Front Impeller Research Articles

Smart Control of Axial Flow Pump Performance by Means of Counter-Rotation

Turbo pumps have weak points, such as the pumping operation becoming unstable in the rising portion of the head characteristics and/or the cavitation occurring under the intolerably low suction head. These points have been individually overcome in general, since such phenomena originate in essentially different causes. To overcome the above weak points simultaneously, however, we propose a unique pumping system with counter-rotating mechanism and discuss its advantages. This system consists of two-stage impellers and a unique motor with double rotors. The front and rear impellers are driven respectively by the inner and outer rotors of the motor, keeping the relative rotational speed constant and counter-balancing the rotational torque. Such driving conditions not only improve smartly the unstable performance at low discharge but also suppress smartly cavitation at high discharge, under the optimum cooperation with the impeller works and the rotor outputs. The model test proved that there is no rising portion of the head characteristics and that the front impeller speed is gradually decreased with increase of the discharge as if taking the place of the inducer.

Smart Control of Axial Flow Pump Performances by Means of Counter-Rotating Type. 1st Report. Counter-Rotating Type and Performances.

This paper proposes a unique counter-rotating type of the pumping system which is composed of the two-stage impellers and the peculiar motor with the double rotors, and discusses remarkable advantages of the system. The front and the rear impellers are driven by the inner and the outer rotors, respectively, keeping the relative-rotational speed constant and keeping the counter-rotational torques same. Such operating conditions make not only the unstable performance in the low discharge but also the cavitation in the high discharge suppress smartly, in the optimum cooperation with the impellers and the rotors. The model test proved that there is not the rising portion of the head characteristics and the front impeller speed decreases with increase of the discharge as if the impeller takes the place of the inducer.

Aerodynamically Induced Radial Forces in a Centrifugal Gas Compressor: Part 2—Computational Investigation

Radial loads and direction of a centrifugal gas compressor containing a high specific speed mixed flow impeller and a single tongue volute were determined both experimentally and computationally at both design and off-design conditions. The experimental methodology was developed in conjunction with a traditional ASME PTC-10 closed-loop test to determine radial load and direction. The experimental study is detailed in Part 1 of this paper (Moore and Flathers, 1998). The computational method employs a commercially available, fully three-dimensional viscous code to analyze the impeller and the volute interaction. An uncoupled scheme was initially used where the impeller and volute were analyzed as separate models using a common vaneless diffuser geometry. The two calculations were then repeated until the boundary conditions at a chosen location in the common vaneless diffuser were nearly the same. Subsequently, a coupled scheme was used where the entire stage geometry was analyzed in one calculation, thus eliminating the need for manual iteration of the two independent calculations. In addition to radial load and direction information, this computational procedure also provided aerodynamic stage performance. The effect of impeller front face and rear face cavities was also quantified. The paper will discuss computational procedures, including grid generation and boundary conditions, as well as comparisons of the various computational schemes to experiment. The results of this study will show the limitations and benefits of Computational Fluid Dynamics (CFD) for determination of radial load, direction, and aerodynamic stage performance.

An Experimental Investigation of Stator Induced Unsteadiness on Centrifugal Impeller Outflow

Detailed flow measurements were taken in a centrifugal turbomachine model to investigate the aerodynamic influence of the vaned diffuser on the impeller flow. The model consists of an unshrouded centrifugal impeller with backswept blades and a rotatable vaned diffuser, which enables a continuous variation of the vaned diffuser location with respect to the measuring points. Phase-locked ensemble-averaged velocity components have been measured with hot-wire probes at the impeller outlet for 30 different relative positions of the probe with respect to the diffuser vanes. The data also include the distribution of the ensemble-averaged static pressure at the impeller front end, taken by means of miniature fast response pressure transducers flush-mounted at the impeller stationary casing. By circumferentially averaging the results obtained for the different circumferential probe locations, the periodically perturbed impeller flow has been split into a relative steady flow and a stator-generated unsteadiness. The results for the different probe positions have also been correlated in time to obtain instantaneous flow field images in the relative frame, which provide information on the various aspects of the diffuser vane upstream influence on the relative flow leaving the impeller.

ＬＥ‐７液酸ターボポンプの軸推力釣合わせ

A self-balancing type axial-thrust balancing system referred to as “balance piston” was applied to the LE-7 LOX turbopump, the discharge pressure of which exceeds 30MPa. A research model turbopump showed that pressure distribution in the balancing chamber deviated greatly from the predicted distribution and that the axial clearance of the balancing-chamber inlet orifice became too small to maintain safety. Consequently, we attempted to determine the cause of these phenomena and to find methods of ensuring sufficient axial clearance of the inlet orifice. Two methods were attempted. In the first method, balancing holes directly connecting the balancing chamber and the main impeller inlet were made. In the second method, grooves were made on the casing wall facing the main impeller front shroud.