Aleksandar S. Ćoćić

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.

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.

COMPARISON OF DIFFERENT CFD SOFTWARE PERFORMANCES IN THE CASE OF AN INCOMPRESSIBLE AIR FLOW THROUGH A STRAIGHT CONICAL DIFFUSER

Numerical flow simulations have been carried out in order to analyze the possibilities of numerical prediction of a steady-state incompressible air flow through a conical diffuser named Azad diffuser. The spreading angle of this diffuser is 8o and it has cylindrical parts of the constant diameter in the inlet and outlet flow zones. Numerical analysis has been performed by the use of the standard k-e turbulence model. The simulations have been performed using the Ansys CFX and the OpenFOAM software for cases of 2-D and 3-D computational domains. In both cases a fully developed turbulent flow at the inlet section of diffuser is present. The numerical flow simulation in a 2-D computational domain has been performed under the assumption of an axisymmetric flow in the diffuser. Numerically obtained results have been compared with experimental data. Results obtained with these two softwares have also been mutually compared. At the end the results obtained by CFD for the cases of 2-D and 3-D computational domains have been mutually compared, and the advantages and disadvantages of performing numerical simulations under the assumption of an axisymmetric flow in the diffuser have been analyzed.