Unequal Head Hydraulic Design Theory Research For Impeller Of Centrifugal Pump

Centrifugal pumps are widely used in agricultural irrigation, municipal works, light industry, chemical industry, construction, mining, metallurgy and other departments. With the development of society and technology, people bring forward higher requirements on the pump's high efficiency, stability and low noise, and other aspects of the more stringent requirements. The hydraulic design methods widely used in centrifugal pump, is mainly based on the experience of Stepanoff similarity coefficient method based design. This method is characterized by a summary of the previous design and manufacturing experience, particularly the application of computer used in building a hydraulic model of the database, then, according to the required flow, head, choose a suitable specific speed hydraulic model from the database to design a similar pump to meet production needs. However, nowadays centrifugal pump operating point parameters (such as flow, head, etc.) increasingly requires high precision, the traditional unitary theory increasingly shows the deficiency of the design.Through the design research programs of three centrifugal pump with the same head, it's found that the blade outlet flow of centrifugal pump is not ideal; using differ head design method, respectively, in three centrifugal pumps hydraulic design, Good blade export total pressure program were obtained good blade export total pressure, static pressure, static pressure and velocity distribution are obtained. CFD and numerical simulation technology is used in the two design methods for steady and unsteady numerical simulations, confirming the superiority of the design method for centrifugal pump blades. Finally Experimental studies and comparative analysis in the design of centrifugal pumps using differ head design method and equal head method is done, which further confirmed the correctness of the design theory of centrifugal pump impeller. In the paper, the research work and innovations are:1. Comprehensive and systematic analysis of the hydraulic design of centrifugal pumps Research and Development of methods at home and abroad, the traditional centrifugal pump for the hydraulic design of similar algorithms, the speed coefficient, area ratio principle, optimal design method, ternary theories were introduced describing a wide range of application progress of numerical simulation in the hydraulic design of centrifugal pumps, pointing out the current method of hydraulic design deficiencies, and presenting differ chordwis circulation design method in circulation areas such as fans and axial flow Research and Application.2. Differ head design method is introduced in centrifugal pump impeller hydraulic design for the first time. Through the study of traditional method of centrifugal pump hydraulic design,it has been found that the traditional method of hydraulic design of centrifugal impeller will lead to unsatisfactory flow in the blade outlet, while using differ head method in the design of centrifugal pump, can get a good blade outlet total pressure, static pressure and velocity distribution.3. CFD technology is used in the design of the centrifugal pump to analyze the steady and unsteady flow in the centrifugal pump designed by differ head method. In the steady calculation,static pressure of each model, absolute speed, relative speed, scroll speed and impeller outlet section of the pressure distribution before and after the cover were obtained, revealing the flow pattern inside the pump mode. Through analysis and comparison of differ design and equal head design of hydraulic performance, the advantages obtained by differ head method is obvious and according to the flow rate statistics in different models, forecast performance curve has been drawn, summarized the design of programs using differ head method was the best design model.The combination of unsteady numerical simulation verifies that impeller and volute due to the interaction between the flow in centrifugal pump shows a strong unsteady state, not onlye the flow of the impeller respectively passageway structure at the same time is differential, but also flow structure in the rotation process at the same passageway is also changing, and it shows a cyclical fluctuations, which causes that various locations along the circumferential volute exists in the periodic pressure fluctuation,pressure pulse amplitude and frequency the maximum amplitude of the P values corresponding to the main frequency the product of frequency and number of leaves and produce pressure fluctuation is the main factors resulting in pressure fluctuation.4. According to previous simulation results, the pump performance can be predicted, however, compared with the performance curve obtained through the outside performance test, we can also assess the accuracy of numerical simulation certainly to verify the reliability of numerical prediction. The main reason:It only contains the hydraulic efficiency rather than mechanical efficiency and volume efficiency of Predictive value, and the numerical simulation idealized the flow of centrifugal pump,but the actual operation can not be less than ideal and the actual operation may produce bubbles, Therefore, it generally higher than the predicted experimental head. The size of the error number is related with the number of leaf: The more of the leaves, the bigger of the error.5. Differ head hydraulic design method is applied to double- blades sewage pump,water plant and nuclear power plants cooling water circulation pumps for the first time, and the results show that:(1) design of double-blades hydraulic sewage pump has a good hydraulic properties, head curve linear decline, no hump, and efficient district wide. (2) water plant pumps, efficiency in the design of the highest operating point value, the maximum efficiencyη=85%, similar products with the efficiency of the company KSBη=82% compared to 3 percent increase, efficiency indicators reaches international advanced level. (3) nuclear power plant cooling water circulation pump hydraulic model has high efficiency. High pump conversion efficiency to the real pump is 92.3%, efficiency rating points is 92%, effective district is wide.And efficiency indicators have reached international advanced level of similar pumps.