Pumps are machines in which liquid and machinery interact. The characteristic of the pump is an external expression of the movement of the liquid in the pump, and the movement of the liquid is determined by the geometry of the flow part. It can be seen that the analysis of the movement of the liquid in the pump determines the characteristics of the pump and designs its geometry. basis. The impeller is the core of the pump's work, and it is particularly important to analyze the movement of the liquid in the impeller.
The movement of the impeller itself is very simple, it just rotates with the shaft, but the liquid movement in the impeller is more complicated due to the action of the impeller blades, which is a compound movement. On the one hand, the liquid makes an impulsive motion as the impeller rotates, and on the other hand, the liquid continuously flows out from the rotating impeller, that is, it moves relative to the impeller. Observing the motion of the liquid in the impeller from the coordinates fixed on the land is the absolute motion, which is the combined motion of the implicated motion and the relative motion, that is, v = u + w.
In order to further analyze the motion of the liquid in the impeller, we adopt the method of integrating the whole into a partial, that is, layering the flow in the impeller. It is assumed that the liquids in each layer are not mixed with each other. When the number of layers is very large, a microelement flow layer is obtained.
This stream layer is consistent with the nature of the flow surface-the velocity at any point above it is tangent to it. Obviously, the inner rotating surfaces of the front and rear cover plates of the impeller are two boundary flow surfaces, and any number of similar flow surfaces (usually 1 to 3) can be divided in between.
In this way, studying the flow in the impeller is simplified to study the flow on several flow surfaces. The flow on several flow surfaces may not be exactly the same, but the research method is the same. Therefore, the flow of one flow surface is thoroughly studied, and the flow of other flow surfaces is similarly solved.
Figure (a) shows the flow surface of the rear cover. The line of intersection (blade section) of the blade and the flow surface is drawn on it. It can be said that this line of intersection is the flow line of the liquid relative movement in the impeller. Any number of such streamlines can be drawn between the leaves. Assuming that the blades are infinitely thin and infinitely thin, the shapes of these streamlines are exactly the same, so just study one streamline. The relative flow lines on several flow surfaces are regularly arranged, and the thickness is the surface of the blade in the impeller. In this way, the blade can be considered to be composed of several relative motion streamlines. Therefore, studying the flow in the impeller is simplified to studying the flow of the relative motion streamline. The streamlines of implicated motion, relative motion and absolute motion are shown in Figure (b).
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