Hydrodynamic Analysis of Fluid Obstruction Around Different Geometric Bodies

The aim of this paper is to conduct a hydrodynamic analysis of fluid flow around different geometric bodies on the laboratory physical model HM 133 of the Gunt Company from Hamburg and to show the formation of boundary layer and separation points on the observed bodies. The paper covers the field of real fluid dynamics which includes a description of laminar and turbulent flow together with a Reynolds number. A detailed representation of the boundary layer, its characteristics, and its structure are included. The body models in the paper used on the HM 133 physical model were an oblong straight body and cylindrical bodies with 6 mm, 12 mm, 18 mm, and 24 mm in diameter. The research was conducted in the Hydrotechnical Laboratory of the Faculty of Civil Engineering, University of Rijeka. Hydrodynamic analyses were made based on the tested body models on the physical model HM 133 together with the analyses on the numerical models performed using the ANSYS Fluent software

Cavitation Instabilities at the Entrance Pipe of Centrifugal Pump

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Physical Model of Forming the Boundary Layer

U radu se razmatraju temeljna načela za formiranje graničnog sloja kod ravninskih (2D) i prostornih (3D) objekata te je dat opis načina njegova formiranja pomoću fizikalnih modela HM 133 i HM 152 (tvrtke GUNT), koji su sastavni dio hidrotehničkog laboratorija Građevinskog fakulteta Sveučilišta u Rijeci. U prvom dijelu rada definirane su osnove gibanja tekućine putem Lagrangeovog i Eulerovog pristupa. Kroz tekstualne formulacije i grafičke prikaze objašnjeno je značenje trajektorija, strujnica, vektora brzina i ubrzanja, kao i njihova povezanost. Također je opisan pojam kutne deformacije koju trpi čestica tekućine uslijed gibanja. U nastavku rada dat je opis osnovnih teorijskih pretpostavki o formiranju graničnog sloja te triju vrsta tečenja obzirom na njegovo formiranje. Tu je i dio koji upućuje na važnost hrapavosti podloge i gradijenta tlaka na formiranje graničnog sloja. Zatim su prikazane zakonitosti utvrđene za sustave otvorenih kanala jer njima odgovaraju uvjeti na korištenim fizikalnim modelima. Nadalje su opisani principi rada dva navedena fizikalna modela, način pripreme samih eksperimentanih ispitivanja te je provedena analiza opstrujavanja fluida na pojedinim ravninskim, 2D objektima (kružnog, pravokutnog i aerofilnog oblika) i prostornim, 3D objektima (cilindričnog i aerodinamičkog oblika).The paper deals with the basic principles of forming the boundary layer in linear (2D) and spatial (3D) objects, along with the description and manner of their forming using physical models GUNT HM 133 and GUNT HM 152, which are an integral part of the hydro-technical laboratory of the Faculty of Civil Engineering, University in Rijeka. Firstly, the paper defines motion of liquid basics with Lagrange and Euler approach. The meaning of trajectories, streamlines, velocity vectors and acceleration, as well as their interdependence, were explained using textual formulations and graphic displays. The concept of angular deformities, suffered by particles of fluid due to movement, were also described. Furthermore, the paper describes the basic theoretical assumptions regarding formation of a boundary layer and three types of flow due to their formation. A part of paper also points to the importance of surface roughness and pressure gradient regarding the formation of the boundary layer. The legalitie, deremined for open channel systems, are also shown, because they correspond to the conditions of the applied physical modes. The paper describes the principles of work for the two stated physical models, the manner of preparing the experimental tests, and the conducted hydrodynamic analysis of fluid circulation on certain linear 2D structures (of circular, rectangular and aerofil shape) and spatial 3D structures (of cylindrical and aerodynamic shape)

Experimental Investigation of Friction and Resistence Coefficients in Pipe System under Pressure

