The aim of this study is to examine different blowing configurations of
 multiple swirling jets for use it in terminal units of ventilation
 applications. The influence of several parameters such as the inclined vanes
 of diffuser and the sense of rotation of the single or multiple swirling
 jets, their number and their arrangement on the flow resulting dynamically
 and thermally is experimentally investigated. Flow rate was adjusted at
 Reynolds numbers, Re0, ranging from 104 to 30.103. The current study is
 carried out under uniform heat flux condition for each diffuser at Reynolds
 number of 30.103, the air being the working fluid. Experiences concerning the
 fusion of several jets show that the resulting jet is clearly more
 homogenized under swirling influence. The findings of this study show that
 the gap between the jets and their sense of rotation relative to the central
 jet, affects the quality of the homogenization of ambiance. Among the studied
 different configuration, the one which consists of a swirling central jet
 controlling the behavior of six swirling jets in counter-rotation is shown to
 be the most effective in terms of thermal destratification.

/pdf/improvement-of-thermal-homogenization-using-multiple-1ydx327veu.pdf

Improvement of thermal homogenization using multiple swirling jets

Laser-Doppler anemometry application in measurements of the 3-D swirl turbulent flow velocity in the cylindrical pipe, behind the axial fan, have been analysed. This paper presents a brief overview of uncertainty sources in the laser-Doppler anemometry measurements. Special attention is paid to estimation of laser-Doppler anemometry measuring volume positioning in cylindrical pipe flow due to optical aberrations, caused by the pipe wall curvature. The hypothesis, that in the central part of the pipe (r/R < 0.6) exists a small, or negligible pipe wall influence on laser-Doppler anemometry measuring position, is investigate. The required corrections, for measurements of axial, tangential, and radial velocity components such: shift of measuring volume and its orientation are analysed and determined for used test rig and for some other pipe geometries.

/pdf/estimation-of-laser-doppler-anemometry-measuring-volume-3whzbp4g7g.pdf

Estimation of laser-Doppler anemometry measuring volume displacement in cylindrical pipe flow

This review paper provides data about research activities at the School of the turbulent swirling flow at the Faculty of Mechanical Engineering, University of Belgrade, conducted in the period 1941 up to date. An overview is provided of the main directions in this research area. First papers dealt with the turbulent swirling flow in hydraulic turbines to be continued by the experimental and analytical approaches on the axial fans pressure side. The complexity of 3-D, non-homogeneous, anisotropic turbulent velocity fields required complex experimental and theoretical approach, associated with the complex numerical procedures. Analytical approaches, complex statistical analyses and experimental methods and afterwards CFD employed in the research are presented in this paper. The 150 scientific papers, numerous diploma works, several master of science (magister) theses, six Ph. D. theses and two in progress, 40 researchers, national and international projects are the facts about the School. Scientific references are chronologically presented. Numerous abstracts from scientific conferences, presentations, projects with industry and lectures are not given here.

/pdf/the-school-of-the-turbulent-swirling-flow-at-the-faculty-of-3v18ov7qco.pdf

The school of the turbulent swirling flow at the Faculty of Mechanical Engineering University of Belgrade

To investigate traffic tunnel ventilation flows, a scaled model of a traffic
 tunnel with longitudinal ventilation system based on ducted fans is used.
 Flows in tunnels are influenced by tunnel geometry, fan characteristics,
 ventilation operation scenario, vehicle traffic, atmospheric factors, etc. To
 analyze flow fields of tunnels in detail, knowledge of tunnel jet-fan
 properties and turbulent flow characteristics at the fan exit are required,
 and can be used as input data for CFD boundary conditions of tunnel flow
 computation. For this purpose experimental measurements were done using the
 hot wire anemometry technique. The obtained results, trough ensemble-averaged
 and time averaged profiles of all velocity components, turbulence intensity,
 turbulent kinetic energy, integral flow length scales, available Reynolds
 stresses, Turbulent kinetic energy production rates and the fan thrust
 performance, are presented. These data allow us to analyze in more detail the
 influence of fan flow on energy and pollutant removal efficiencies of the
 tunnel ventilation and to evaluate accuracy of CFD studies on fan
 improvements.

