Study on hydraulic design of centrifugal pump

1. Development of domestic hydraulic model

The hydraulic model design method of centrifugal chemical pump basically refers to ordinary centrifugal pump, so the relevant technical progress is basically consistent with ordinary centrifugal pump. Before the internal flow state of centrifugal pump has not been fully understood and mastered by people, a complete and accurate design theory has not been formed. For a long time, centrifugal pump technology has been a semi theoretical and semi empirical technology. A successful hydraulic model design often needs repeated modification and test. When designing new products, most technicians can only find hydraulic models with equal or similar specific speed for similar conversion. Therefore, hydraulic models are very important in new product design.

In the 1970s and 1980s, Shenyang Water Pump Research Institute, China Agricultural Machinery Research Institute, Boshan water pump factory, China Agricultural University and other units carried out a lot of work in the development of centrifugal pump hydraulic model and accumulated many excellent hydraulic models. Shenyang Pump Research Institute is responsible for organizing and successively publishing two issues of "centrifugal pump hydraulic model compilation", which provides a rich model base for centrifugal pump hydraulic model design of domestic enterprises.

2. Traditional hydraulic design method

2.1 similarity transformation algorithm

Similarity conversion method is a method based on similarity theory. The pump size to be designed is obtained by enlarging or reducing the size of similar model pump on the basis of a model pump. For completely similar pumps, the specific speed is equal. Under similar working conditions, assuming that the efficiency of the real pump and the model pump is equal, the geometry and performance parameters of one pump are known, and the similarity law is used to enlarge or reduce it to another pump with similar geometry in proportion, and the corresponding performance curve is converted. This design method requires a hydraulic model library.

2.2 velocity coefficient method

The velocity coefficient method is designed based on the velocity coefficient diagram. In essence, it is still a similarity transformation algorithm based on the similarity theory. It also requires a good pump model, and the speed coefficient is selected according to N in the design as the basis of hydraulic size. Their coefficients are obtained when the specific speed is greater than or equal to 30R / min, which limits their use in the design of low specific speed and ultra-low specific speed centrifugal pumps. At present, many people have improved this diagram and used this method to design and optimize the pump.

2.3 area ratio principle design method

The area ratio design method is designed according to Anderson's area ratio principle, that is, it uses the area ratio to draw the form of head coefficient and flow coefficient to correct the standardized design data. The purpose is to find the best matching between impeller and pump body according to different design requirements; The basis is that different impeller and pump body matching will produce different pump performance; Its essence is to consider the impeller and pump body as a whole; The method is the optimal design considering the design parameters, economy, manufacturability and reliability.

2.4 increased flow design method

The increased flow design method is based on the fact that when the low specific speed pump operates in a small flow range, the efficiency increases rapidly with the increase of flow, and takes the amplification of given flow and specific speed as design parameters to design a larger pump to be used as a small pump at a small flow. Such a pump not only greatly improves the efficiency at the design point, but also improves the average efficiency in the whole service range to a certain extent.

2.5 short blade offset method

The purpose of short blade offset design is to improve the speed and pressure distribution of centrifugal pump impeller and pump body, so as to improve the performance of the pump. The basis is that the velocity and pressure distribution in the impeller change with the shape of impeller channel and blade; The method is to optimize the design considering the design conditions, channel geometry and manufacturability; The main measure is to set an ultra short blade in the middle of the two adjacent long blades and offset to the back of the long blade; The bad consequence is that it may bring difficulties to the casting process.

3. Progress in hydraulic design

At present, the unitary design theory based on empirical data and design theory has been quite mature. The unitary design theory is also a widely used design theory, and people have accumulated many excellent hydraulic models in the design process. Therefore, for ordinary chemical pump products, designers have been able to design some models with excellent hydraulic performance, and can better meet the use requirements of users.

The internal flow of centrifugal pump is a full three-dimensional complex flow. Ordinary designers have limited understanding of the internal flow characteristics. For some special-purpose centrifugal pumps, the hydraulic model designed by using the one-dimensional design theory can not fully meet the requirements. Therefore, optimization design also appears. In the initial stage, based on the experience-based unitary design, it adopts the optimization design theory and optimizes the hydraulic model and structural parameters with some parameters as the objectives to obtain better hydraulic performance. In the process of optimization design, there are problems of performance prediction and flow analysis. For the flow analysis and performance prediction of hydraulic rotating machinery, computational fluid dynamics (CFD) technology has been widely used for three-dimensional numerical simulation of the whole flow field. Based on the flow field simulation to predict the performance, improve the flow structure that is not conducive to the improvement of performance, improve the blade load and improve the efficiency. Through years of development, this kind of method can be better used in the engineering design and optimization of centrifugal pump.

The optimization design of centrifugal pump based on three-dimensional flow simulation of internal flow field will be an important means and is becoming a key step in the design process of centrifugal pump. Combined with inverse problem design technology, CAD technology, CAM technology and artificial intelligence technology, it can realize the rapid and intelligent design and manufacturing of efficient hydraulic model.

Based on the application requirements and the needs of developing centrifugal pump technology, and relying on the technical development in the fields of computer, computational fluid dynamics and computer-aided design, people have carried out a lot of work in the improvement of unitary design method, optimization design and internal flow numerical simulation, including the more advanced CAD / caf interactive design technology abroad, The design of centrifugal pump gradually develops from one-dimensional flow design to three-dimensional flow design. These works have promoted the development of centrifugal pump design theory and significantly improved the hydraulic performance of many centrifugal pumps, including centrifugal chemical pumps.