the butterfly is designed as an arched structure, and the inside of the arch is designed with a plurality of gratings to increase the water flow area. There is a boss on each side of the arch for mounting the shaft of the disc.

Figure 1 3D modeling of the prototype butterfly

     According to the preliminary analysis, the bosses on both sides of the arch may cause the flow disorder, so it is transformed into a streamlined shape, and its three-dimensional shape is shown in Fig. 2.

Figure 2 3D modeling of the improved disc

    1.2 Calculation modeling

     The calculation model uses a three-dimensional NS equation and a standard k-ε turbulence model. Its main governing equation is:

     In equation (1), Q is a conservation variable vector; f, g, and h are fluxes in three coordinate directions, respectively, expressed as equations (2) to (5):

    

     The stress term is the second page (6).

     Solve using the standard k-ε model. For the specific equations, see Equations (7) and (8) on page 2. In equations (7) and (8), G _k is the turbulent flow energy, ε is the turbulent flow energy dissipation rate, and σ _k and σ _ε are the Prandtl numbers of k and ε, respectively.

        (6)

        (7)

        (8)

        (9)

     Where S is the modulus of the average strain rate tensor and μ _t is the turbulent viscosity,

        (10)

     The values ​​of the constants in the model are as follows:

C _{1 ε} =1.44 , C _{2 ε} = 1.92 , C _μ =0.09 , σ _k =1.0 , σ _ε =1.3 . (11)

     Calculation conditions: flow inlet speed 5 m/s, inlet pressure 100 kPa.

    2 calculation results and analysis

     According to the inlet flow rate of the valve before the inlet is 5m/s and the inlet pressure is 100kPa, the dynamic mesh technology is used to obtain the flow field change during the dynamic process of the butterfly plate (see Figure 3).

Figure 3 Flow change during valve opening process

     The calculation also shows the flow diagram and pressure cloud diagram of the two discs in the horizontal (ie full-open) state before and after the improvement (see Figure 4, Figure 5, Figure 6, Figure 7 on page 3). As can be seen from the streamline diagram, the flow near the prototype valve disc is more turbulent, and the improved flow is smoother. Reflected in the pressure, it can be seen from the pressure cloud diagram that the pressure gradient before and after the improvement is significantly different. The prototype butterfly plate has obvious pressure concentration on the bosses on the both sides and the outer ribs, which is easy to cause structural damage, and the pressure distribution of the improved butterfly plate is relatively uniform.

Figure 4 prototype butterfly streamline (speed)

Figure 5 Improved butterfly streamline (speed)

Figure 6 Prototype butterfly pressure cloud (gauge pressure)

Figure 7 Improved disc pressure cloud (gauge pressure)

     From the calculation results, the improved disc has the obvious advantage of "large flow coefficient, small pressure loss".

     The more practical data is the flow coefficient and the pressure loss coefficient. The calculations in this paper also give the relevant results before and after the improvement (see Table 1).

Table 1 Pressure coefficient and flow coefficient before and after the improvement of the disc

     It can be seen from the calculation results in Table 1 that the resistance of the improved butterfly plate is reduced by about 30%, the pressure difference is reduced by 9%, the pressure loss coefficient is reduced by about 9%, and the flow coefficient is increased by 5%.

  3 economic analysis

     The butterfly valve plate is formed by a casting process. After the improvement, the material cost increased by about 5%, the processing technology did not change much, and the total manufacturing cost increased slightly. However, the improved valve has a streamlined convex table on both sides, and the stress concentration of the joint portion is greatly improved, and the damage is less likely to occur under large load conditions, so that the valve failure rate is significantly reduced, and the service life is significantly prolonged; Moreover, the energy loss during the water delivery process is reduced, and the work efficiency is improved. In comparison, the increase in manufacturing costs is completely negligible.