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

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

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

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

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

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.

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

Multi-Exposure PIV Measurements of Velocity Fields in Sprays

This paper presents an approach to the use of the PIV method in the diagnosis of sprays generated by an effervescent atomiser. Due to the different density of the liquid phase depending on the distance from the nozzle, problems arise with the correct exposure of images for PIV analysis. The aim of the authors of this paper is to outline the possibility of solving this problem by composing a velocity field from partial measurements. To meet the objectives of the paper, in-house PIV equipment (hardware and software) was used rather than a commercial setup. This allowed for easier handling of the measured data and more sophisticated post-processing than offered by commercial products. It is clear from the results presented that, despite the fundamental differences in the optical properties of the spray particles, it is possible to obtain a velocity field from the discharge zone to the spray region with fine droplets. Moreover, it is possible to combine velocity measurements in the spray cone with measurements in the surrounding environment. Research background: Spray is an environment with an abundance of tracers for PIV analysis (droplets), but their density, size and shape vary dramatically with distance from the nozzle. The use of PIV can therefore be challenging due to the demands of this method for correct image exposure. Purpose of the article: Introduction of the application of the PIV method for environments with variable density and size of tracer particles Methods: PIV, image processing. Findings & Value added: By taking an appropriate approach to acquiring the source PIV images, it is possible to obtain information about the velocities throughout the spray cone as well as in the surrounding environment. The application of the proposed method requires a sufficiently large source data set (images) and sophisticated postprocessing. However, as a result, it is possible to obtain an overall view of the velocity field in the spray cone starting from the area behind the nozzle to the fine droplet region

Vizualization of the cavitating jet using flashlamp for illumination

The contribution deals with the ways of the illumination of the cavitating jet for the purposes of the visualization. The cavitation is induced by the fluid flow through the orifice with the diameter of 0,3mm. Region of the cavitating jet is illuminated by a different light sources. Goal of this paper is to compare the quality and the informative value of the obtained visual data. In addition, complicated structure of the cavitating jet is also shown and described