Effect of gap flow on the shallow wake of a sharp-edged bluff body – turbulence parameters

This experimental study was carried out to investigate the turbulent wake generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. The objective of this study is to understand the effect of the gap flow on the turbulent wake by studying two different gap heights between the channel bed and the bottom edge of the bluff body. These two cases were compared to the no-gap case which is considered as a reference case. The maximum flow velocity was 0.45 m/s and the Reynolds number based on the water depthwas 45,000. Extensivemeasurements of the flow field in the vertical mid-plane and in the horizontal near-bed, mid-depth, and near-surface planes weremade using particle-image velocimetry (PIV). This paper is the second part of an extensive study to characterise the gap-flow effects and is primarily focused on the mean and instantaneous turbulence quantities as well as coherent structures. The results revealed that the gap flow increased the transfer of the turbulent kinetic energy (TKE) from the streamwise to the vertical component along the vertical mid-plane. In addition, there is a corresponding increase and spread of the transverse component in the transverse direction as the flow evolves in the downstream direction. The momentum exchange by the Reynolds stress is significantly weak in the vertical mid-plane particularly in the lower half of the water depth, but the gap flow enhanced the momentum exchange in the upper half of the water depth by up to 1% of the freestream velocity squared. Furthermore, the intensity and bursting direction of the turbulence fluctuations in the far field are also affected by the gap flow when it is large. Furthermore, the proper orthogonal decomposition results revealed that the flow contains a large number of structures, and their interactions are responsible for deforming and/or tearing apart the structures, and transferring fluid throughout the velocity field

Effect of gap flow on the shallow wake of a sharp-edged bluff body –mean velocity fields

This experimental study was carried out to investigate the turbulent shallow wake generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. The objective of this study is to understand the effect of the gap flow on the wake by studying two different gap heights between the channel bed and the bottom edge of the bluff body. These two cases will be compared to the no-gap case which is considered as a reference case. Themaximumflowvelocity was 0.45m/s and the Reynolds number based on the water depthwas 45,000. Extensivemeasurements of the flowfield in the verticalmid-plane and in the horizontal near-bed, mid-depth, and near-surface planes weremade using particle image velocimetry. This paper is part of an extensive study to characterise the gap-flow effects and is primarily concerned with the mean velocity fields, while a companion paper discusses the turbulence characteristics. The size of the wake identified in the horizontal planes is found to vary in the three planes, where the gap flow enhances the entrainment in the near-wake region in the near-bed velocity field. The results also revealed that, if the gap flow is weak, it is engulfed by the recirculation zone formed just behind the bluff body whose axis is perpendicular to the vertical mid-plane. On the other hand, if the gap flow is relatively strong, it penetrates in the downstream direction and only a portion of it is diverted upward to feed the recirculation zone

E-Learning approach in Teacher Education

There has been an increasing interest in e-learning in teacher training at universities during the last ten years. With the developing technology, educational methods have differed as well as many other processes. Firstly, a definition on e-learning as a new approach should be given. E-learning could shortly be defined as a web-based educational system on platform with Internet, Intranet or computer access. In this model, the lessons planned were simulations and software’s for students on polymers and metals. Nine experiments were designed on the topic. Students were interviewed and administered laboratory attitude scales at the end of the experiments.  The study concluded that the experiments in the new model were appropriate to teacher training programs and could successfully be administered to large groups

Inviscid instability of streamwise corner flow

Linear stability of the incompressible flow along a stream wise corner is studied by solving the two-dimensional eigenvalue problem governed by partial differential equations. It is found that this fully three-dimensional flow is subject to inviscid instability due to the inflectional nature of the stream wise velocity profile. The higher growth rates for the inviscid instability mode, which is symmetric about the corner bisector, as compared to the viscous Tollmien-Schlichting instability operative away from the corner is consistent with the experimental findings that the corner flow transitions to turbulence earlier than the two-dimensional Blasius flow away from the corner

Particle Image Velocimetry (PIV) Investigation of Local Scour Around Emergent and Submerged Circular Cylinders

Analysis of the velocity field surrounding a circular cylinder under equilibrium of local scour has been restricted due to practical limitations of commonly used measurement techniques. This investigation summarizes select cases in the literature which have attempted to circumvent such limitations and presents flow field measurements using Particle Image Velocimetry (PIV). Scour tests were conducted in a horizontal flume fitted with a sediment recess containing erodible bed material. Tests were conducted with both emergent and submerged circular cylinders for a period of 24 hours, after which equilibrium was achieved and planar PIV measurements were obtained in the streamwise-vertical symmetry plane. Analysis of bed profiles and the distribution of the mean velocity indicated that the scour depth upstream of the cylinder was slightly (2 percent) higher for the emergent case, and separation of flow over the top of the submerged cylinder affected the formation of the dune in the wake of the cylinder

Cooling enhancement for engine parts using jet impingement

A computational study has been performed to evaluate the use of jet impingement for cooling applications in the automotive industry. The current study uses an entire internal combustion engine cylinder with its components as a computational domain. An unsteady numerical solution for the Navier-Stokes equations was carried out using Improved Delayed Detached Eddy Simulation (IDDES). The volume of fluid approach is proposed to track and locate the liquid jet surface that is in contact with the air. The conjugate heat transfer approach is used to link the heat transfer solution between the fluid and the solid. The boundary conditions that are employed in the study are provided from lab experiments and one-dimensional simulations. The cooling jet in this study targets the hottest region in the piston, i.e., the region underneath the exhaust valve. Three nozzle sizes with flows at different Reynolds numbers are chosen to examine the thermal characteristics of the cooling jet. The computational study reveals that for a specific Reynolds number, the smaller diameter nozzle provides the highest heat transfer coefficient around the impingement point. The maximum relative velocity location at the impingement point slightly leads the location of the maximum Nusselt number. The maximum temperature in the piston decreases by 7% to 11% as the nozzle diameter changes from 1.0 to 3.0 mm for a jet Reynolds number of 4,500. If a correct selection is made for the nozzle size, the cooling jet can be efficiently used to reduce the temperature and alleviate the thermal stresses in the piston in the region underneath the exhaust valve where the maximum temperature occurs

Wake simulations in shallow flows

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Three-dimensional numerical modeling using Detached Eddy Simulation (DES) has been carried out to study the characteristics of shallow wake flow. The features of shallow wake flows are highly dependent on the bed characteristics, the free surface and the non-uniform approaching flow velocity profile. An approaching flow with fully developed boundary layer was employed to model the effect of the shallow flow. The shallow wake is generated by introducing a disturbance in the form of a bluff body placed in an open channel. A sharp- edged bluff body is used to reduce the flow sensitivity to Reynolds number and maintain a constant position for boundary layer separation. The flow field structure in the wake i.e., the mean and turbulence characteristics, are examined and compared at different downstream locations to evaluate the effect of vertical variability from the bed. Available experimental data have been used to validate the computational results.dc201