Effects of an Impeller Rim and Radial Clearance on Energy Characteristics of an Axial Pump

The results of numerical and experimental research conducted in the Laboratory for Hydraulic Machinery Construction of Peter the Great St. Petersburg Polytechnic University are presented. The research is aimed at studying the effects of an impeller radial clearance and rim on the energy characteristic of low-pressure axial pumps of the specific speed ns≈600. It is shown that these design features of a flow duct have significant effects on stage parameters, and they have to be accounted for when verifying design and experimental characteristics of axial pumps.

Irrigation pumping stations according to the hydraulic and operational indicators of pumping units

The paper presents the conditions and the degree of reduction of water supply and pressure of pumping stations (PS) depending on the hydraulic resistance of the water-supply channels and structures of the PS and other various factors. And also, the results of studies of the hydraulic and operational modes of water-supplying machine channels and structures of irrigation pumping stations are presented. Analyzing the operating conditions of the pumping units, it was found that the reasons for the decrease in their operating parameters are the following: a) an increase in the hydraulic resistance of the suction line due to sediment deposition in the intake chamber, as well as due to siltation and clogging of the PS suction pipeline; b) an increase in hydraulic resistance due to the accumulation of air at elevated points of the pressure pipeline, in particular, on the crest of the siphon outlet of the PS; c) a decrease in the hydraulic efficiency of pumping units due to an increase in the surface roughness of the parts of the flow path, it due to the effect of solid abrasive particles entering through the suction line of the PS. Also, the work presents the results of complex laboratory and field studies to study the intensity of wear of the elements of the flow path of centrifugal and axial pumps. The alternating pulsating load leads to an increase in the force of interaction of the hydroabrasive flow with the surface of the chamber and increases its wear by 10%, and also reduces the productivity of the pumping unit to 9%.

Theoretical Analyses of the Number of Backflow Vortices on an Axial Pump or Compressor

This paper presents theoretical analyses of flow fields on an axial pump or compressor, where the main flow enters from one side of the cylindrical casing, whereas an axially reverse and tangentially whirling flow enters from the tip clearance between the casing and the impeller, which sucks in the mixed flow. In this flow field, several secondary vortices exist in the mixing zone across the contact surface between the main and the axially reverse tangentially whirling flow. This type of secondary vortex is called a “backflow vortex.” The backflow vortices are tornado-like, parallel to the casing axis, and periodically distributed on the contact surface; they revolve around the casing axis and rotate around themselves. Regarding the backflow vortices, the relationships between their number (N), revolving diameter (d), revolving angular velocity (ω), and the ratio of the forced vortex region to the distance between the secondary-vortex center and the cylindrical wall (f) were all theoretically investigated. The five major findings are as follows: First, between d, ω, N, and f, any parameter can be determined if the other three are specified. Second, ω decreases, N increases, or f increases when d is increased and the other two are fixed. Third, d decreases, N increases, or f increases when ω is increased and the other two are fixed. Fourth, d increases, ω increases, or f decreases when N is increased and the other two are fixed. Fifth, d increases, ω increases, or N decreases when f is increased and the other two are fixed. To validate these theoretical results, “backflow vortex cavitation,” which occurs around the center of the backflow vortices on a rotating inducer as a representative of axial pumps or compressors, was observed. The backflow vortex cavitation is visible; therefore, d, ω, and N become quantitatively measurable. The test inducer was a triple-threaded helical inducer with a diameter of 65.3 mm and a rotational speed range of 3000–6000 rpm. It was experimentally confirmed that the proposed theoretical analysis is true.