Effects of inducer tip clearance on the performance and flow characteristics of a pump in a turbopump

Abstract

A turbopump is used to pressurize propellants to gain high thrust in a projectile and consists of two pumps and a turbine. The pumps usually employ an inducer upstream to prevent performance deterioration by lowering net positive suction head required of the main impeller. However, several types of cavitation and instabilities take place in the flow field. Therefore, numerous experiments and CFD analysis for turbopumps have been conducted. Especially, there were some previous studies on inducer tip clearance, but they were limited to inducer regions due to the complexity of simulating the entire pump. In this study, the flow through an oxidizer pump in a turbopump was numerically investigated with four different sizes of inducer tip clearances. ANSYS CFX 13.0 with Rayleigh–Plesset equation was used to test flows in both non-cavitating and cavitating conditions. In the non-cavitating condition, the pump with the largest inducer tip clearance showed the worst head rise, efficiency and huge size of backflow arose near inducer casing. Also, the vortex was generated between the inducer blades in the case of large inducer tip clearance due to weak tip leakage flow. In the cavitating condition, the inducer with large tip clearance was found to be vulnerable to low suction pressure and floating cavity was observed between the inducer blades. However, the heads of the pumps with different inducer tip clearances were broken down at similar cavitation numbers due to the blade cavitation near the impeller throat. In addition, the transferred cavity from the inducer region also induced head breakdown of the pump.

Numerical simulation of the performance of a centrifugal pump with a semi-open impeller under normal and cavitating conditions

“…11 and 12. Here, Ψ value increased with the decrease of tip clearance thickness and was maximized at the case with the minimum tip clearance, due to the minimization of leakage flow passage along with the tip losses and vortex recirculation similarly to [64,[75][76][77]. Similar behavior follows the efficiency of the pump due to the increase of the tip clearance losses.…”

Numerical analysis for the effect of tip clearance in a low specific speed mixed-flow pump

“…Also, the hydraulic loss can be made by the disturbance of the tip leakage flow on the mainstream. 22,23 Therefore, the tip loss here represents the gross effect aroused from the tip leakage flow. Figures 13 and 14 show the velocity vector and the pressure distribution near the pressure surface, respectively.…”

Improvement of cavitation erosion characteristics of the centrifugal inducer stage with the inducer bush

“…The results of long experience in designing of inducers installed in the first centrifugal inducer stages of industrial pumps, which can be used to assess the modern achievements in this field, are presented in [5]. The study [6] analyzes the effect of the clearance between the inlet casing and the inducer, and also states that cavitation erosion most often occurs in the peripheral areas of the inducer. Hence, the emphasis should be on this area of the centrifugal inducer stage which in the classic design (Fig.…”