Milan R. Lečić

Original measuring and calibration equipment for investigation of turbulent swirling flow in circular pipe

Modeling of turbulent swirling flow is a contemporary problem in fluid mechanics. In order to make an appropriate modeling it is necessary to have reliable experimental data on instantaneous velocity field. This article presents original equipment for experimental investigation of swirling flow in straight circular pipe. A major role in that equipment plays originally developed and unique hot-wire probe. This probe has high-spatial and temporal resolution, and it can also be used for measuring in a viscous sublayer. Together with detailed description of the probe, the original wind tunnel for hot-wire probes calibration is also presented in this article. The wind tunnel produces the jet with uniform velocity distribution and a very low level of turbulence.

Laser Insight Into the Turbulent Swirl Flow Behind the Axial Flow Fan

Complex experimental study of the turbulent swirl flow behind the axial fan is reported in this paper. Axial fan with nine blades, designed to generate Rankine vortex, was positioned in the circular pipe entrance transparent section with profiled free bell mouth inlet. Two test rigs were built in order to study the turbulent swirl flow generated on the axial fan pressure side in the case of axially unrestricted and restricted swirl flows. One-component laser Doppler anemometry (LDA) and stereo particle image velocimetry (SPIV) were used in the first test rig in the measuring section 3.35D, measured from the test rig inlet. One of the latest measurement techniques, high speed SPIV (HSS PIV), was used for the measurements in the second test rig in the section 2.1D downstream the fan’s trailing edge. Achieved Reynolds numbers in the first test rig are Re = 182600 and 277020, while in the second Re = 186463. Turbulent velocity field non-homogeneity and anisotropy is revealed using the LDA system. Calculated turbulent statistical properties, such as moments of the second and higher orders, reveal complex mechanisms in turbulent swirl flow. It is shown for the used axial fan construction that swirl number has almost constant value for two various duty points generated by changing rotation number. Study of the instant and mean velocity fields obtained using SPIV discovers vortex core dynamics. Obtained percentage of the unique positions of the total velocity minimum are 10% for the first regime, while 11.5% for the second regime in the first test rig. HSS PIV experimental results have also shown the three-dimensionality and non-homogeneity of generated turbulent swirl flow. Experimentally determined and calculated invariant maps revealed three-component isotropic turbulence in the vortex core region.© 2014 ASME

AN EXPERIMENTAL INVESTIGATION AND STATISTICAL ANALYSIS OF TURBULENT SWIRL FLOW IN A STRAIGHT PIPE

This paper presents results of our own velocity field measurements in a straight pipe swirl flow. These studies were conducted using an originally designed hot wire probe. Due to the specially tailored shape of the probe, it was possible to get four measurement points in the viscous sublayer. The time-averaged velocity field and the statistical moments of the second and third order are calculated based on the measured velocity components. Mathematical and physical interpretations of statistical characteristics and structures of turbulent swirl flow in the time domain are presented. On the basis of these results, deeper insight into turbulent transport processes can be obtained, as well as useful conclusions necessary for turbulent swirl flows modeling.

Numerical research of the compressible flow in a vortex tube using OpenFOAM software

The work presented in this paper is dealing with numerical simulation of energy separation mechanism and flow phenomena within a Ranque-Hilsch vortex tube. Simulation of turbulent, compressible, highly swirling flow inside vortex tube is performed using RANS approach, with Favre averaged conservation equations. For turbulence closure, k − e and k − ω SST models are used. It is assumed that the mean flow is axisymmetric, so the 2-D computational domain is used. Compu- tations were performed using open-source CFD software OpenFOAM. All com- pressible solvers available within OpenFOAM were tested, and it was found that most of the solvers cannot predict energy separation. Code of two chosen solvers, which proved as the most robust, is modified in terms of mean energy equation implementation. Newly created solvers predict physically accepted behavior in vortex tube, with good agreement with experimental results. Comparison between performances of solvers is also presented.

Positioning Devices For Measuring Spatial Velocity Correlations in Turbulent Swirl Flow in the Pipe by Hot‐Wire Probes

Measuring spatial correlations of velocity is done by simultaneous measurement of velocity vector in two different measuring points. Usually, the points should be at a very small distance. While performing correlation measurements in turbulent swirling flow in the pipe, it is necessary to have very precise positioning of hot-wire probes, both by angle and distance. In this research, measurements of spatial correlations in such flow field are performed, for two different cases: velocity correlations in two points on different radial distance and in two points on different axial distance, parallel to the pipe axis. For such measurements two original devices for positioning of hot-wire probes are developed. With these devices appropriate angle positioning and radial and axial distance of hot-wire probes are achieved. Cross-correlation diagrams are also given in this article, as an illustration of capabilities of these original devices for hot-wire probes positioning.

Centrifugal pumps' impellers design and digital fabrication

Design of three centrifugal pump impellers is presented in this paper. All impellers are designed in Catia software by Dassault Systems. Impellers have the same outer diameter of 50 mm, but various blade numbers: 5, 6 and 8. In addition, various design techniques are applied. These impellers are followed by the same spiral pump casing. The intention is to study the energy characteristics of the pump impellers, originally designed for various purposes on the same test rig. All three impellers are made on the 3D printing machine - Printrbot Simple. Build volume is 150 mm × 150 mm × 150 mm. Used filament is 1.75 mm PLA/PHA colorFabb 3D printing filament 1.75 mm diameter, standard black, with nozzle 0.4 mm. Print bed is not heated. First tests have shown good impeller durability in operating conditions.

R&D in a Fab Lab: Examples of Paste Extrusion Method

The authors report results of modification performed on the standard, open-source Cartesian style 3D printer and customized hardware (Printrbot Simple Metal) in order to perform paste extrusion with three different materials (hydroxyapatite, clay and chocolate). These results are shown as examples of research and development performed in an informal institution—a fab lab, in connection with formal research institutions. The authors aimed to show how such collaboration of various players in the research community, coupled with multidisciplinary background of participants, produces new and innovative aspects, which is one of the benefits of fab labs.

Conducting architectural experiments: Some new approaches in architectural design

Paradigm shift in architectural design initiated by new technological developments has replaced conventional processes of architectural model design with dynamic transformative ones. This paper examines some of the recent developments in the architectural design through analysis of selected architectural projects and their models. The focus of the paper is the analysis of some new approaches in architectural design through implementation of digital design and novel digital fabrication technologies.