大型抽沙泵扬程怎么计算

1. 计算域部分

理论上,离心泵从进口到出口的流动区域为模型计算域，可分为叶轮进口段、叶轮、泵体前腔、泵体后腔、泵体(蜗壳)及出口段。通常的计算中常常忽略叶轮与蜗壳间轴向间隙，只取进口段、叶轮、蜗壳及出口段作为计算域。计算域的空间离散也即计算网格划分过程，可采用非结构化四面体或结构化六面体网格借助商业软件Gambit、ICEM、Pointwise或Turbogrid等进行。
2.动静区域耦合计算方法
    由于计算区域中存在动静区域耦合问题(静止的进口区与旋转的叶轮区，旋转的叶轮区与静止的蜗壳区域),通常对于定常情况下的计算采用多重参考系(Multiple Reference Frame)方法，假定叶轮不转，仅在叶轮区域内动量方程计算中考虑因旋转而额外产生的项，动静区域间设置交界面以传递动量;对于非定常情况下的计算一般采用滑移网格技术(MovingMesh)来考虑动静区域的耦合问题。
3.湍流计算模型
    湍流的数值模拟方法总体上可分为直接数值模拟和非直接数值模拟两大类。直接数值模拟通过直接求解瞬时湍流控制方程来求解流场；而非直接数值模拟则需要将湍流做某种程度的近似和简化处理后，通过求解简化后的控制方程来求解流场。根据湍流瞬时控制方程的近似和简化方法不同，非直接数值模拟又分为大涡模拟与雷诺平均数值模拟。对于离心泵而言,其湍流模型的选取还需要考虑高速旋转、流道间存在的较大逆压梯度及叶片面与流道曲率的影响。
4.边界条件设置
    (1)对于泵的进口:一般来说给定流量来计算扬程，通常设置为速度进口或质量流量进口:若需要根据扬程来计算流量，则要给定进口压力(相应出口给定压力出口条件)，即进口压力条件。
    (2)泵的出口:通常给定自由出流或压力出口条件(计算中出口回流量较大时，选用压力出口较为适宜)。
    (3)固壁表面:无滑移壁面条件(旋转叶片区内壁面设置相对速度为零，蜗壳壁面设置绝对速度为零)。
    选取某一单级单吸离心泵为例进行CFD模拟,计算中选取进口段、叶轮、蜗壳及出口段作为计算域，如图1- 107所示，其空间离散后隔舌处局部网格如图1- 108所示。

How to calculate the lift of large sand pump

1. Computing domain

In theory, the flow region from the inlet to the outlet of centrifugal pump is the model calculation domain, which can be divided into impeller inlet section, impeller, pump body front cavity, pump body rear cavity, pump body (volute) and outlet section. The axial clearance between impeller and volute is often ignored in the calculation, and only the inlet section, impeller, volute and outlet section are taken as the calculation domain. Unstructured tetrahedral or structured hexahedral meshes can be used in the spatial discretization of computational domain, and commercial software gambit, ICEM, pointwise or turbogrid can be used.

2. Coupling calculation method of dynamic and static regions

Due to the coupling problem between the static and dynamic regions (the static inlet region and the rotating impeller region, the rotating impeller region and the stationary volute region), the coupling problem between the static and dynamic regions exists, Usually, the method of multiple reference frame is used to calculate the steady state. Assuming that the impeller does not rotate, only the additional terms due to rotation are considered in the momentum equation calculation in the impeller area, and the interface is set between the static and dynamic regions to transfer momentum; In the unsteady case, the moving mesh technique is generally used to consider the coupling problem of the static and dynamic regions.

3. Turbulence calculation model

The numerical simulation methods of turbulence can be divided into direct numerical simulation and indirect numerical simulation. The direct numerical simulation solves the flow field by solving the instantaneous turbulence control equation directly, while the indirect numerical simulation needs to solve the flow field by solving the simplified control equation after the turbulence is approximated and simplified to some extent. According to the different approximation and simplification methods of instantaneous governing equations, indirect numerical simulation can be divided into large eddy simulation and Reynolds average numerical simulation. For the centrifugal pump, the selection of turbulence model also needs to consider the influence of high-speed rotation, large adverse pressure gradient between the flow channels and the curvature of blade surface and channel.

4. Setting of boundary conditions

(1) For the pump inlet: Generally speaking, the head is calculated by the given flow rate, which is usually set as the speed inlet or mass flow inlet: if the flow rate needs to be calculated according to the head, the inlet pressure shall be given (the corresponding outlet pressure is given, and the outlet condition), that is, the inlet pressure condition.

(2) Pump outlet: usually given free flow or pressure outlet conditions (when the outlet return flow is large, the pressure outlet is more suitable).

(3) Fixed wall surface: no sliding wall condition (the relative velocity of the inner wall of the rotating blade area is zero, and the absolute velocity of the spiral case wall is zero).

A single-stage single suction centrifugal pump is selected as an example for CFD simulation. In the calculation, the inlet section, impeller, volute and outlet section are selected as the calculation domain, as shown in Fig. 1-107, and the local grid at the tongue after spatial discretization is shown in Fig. 1-108.