Study of the vortex chamber and its application for the development of novel measurement and control devices

Based on studies of the flow structure in a short cylindrical vortex chamber, the dependence of the flow rate coefficient on its geometric parameters is proposed. It is shown that the liquid flow form in the chamber’s axial vortex the pressure on which surface is corresponds to the pressure of the outflow cavity. These results are used to measure pressure in high-temperature cavities, using a sleeve with a diameter equal to or slightly larger than the diameter of the axial vortex. The sleeve is installed in the vortex chamber, and connects the pressure on its surface to the pressure sensor. The possibility of using a vortex chamber as a damper of pressure fluctuations has been substantiated. The design of the vortex damper and its tests results are presented; these show the possibility of increasing the stabilization time of the outlet pressure more than three-fold. Variants of regulating devices with a vortex chamber, functioning without changing the flow cross-sections, are proposed and the results of their tests are presented. This is achieved either by introducing an obstacle into the chamber cavity or by displacing the axis of the outlet nozzle position.

Numerical Analysis for the Assessment of Factors Influencing the Breakdown of Swirl Flow in a Cylinder Driven by a Rotating End Wall

Finite element solution for the classical problem of swirl flow in a cylinder with a rotating lid has been used to study the characteristic features of the stream-tube and identify the factors contributing to axial vortex breakdown. An increase of rotational Reynolds number has been found to result in (i) a decrease of total flow rate; (ii) an increase of flow rate through the boundary layer over the stationary walls; (iii) an increase of the throat area of the stream-tube, with the upstream axial vortex flow in some cases having a deficit in momentum flux needed to overcome the pressure and viscous forces; and (iv) an increase of distance for the axial flow to sustain deceleration in the diverging passage. Based on the analysis, it is hypothesized that “flow with particles in axial vortex motion having a deficit of momentum flux for axial flow when subjecting to a fluctuating radial force undergoes axial vortex breakdown.” This explanation has been able to justify the disappearance of vortex breakdown at larger Re of laminar regime and the absence of vortex breakdown in small aspect ratio cylinders. We report novel results pertaining to total flow rate and its distribution within the vessel. The momentum flux of axial vortex, a main determinant of bubble breakdown, is found to be governed by the total flow rate, distribution of flow through the boundary layers, and the Reynolds number. The proposed hypothesis has been verified by analyzing two cases, one involving a passive and the other involving an active mechanism for regulating the axial momentum.

Numerical Simulation of Axial Vortex in a Centrifugal Pump as Turbine with S-Blade Impeller

Pump as turbines (PATs) are widely applied for recovering the dissipated energy of high-pressure fluids in several hydraulic energy resources. When a centrifugal pump operates as turbine, the large axial vortex occurs usually within the impeller flow passages. In view of the structure and evolution of the vortex, and its effect on pressure fluctuation and energy conversion of the machine, a PAT with specific-speed 9.1 was analyzed based on detached eddy simulation (DES), and the results showed that vortices generated at the impeller inlet region, and the size and position of detected vortices, were fixed as the impeller rotated. However, the swirling strength of vortex cores changed periodically with double rotational frequency. The influence of vortices on pressure fluctuation of PAT was relatively obvious, deteriorating the operating stability of the machine evidently. In addition, the power loss near impeller inlet region was obviously heavy as the impact of large axial vortices, which was much more serious in low flow rate conditions. The results are helpful to realize the flow field of PAT and are instructive for blade optimization design.