30 research outputs found
CFD Analysis of Impeller Trimming
Impeller trimming is a key impeller modification. It allows the best efficiency point (BEP) to be moved towards the region of lower flowrate and height, thus optimizing pump performance for specific piping systems. The paper deals with prediction of trimming results using CFD methods. Experience shows that modification of the BEP position depends on the trimming method as well as on the pump type and its specific speed. The analysed pump is of diagonal type with a specific speed of nb = 0.168. Its impeller is of a 4-blade design and a spiral casing is used as a volute. Seven cases of trimming are presented (including a non-trimmed original version). The paper compares CFD obtained data and data measured on an experimental stand. Additionally, the approach to CFD analysis, as well as the use of a turbulence model and characteristics of internal pump volume meshing are described
Approach to 3D Unsteady CFD Analysis of a Single-Blade Pump
Single-blade centrifugal pumps are hydraulic machines used in many industrial areas. A unique screw shaped blade enables liquids containing solids and fibrous matters to be pumped. Owing to good pump hydraulic properties on the one hand and unfavourable impeller mechanical properties on the other have single-blade pumps become recently more interesting for researchers regarding the CFD simulations. In this case a conventional CFD approach for multi-blade pumps cannot be applied due to the lack of symmetry of the single-blade impeller. Possible approaches to the CFD simulation of a single-blade impeller in the Ansys Fluent and the Ansys CFX are compared in this paper. A comparison of two CFD meshing tools showed substantial element number decrease of the whole CFD model. This paper presents also the laboratory experiment results of the investigated single-blade pump. The paper describes a new approach to the single-blade CFD simulation through Ansys Fluent which is faster and more user-friendly then the conventional approach
Stall identification methods in centrifugal compressor
The presented paper describes a method for detecting compressor stall precursors in a measured pressure signal using procedures arising from the chaos theory. The experiment was carried out on a scaled-down model of a compressor used in natural gas transportation. It was a single-stage centrifugal compressor with a vane diffuser. The presented method is based on the analysis of an attractor constructed using the time delay method from the pressure signal collected at the compressor outlet flange at a frequency of 25 kHz. Using a parameter called correlation dimension, we identified small changes in the dynamics of the measured signal before the onset of negative stall manifestations. In general, it was found that near the stall curve there were minor disturbances in the flow field in the compressor, due to which the correlation dimension decreased
CFD Analysis of Impeller Trimming
Impeller trimming is a key impeller modification. It allows the best efficiency point (BEP) to be moved towards the region of lower flowrate and height, thus optimizing pump performance for specific piping systems. The paper deals with prediction of trimming results using CFD methods. Experience shows that modification of the BEP position depends on the trimming method as well as on the pump type and its specific speed. The analysed pump is of diagonal type with a specific speed of nb = 0.168. Its impeller is of a 4-blade design and a spiral casing is used as a volute. Seven cases of trimming are presented (including a non-trimmed original version). The paper compares CFD obtained data and data measured on an experimental stand. Additionally, the approach to CFD analysis, as well as the use of a turbulence model and characteristics of internal pump volume meshing are described
Visualization of cavitating micro jets
The paper deals with one experimental set up integrated for research of the cavitating micro flows, which is incipient behind the micro channel or micro discharge nozzle outlet port. Experimental system is integrated from three major systems: hydraulic circuit with installed discharge nozzle (or micro channel), subsystem for data acquisition and data processing (DAQ system) and vision system compound of high speed video camera and pulse light source with highfrequency repetition. First few results of experiments (parameters such as inlet pressure, downstream pressure were changed) is also discussed.
Observation of development of cavitation damage
The paper presents a method developed and applied for observation of cavitation effects on material of different properties. It is intended for observation of cavitation effects of microorifices on selected materials. In the paper are presented some results obtained in our institute by applying of presented method
Disintegration of materials by cavitating microjets
In the paper is presented an investigation of material disintegration by cavitating microjets. Cavitating microjet develops behind the micro-orifice at high flow speeds, when local pressure drop initiates a cavitation phenomenon. Described is a method and presented are selected results of experiments. Experiments were carried out with 2 micro-orifices at different flow conditions (cavitation number, distance between sample and micro-orifice). Experiments are based on flow visualisation as well as on a character of material displacement
Experimental system for measuring the force load of a single blade pump
Precise evaluation and anticipation of the radial and axial force loads acting on the impeller of a spiral casing pump are essential to ensure that the pump operates efficiently and dependably. This study presents an experimental system for measuring the force load of a single blade pump and explores the fluid mechanics involved in its operation. The experimental system consists of a strain gauge and a data acquisition system, which measures the force load on the blade as the pump rotates. In addition, our investigation delves into various approaches for measuring radial force loads, which include the evaluation of reaction forces on bearings. For the case of experimental measurement of the radial and axial force in the pump bearings, it is necessary to make some design modifications on the pump body. The measurement methodology is based on the principle of a “relaxed” shaft that performs a so-called spherical motion around the rotation axis during pump operation
Effect of Impeller Size on the Performance of a Single Blade Pump
Changing the impeller diameter is a frequently used method for adjusting pump performance parameters. In the case of conventional multi-blade impellers, this is done by reducing the diameter on the machine tool to the prescribed shape. The other dimensions of the pump (diffuser, inlet) remain unchanged. This method is called trimming. The article deals with the diameter reduction and subsequent modification of the performance parameters of a single blade pump. These pumps are characterized by certain specific features. First of all, it is an unsymmetrical impeller that must be both statically and dynamically balanced. This plays an essential role in the whole modification process. Research results obtained on a pump with an impeller diameter of 138 mm are presented. The change in diameter was monitored on a total of 3 impellers. Experiments were carried out in the laboratory of hydraulic machinery. The results were verified by CFD calculations.
Research background: The article concerns the modification of impellers of single blade pumps. The effects of diameter modifications on multi-blade pumps are currently known. However, these have symmetrical impellers and can therefore be changed without restriction. For asymmetric (single blade) impellers, the problem is more complex as additional mass must be added to provide static and dynamic balance.
Purpose of the article: The aim is to determine the nature of the change in performance parameters when the output diameter is changed. The results of the research can be applied in the prediction of the change in the operating point and the creation of tombstone charts.
Methods: Two kinds of methods were used in the research: experiment and CFD calculation. A total of 4 impeller sizes were investigated.
Findings & Value added: The results of the paper can be divided into two areas. In the experimental area, a device was designed to measure the characteristics of single blade pumps. Four impellers were manufactured and tested. In the area of CFD calculations, simulations of the hydraulic parameters around the best efficiency point (BEP) were performed. The calculation results were verified by experiment. The nature of the change of the BEP when the diameter of the impeller changes up to 87.9 % was found
Character of the cavitation erosion on selected metallic materials
It's well known, that the imploding cavitation bubbles causes the damage on the solid surfaces. This process is then dangerous for the mechanical parts of the hydraulic machines. Proposed article dealing with the analysis of the type of the damage caused by the cavitation erosion according to the selected metallic material of the specimen. As is shown in the article, the type of the damage has a realtion to the hydraulic parameters of the flow (velocity, cavitation number). The optical and weight measerument methods will be used for the anlysis