Hydrodynamic phenomena in centrifugal vortex pump

Konstrukcija i određivanje radnih karakteristika pumpi je i dalje složen zadatak, prvenstveno zbog velikog broja slobodnih geometrijskih parametara čiji se utjecaj ne može direktno procijeniti. Značajna cijena koštanja konstruiranja pumpi na temelju eksperimentalnih istraživanja, tj. mjerenjima na prototipovima čini računalne simulacije temeljene na računalnoj mehanici fluida (engl. Computational fluid dynamics - CFD) najprihvatljivijim alatom pri konstruiranju i analizi radnih karakteristika pumpi. Međutim, nestacionarne pojave pri međudjelovanju rotora i statora, te nestabilnosti strujanja i dalje nužno zahtijevaju validaciju i verifikaciju dobivenih rezultata eksperimentalnim putem. Istraživanje energetske pretvorbe u centrifugalno vrtložnoj pumpi u ovom radu je provedeno numeričkim simulacijama strujanja u centrifugalnoj pumpi, centrifugalno vrtložnoj pumpi i vrtložnom dijelu centrifugalno vrtložne pumpe, te mjerenjima relevantnih parametara koji opisuju radne karakteristike pumpi na njihovim fizikalnim modelima. Rezultati mjerenja poslužili su kao eksperimentalna validacija numeričkih simulacija, ali i obrnuto, vizualizacija strujanja proizašla iz numeričke simulacije korištena je za interpretaciju mjerenja. Validacija numeričkog modela provedena je usporedbom dobivenih integralnih veličina, (protoka, visine dobave i snage) s izmjerenima na istovjetnim fizikalnim modelima. Također je provedena usporedba dobivenih veličina kod centrifugalne, centrifugalno vrtložne pumpe i vrtložnog dijela u cilju njihove usporedbe. Za potrebe provođenja eksperimentalnih istraživanja, u Laboratoriju za hidrodinamiku i hidrauličke strojeve Fakulteta strojarstva i brodogradnje u Zagrebu, izrađeni su fizikalni modeli centrifugalne i centrifugalno vrtložne pumpe koji odgovaraju numeričkim te eksperimentalna linija s pripadajućom opremom koja je omogućila promjenu broja okretaja, odabir radne točke te mjerenje trenutnog protoka, prirasta tlaka i snage pogonskog elektromotora. Numerička simulacija nestacionarnog strujanja u centrifugalnoj pumpi i centrifugalno vrtložnoj pumpi provedena je korištenjem aplikacijskog komercijalnog programskog paketa ANSYS Fluent za računalnu dinamiku fluida koji se temelji na metodi konačnih volumena. IV Provedena istraživanja su pridonijela pojašnjenju mehanizama energetske pretvorbe u centrifugalno vrtložnoj pumpi te potvrdila povoljni utjecaj vrtložnog vijenca na karakteristike iste (protok, tlak, iskoristivost, kavitacijska karakteristika).The design and performance prediction of pumps is still a complex task, mainly due to a large number of free geometrical parameters whose influence cannot be directly evaluated. The significant financial cost of pump design by trial and error methods and the cost of experimental prototype testing, renders the computational fluid dynamics (CFD computer simulation) as the most acceptable tool in the design and performance analysis of pumps. However, unsteady phenomena in the form of interaction of rotor and stator and other flow instabilities continue to make accurate prediction of the pump characteristics a difficult and time-consuming task, which still requires validation and verification of the experimentally obtained results. In this paper the research of the energy transformations in centrifugal vortex pump has been performed by numerical simulation of flow in centrifugal pumps, centrifugal vortex pumps and vortex part of centrifugal vortex pump, as well as by the measurements of relevant parameters that describe the performance of pumps on their physical models. The results of experimental measurements served primarily as experimental validation of numerical simulation, and vice versa, the visualization of the flow arising from numerical simulations was used for the interpretation of measurements. The validation of the numerical model was conducted by comparing the integrated quantities, flow rate, the head and the power consumption with those obtained by measurements on identical physical models. Also, a comparison of the obtained physical values was conducted with the aim of making a conclusion about the diversity of integral parameters of centrifugal pumps, centrifugal vortex pump and the vortex part of the centrifugal vortex part. During the preparation of this research, at the Laboratory for Hydrodynamics and hydraulic machinery, Faculty of Mechanical Engineering and Naval Architecture University of Zagreb, physical models of centrifugal pump and centrifugal vortex pump were made, that correspond to numerical models and the experimental line with the respective equipment that allowed the change of angular velocity, setting of the working point and measuring of current flow, increment of pressure and propulsion power. The numerical simulation of unsteady flow in centrifugal pumps and centrifugal vortex pumps VI were conducted using commercial software package ANSYS Fluent for Computational fluid dynamics which is based on the finite volume method. The research results have contributed to clarify the mechanisms of energy conversion in a centrifugal vortex pump and confirmed the favorable impact of a vortex ring on the pump characteristics (flow, pressure, efficiency, cavitation characteristics)