U radu je provedeno eksperimentalno određivanje linijskih i lokalnih gubitaka, odnosno koeficijenata linijskih i lokalnih gubitaka na nekoliko karakterističnih fazonskih komada unutar cijevnog sustava pod tlakom. U svrhu izračuna navedenih koeficijenata, dane su mjerodavne formulacije za njihovo određivanje. U sklopu rada na fizikalnom modelu GUNT HM 150 u sklopu Praktikuma hidrotehničkog laboratorija Građevinskog fakulteta Sveučilišta u Rijeci, provedena su tri osnovna eksperimentalna mjerenja: proračun određivanja lokalnih gubitaka na cijevnom koljenu (pod kutom od 45° i 90°), hidraulička analiza uslijed promjene poprečnog presjeka cijevi (postepeno suženje i proširenje cijevi) te hidraulička analiza uslijed grananja cijevne dionice (račvasti dio cijevnog sustava). Na kraju rada dani su zaključci koji proizlaze iz provedenih eksperimentalnih pokusa, kao i smjernice za buduća dodatna ispitivanja lokalnih i linijskih gubitaka na danom fizikalnom modelu.In this paper experimental investigation of major and minor hydraulic losses, ie the friction and resistent coefficients was performed on several characteristic fittings within the pressurized pipe system. For the purpose of calculating these coefficients, relevant formulas have been given for their determination. Within the work on the physical model GUNT HM 150 as a part of the Practicum Hydro-technical laboratory of the Faculty of Civil Engineering in Rijeka, three basic experimental measurements were conducted: calculation for defining minor hydraulic losses on the pipe joint (under an angle of 45° and 90°), hydraulic analysis from the changes of the cross section of the pipe (gradual narrowing and widening of the pipes), and hydraulic analysis from the branching of the pipe legs (branched part of the pipe system). At the end of the paper, conclusions were given based on the conducted experimental tests, as well as guidelines for future additional tests of minor and major hydraulic losses on the given physical model

Primerjava kavitacijskih modelov za numerično napoved kavitacije na hidrodinamičnem profilu

In this paper, four different cavitation models were compared for predicting cavitation around a hydrofoil. A blocked structured mesh was created in ICEM CFD. Steady-state 2D simulations were performed in Ansys CFX. For all cases, the SST turbulence model with Reboud\u27s correction was used. For Zwart and Schnerr cavitation models, the recommended values were used for the empirical coefficients. For the full cavitation model and Kunz cavitation model, values for the empirical coefficients were determined as the recommended values did not provide satisfactory results. For the full cavitation model, the effect of non-condensable gases was neglected. For all the above-mentioned cavitation models, the pressure coefficient distribution was compared to experimental results from the literature.V prispevku je narejena primerjava med štirimi kavitacijskimi modeli pri numerični napovedi kavitacije na hidrodinamičnem profilu. V ICEM CFD je bila izdelana blokovna strukturirana mreža. V Ansys CFX so se izvedle 2D stacionarne simulacije. Za vse simulacije je bil uporabljen SST turbulentni model s korekcijo, ki jo je uvedel Reboud. Za kavitacijska modela Zwart in Schnerr smo uporabili privzete vrednosti empirični koeficientov. Za full cavitation model in Kunzov kavitacijski model smo vrednosti koeficientov določili sami, saj privzete vrednosti niso dale zadovoljivih rezultatov. Za vse štiri zgoraj omenjene kavitacijske modele smo primerjali porazdelitev tlačnega koeficienta z eksperimentalnimi rezultati iz literature

Napoved kavitacijske erozije in erozije delcev v radialno divergentni testni sekciji