/pdf/experimental-determination-of-tunnel-ventilation-axial-3vxhn8glcj.pdf

Experimental determination of tunnel ventilation axial ducted fan performance

Experimental research of the turbulent swirl flow in the pipe behind the axial fan impeller is presented in this paper. Axial fan is inbuilt without guide vanes in the installation with a free inlet and ducted outlet, like it is widely used in the ventilation systems. One-component laser Doppler anemometry and stereo particle image velocimetry (SPIV) are used in two measuring sections on the fan pressure side and for three fan rotation numbers. Non-dimensional axial velocity profile is not significantly transformed downstream, while the circumferential is, although it preserves its character. Turbulence level is the highest in the vortex core in both measuring sections for all velocities. It increases downstream in the vortex core zone and decreases in the main flow region. Determined skewness and flatness factors point out the intermittent character of the generated turbulent swirl flow, as well as the existence of the organized coherent structure. Correlation curves indicate various dynamics of fluctuating circumferential velocity fields in measuring points. The Rankine vortex structure of the turbulent swirl flow is also revealed by the SPIV measurements. Analysis shows more dominant vortex core dynamics in the downstream section. Studied flow is characterized by extensive mass, momentum and energy transfer.

/pdf/study-of-the-turbulent-swirl-flow-in-the-pipe-behind-the-16bvx7upqt.pdf

Study of the turbulent swirl flow in the pipe behind the axial fan impeller

Geometry analysis of the axial fan impeller, experimentally obtained operating characteristics and experimental investigations of the turbulent swirl flow generated behind the impeller are presented in this paper. Formerly designed and manufactured, axial fan impeller blade geometry (originally designed by Prof. Dr- Ing. Z. Protic † ) has been digitized using a three-dimensional scanner. In parallel, the same impeller has been modeled by beta version software for modeling axial turbomachines, based on modified classical calculation. These results were compared. Afterwards, the axial fan operating characteristics were measured on the standardized test rig in the Laboratory for Hydraulic Machinery and Energy Systems, Faculty of Mechanical Engineering, University of Belgrade. Optimum blade impeller position was determined on the basis of these results. Afterwards, impeller with angle 22, without outlet vanes, was positioned in a circular pipe. Rotational speed has been varied in the range from 500 till 2500 rpm. Reynolds numbers generated in this way, calculated for axial velocity component, was in the range from 0.68·10 5 till 2.5·10 5 . Laser Doppler anemometry measurements and stereo particle image velocimetry measurements of the three-dimensional velocity field in the swirl turbulent fluid flow behind the axial fan have been performed for each regime. Obtained results point out extraordinary complexity of the structure of generated three-dimensional turbulent velocity fields.

/pdf/novel-methods-for-axial-fan-impeller-geometry-analysis-and-u9yx1y3u2p.pdf

Novel methods for axial fan impeller geometry analysis and experimental investigations of the generated swirl turbulent flow

Fluid flow in curved channels with various cross-sections, as a common problem in theoretical and applied fluid mechanics, is a very complex and quite undiscovered phenomenon. Defining the optimum shape of the fluid flow boundaries, which would ensure minimum undesirable phenomena, like "dead water" zones, unsteady fluid flow, etc., is one of the crucial hydraulic engineering’s task. Method of kinetic balance is described and used for this purpose, what is illustrated with few examples. .

/pdf/fluid-boundaries-shaping-using-the-method-of-kinetic-balance-9b7i8a8j93.pdf

Fluid boundaries shaping using the method of kinetic balance

a Institute of Nuclear Techniques, Budapest University of Technology and Economics, Budapest, Hungary b Department of Thermohydraulics, Centre for Energy Research, Hungarian Academy of Sciences, Budapest, Hungary c Energy Engineering Department, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, Budapest, Hungary d Faculty of Mechanical Engineering, University of Belgrade, Belgrade, Serbia

/pdf/study-and-analysis-of-the-cavitating-and-non-cavitating-jets-rdtgedk0rq.pdf

S Milos Nedeljkovic

Papers

Novel methods for axial fan impeller geometry analysis and experimental investigations of the generated swirl turbulent flow

Fluid boundaries shaping using the method of kinetic balance

Study and analysis of the cavitating and non-cavitating jets - Part one: Parameters controlling force, power and the jet behavior