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大型抽沙泵揚程怎么計算

1. 計算域部分

理論上,離心泵從進口到出口的流動區域為模型計算域，可分為葉輪進口段、葉輪、泵體前腔、泵體后腔、泵體(蝸殼)及出口段。通常的計算中常常忽略葉輪與蝸殼間軸向間隙，只取進口段、葉輪、蝸殼及出口段作為計算域。計算域的空間離散也即計算網格劃分過程，可采用非結構化四面體或結構化六面體網格借助商業軟件Gambit、ICEM、Pointwise或Turbogrid等進行。
2.動靜區域耦合計算方法
    由于計算區域中存在動靜區域耦合問題(靜止的進口區與旋轉的葉輪區，旋轉的葉輪區與靜止的蝸殼區域),通常對于定常情況下的計算采用多重參考系(Multiple Reference Frame)方法，假定葉輪不轉，僅在葉輪區域內動量方程計算中考慮因旋轉而額外產生的項，動靜區域間設置交界面以傳遞動量;對于非定常情況下的計算一般采用滑移網格技術(MovingMesh)來考慮動靜區域的耦合問題。
3.湍流計算模型
    湍流的數值模擬方法總體上可分為直接數值模擬和非直接數值模擬兩大類。直接數值模擬通過直接求解瞬時湍流控制方程來求解流場；而非直接數值模擬則需要將湍流做某種程度的近似和簡化處理后，通過求解簡化后的控制方程來求解流場。根據湍流瞬時控制方程的近似和簡化方法不同，非直接數值模擬又分為大渦模擬與雷諾平均數值模擬。對于離心泵而言,其湍流模型的選取還需要考慮高速旋轉、流道間存在的較大逆壓梯度及葉片面與流道曲率的影響。
4.邊界條件設置
    (1)對于泵的進口:一般來說給定流量來計算揚程，通常設置為速度進口或質量流量進口:若需要根據揚程來計算流量，則要給定進口壓力(相應出口給定壓力出口條件)，即進口壓力條件。
    (2)泵的出口:通常給定自由出流或壓力出口條件(計算中出口回流量較大時，選用壓力出口較為適宜)。
    (3)固壁表面:無滑移壁面條件(旋轉葉片區內壁面設置相對速度為零，蝸殼壁面設置絕對速度為零)。
    選取某一單級單吸離心泵為例進行CFD模擬,計算中選取進口段、葉輪、蝸殼及出口段作為計算域，如圖1- 107所示，其空間離散后隔舌處局部網格如圖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.