The 3D unsteady, cavitating, particle-laden flow through a radial divergent test section was simulated with the homogeneous mixture model and Discrete Phase Model (DPM) within the commercial CFD code ANSYS Fluent. For turbulence, a RANS approach was adopted with the Reboud’s correction of turbulent viscosity in the k-ω SST model. Cavitation erosion was predicted with the Schenke-Melissaris-Terwisga (SMT) model, while particle erosion was predicted with the Det Norske Veritas (DNV) model. Two distinct erosion zones were identified, one for pure cavitation erosion and one for pure particle erosion. The occurrence of the pure particle erosion zone downstream of the cavitation erosion zone was analysed. By observing the streamlines downstream of the cavitation structures, it was found that vortices form in the flow and redirect the particles towards the wall, causing a pure particle erosion zone on the wall. Particles under consideration in this study were not found to alter the flow to the extent that the cavitation erosion zone would be significantly altered compared with the results without solid particles which are reported in the literature.3D nestacionaren, kavitirajoč tok z delci skozi radialno divergentno testno sekcijo je bil simuliran z modelom homogene zmesi in modelom diskretne faze (DPM) s komercialno RDT kodo ANSYS Fluent. Turbulenca je modelirana po pristopu RANS z Reboudovim popravkom turbulentne viskoznosti v modelu k-ω SST. Izvedeni sta bili napoved kavitacijske erozije z modelom Schenke-Melissaris-Terwisga (SMT) in napoved erozije zaradi delcev z modelom Det Norske Veritas (DNV). Prepoznani sta bili dve različni erozijski coni, ena za zgolj kavitacijsko erozijo in ena za erozijo zgolj zaradi delcev. Analiziran je bil pojav cone čiste erozije zaradi delcev dolvodno od cone kavitacijske erozije. Z opazovanjem tokovnic dolvodno od kavitacijskih struktur je bilo ugotovljeno, da se v toku oblikujejo vrtinci in preusmerjajo delce proti steni, kar povzroča na steni cono erozije zgolj zaradi delcev. Ugotovljeno je bilo, da delci, obravnavani v tej študiji, ne spreminjajo toka do te mere, da bi se območje kavitacijske erozije znatno spremenilo v primerjavi z rezultati brez trdnih delcev, o katerih poroča literatura

Prerotation flow measurement

Different measuring methods relating to the prerotation flow in the entrance pipe of radial pumps are analyzed. The appearance of the prerotation flow is a result of the complicated fluid flow model, which appears as a consequence of the pump operating out of design limits and reduces pump efficiency. The goal of this contribution is in estimating the best measuring method, taking into account the inconvenience of conventional hot-wire and laser-Doppler anemometry. Therefore, two measuring systems - multiblade (ASB) and single blade (ASSB) anemometer - are introduced, analyzed and compared. The advantages of the introduced measuring system -ASB- are in its simple construction and simple use and its low price. The direction and swirl flow intensity in the entrance pipe of radial pumps and fans could be measured using this method

The driving mechanisms of the cavitation swirl in the entrance pipe of a radial pump

V prispevku je podana analiza gonilnih mehanizmov in tlačnih utripanj povezanih s pojavom kavitacijskega vrtinca v vstopnem vodu radialne črpalke. Kavitacijski vrtinec je rezultat interakcije številnih zapletenih sekundarnih tokovnih pojavov, ki nastopijo kot posledica obratovanja s podoptimalnimi pretoki v kavitacijskem obratovalnem režimu. Izvedene in predstavljene so tudi meritve tlačnih utripanj v vstopnem vodu radialne črpalke na različnih razdaljah od rotorskega ustja na sklenjeni kavitacijski merilni progi. Meritve so izvedene pri različnih vrtilnih hitrostih in različnih tlakih nad spodnjo vodno gladino. Podani so tudi rezultat frekvenčne analize posnetih tlačnih utripanj.Analyses are given of the driving mechanisms and pressure pulsations relating to the cavitation swirl in the entrance pipe of a radial pumpe. The appearance of cavitation swirl is a result of a complicated secondary flow interaction, which appears as a consequence of the pump operating at small, under-optimum capacities in the cavitation operating regime. Results of the flow pressure pulsation measurements in the entrance pipe of the radial pump are reported. These measurements were made at different distances from the impeller eye, in the upstream direction at the closed cavitation measuring test ring with the pump operating at different impeller speeds and at different values of gas (air) pressure over the lower liquid (water) position. Results are also given for the frequency analyses of the measured flow pressure