Mehdi Nazarinia

Experimental vortex breakdown topology in a cylinder with a free surface

The free surface flow in a circular cylinder driven by a rotating bottom disk is studied experimentally using particle image velocimetry. Results are compared with computational results assuming a stress-free surface. A dye visualization study by Spohn et al. [“Observations of vortex breakdown in an open cylindrical container with a rotating bottom,” Exp. Fluids 14, 70 (1993)], as well as several numerical computations, has found a range of different vortex breakdown structures in this flow. We confirm the existence of a transition where the top of the breakdown bubble crosses from the axis to the surface, which has previously only been found numerically. We employ a technique by Brons et al. [“Topology of vortex breakdown bubbles in a cylinder with rotating bottom and free surface,” J. Fluid Mech. 428, 133 (2001)] to find the corresponding bifurcation curve in the parameter plane, which has hitherto only been used on numerical data. The bifurcation curve located here agrees well with previous numerical s...

Flow behind a cylinder forced by a combination of oscillatory translational and rotational motions

The flow behind a cylinder undergoing forced combined oscillatory motion has been studied. The motion consists of two independent oscillations: cross-stream translation and rotation. Previous studies have extensively investigated the effect of these motions individually on cylinder wakes; however, the investigation of their combined effect is new. The motivation lies in its application to vortex-induced vibration and its suppression and to biomimetic motion. The focus is on the effect of the phase difference between the two motions. The results show that there is an unexpected loss of synchronization of the wake for a finite range of phase differences.

The three-dimensional wake of a cylinder undergoing a combination of translational and rotational oscillation in a quiescent fluid

Previous two-dimensional numerical studies have shown that a circular cylinder undergoing both oscillatory rotational and translational motions can generate thrust so that it will actually self-propel through a stationary fluid. Although a cylinder undergoing a single oscillation has been thoroughly studied, the combination of the two oscillations has not received much attention until now. The current research reported here extends the numerical study of Blackburn et al. [Phys. Fluids 11, L4 (1999)] both experimentally and numerically, recording detailed vorticity fields in the wake and using these to elucidate the underlying physics, examining the three-dimensional wake development experimentally, and determining the three-dimensional stability of the wake through Floquet stability analysis. Experiments conducted in the laboratory are presented for a given parameter range, confirming the early results from Blackburn et al. [Phys. Fluids 11, L4 (1999)]. In particular, we confirm the thrust generation abil...

Optimisation of Boat-Tails for Heavy Vehicles

Boat-tails offer significant promise in reducing long haul heavy vehicle aerodynamic drag, and hence fuel consumption and greenhouse gas emissions. This paper presents results from a basic numerical and experimental investigation of drag coefficient reductions for various boat-tail configurations. The vehicle chosen is an arbitrary streamlined front end with a width to height ratio of 64%. No tractor to trailer gap is modeled. Approximate model scale is 12% and test Reynolds Number is ∼850,000. Experimental data and numerical simulations are presented for the zero yaw angle condition. For boat-tail angles where the flow remains largely attached a relationship is observed between drag reduction and the minimum boat-tail area. An optimum boat-tail angle (in the range of 15 degrees) is identified for 0 degrees yaw from both experimental and numerical data. For boat-tail angles greater than optimum a distinct increase in drag is observed in the experimental data, which is associated with flow separation. Comparison of experimental and numerical results show reasonable agreement for attached flow cases, and indicate a similar optimal boat-tail angle.Copyright

Numerical Analysis of a Zero Energy Villa in the UAE

There is significant evidence that the world is warming up and the increasing temperatures will impact the built environment, particularly the energy requirement for airconditioning of the buildings. According to International Panel of Climate Change, during the end of 21st century, there would be steady increase in the global surface temperature [1]. The harsh and extreme climates in the UAE, puts forward various hurdles for different technologies to be used in order to reduce the energy consumption, and make the house more sustainable. In order to reduce the carbon footprint of buildings in the UAE, a villa is designed and modelled to become Zero Energy, located in Hatta, Dubai. In order to achieve the former objective, different insulation materials such as Polyisocyanurate, aerated and low density concrete, high efficient electrical equipment and air conditioning as well as low solar heat gain coefficient windows with a reflective coating were considered in this study. AutoCAD was initially used to sketch the plan of the villa and then further simulations were carried out on IES-VE (2015), to determine the electrical and cooling load of the house. Using the passive technologies, and keeping in mind the Thermal Comfort Index, per the ASHRAE standards, a reduction in cooling load of about 40% is observed when compared with a base case scenario. As the paper mainly focuses on drafting a villa which is off-grid, the energy demand of the house is provided by the PV system. Furthermore, a sensitivity analysis was conducted by varying the orientation and cooling profiles of the house on IES to draft a range of results. Changing the orientation of the house by 90° gave about a 2.3% reduction in the cooling load. When the results were compared with literature and base case, it proved that the values obtained were lower than the ones in similar case studies.

Effective U-Value of Wall Assemblies for an Eco-Friendly Paint Coating

The increased amount of carbon dioxide emissions in the atmosphere, and the rapid depletion of fossil fuels have urged the humans to develop technologies that lead in the direction of a sustainable future. The present study was carried out to investigate the effect of U-Values of buildings and villas in the Gulf Cooperation Council (GCC) region. The effective U-Value of two different types of roof assemblies of the GCC region was determined, and comparisons were also made between the U-Values for a standard and eco-friendly paint coating. Four different chambers were designed for this project, which had similar wall assemblies, but different roof specifications. Different parameters were collected and recorded, which showed a minimum of 5 % and a maximum of 11 % reduction in the electrical usage and U-Value for the rooftops that were coated with the eco-friendly paint. It was also observed that the effects of the eco-friendly paint were more prominent when an insulation layer was present in the wall envelope of the roof.

Fibre Bragg Grating use in Fluid Dynamic Studies

The application of fibre Bragg grating sensors for strain and force measurements in fluid dynamic experimental studies is presented. In the first example, a fibre Bragg grating is used as both a tether and a strain gauge for studies of neutrally buoyant spheres. The measured strains on the tether were found to agree well with the theory for the flow rates tested (0.14 to 0.33 m/s). In the second example a Bragg grating sensor has been used to monitor the forces acting on a cylinder as a function of flow rate and when the cylinder is translated in a stationary fluid. Excellent agreement was found between the vibration frequencies of the cylinder as measured by the Bragg grating and with a camera use to record the motion of the cylinder.