The Cavitation Performance Analysis And Assessment Of A Mixed Flow Pump Designed With Model Transformation Method

The nuclear main pump is the driving equipment in nuclear coolant cycling system, it’s also the unique revolving part in the nuclear island. And the nuclear main pump is required to operate under high temperature, high pressure and strong radiation surroundings in long term safely and reliably. Cavitation is a common reason of damage in hydraulic machinery, and it will cause noises, vibrations and decrease of hydraulic performance, sometimes even the damage of the blades, but all of these serious consequences must be avoided especially in nuclear main pump. In current conditions, the cost of experiments of nuclear main pump is very high, and numerical simulation is a more economical and fast means which simulates the flow field in nuclear main pump. In this paper, the flow field characters of blades of three different type pumps design by velocity coefficient method and model transformation method are simulated in the design flow rate conditions, and the cavitation characteristics are calculated and comparative analyzed.First of all, the research progress at home and abroad of nuclear main pump on both sides of design and cavitation performance are briefly introduced, and introduces the related parameters of cavitation and three cavitation model.Secondly, the cavitation flow around a two-dimensional airfoil is simulated with three cavitation models, and it is proved that the result of S-S model is in good agreements with experiment data. Then, the cavitation performance of a seven-blade-pump designed with model transformation method is analyzed under design flow rate and full flow rate. Under design flow rate, the blade’s NPSHr is50m, the head is135m, and cavitation won’t occur at the design pressure. While the NPSHr is204m, bubbles occur at the inlet of the blades. The cavitation process can be divided into three steps:no cavitation process, cavitation occurring process and growing partially process and seriously cavitation process. At the full flow rate, the cavitation performance curves are calculated within the limits of0.9-1.2times design flow rate. The results show that NPSHr significantly increases with flow rate, and the NPSHr are less than the pump required NPSII calculated by three methods. Because of the different of software, calculating field and calculating model, the efficiency is slightly different from Shen Fci’s result, but the result is still reasonable. The pump NPSH values at different flow rate calculated by three empirical formulas and the defined formula are greater than the simulated critical NPSH. Also, decreasing the blade inlet diameter can take both the cavitation performance and efficiency in count at the same time, the Blade inlet width has been appropriate.At last, the thermodynamie effects on cavitation flow in high temperature is discussed, ideas and methods are put forward to study the effects, the programming language of the source term and the coefficient of polynomial varying with temperature are given.