The influence of inducer rotation speed on the propagation characteristics of rotating cavitation and on the unsteady characteristics of cavitation in rotating cavitation and cavitation surge were examined using a three-blade inducer, which is named THK inducer, to develop the rocket engine turbopump that can operate stably over a wide operating range. The novel point of the paper is focusing on the cavitation itself, which is the cause of cavitation instabilities. The paper conducted two types of experiments using an inducer and single hydrofoils, and the dimensional and non-dimensional unsteady characteristic, which is the frequency of unsteady cavitation and the Strouhal number, were evaluated. Three types of rotating cavitation and cavitation surge were observed in the inducer. For a given cavitation number, the Strouhal number of rotating cavitation and the frequency of unsteady cavitation in cavitation surge are independent of the inducer rotation speed, respectively. The characteristic of rotating cavitation corresponds to that of cavitations arising in hydrofoils, but its characteristic of cavitation surge does not correspond. The dynamic characteristic of cavitation compliance in cavitation surge is similar to that of several rocket engine turbopumps. Therefore, it was proved that rotating cavitation is a cavity oscillation and cavitation surge is a system oscillation. Additionally, in a flow field with the same flow coefficient and different impeller rotation speed, the unsteady characteristics of cavitation instabilities are equal if the cavitation number is equal, which is named the “similarity law of cavitation number on cavitation instability”.
It is known that particle size obtained from Brownian motion of a particle is called the diffusion coefficient equivalent size (DCES) and is close to the geometric size independent of the physical properties of a particle. In this paper, it is described that real time measurement of the particle size and particle number concentration by observing the Brownian motion of the particles from which the influence of the flow field has been eliminated by the instrument combining the flow particle tracking (FPT) method and the L-shaped flow cell. Furthermore, we realized in evaluating the refractive index, which is the physical property information of the particles, from the DCES, the Rayleigh scattering equation and the light scattering intensity of particle that physical properties are known. In this paper, we also discuss that improvement of particle size accuracy and refractive index accuracy in the measurement of DCES. Index Terms-Brownian motion, diffusion coefficient equivalent size (DCES), flow particle tracking (FPT) method, physical properties of a particle, refractive index.
The phenomenon that a cavity rotates faster than the rotational speed of the pump in the direction of rotation is called super-synchronous rotating cavitation (super-S RC). It is known that super-S RC is often observed in rocket turbopumps, but that it is rare to be observed in industrial pumps. Therefore, we form a hypothesis that its occurrence is related to the rotational speed of pumps. In this study, experiments of an inducer were conducted at four rotational speed at Kakuda Space Center in the Japan Aerospace Exploration Agency. The pressure fluctuation and the rotor vibration were measured, and the propagation velocity ratio of super-S RC and the frequency of unsteady cavitation in the super–S RC were determined at each rotational speed. As a result, when the cavitation number is the same, the propagation velocity ratio is almost the same regardless of the rotational speed of the inducer. It means that the faster the rotational speed, the faster the unsteady cavitation oscillates in the inducer despite the condition of the same cavitation number. It indicates that rotating cavitation does not occur under a certain rotational speed because of the limitation of the frequency of unsteady cavitation, which is known in hydrofoil.
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