Characterization of counter-rotating streamwise vortices in flat rectangular channel with one-sided wavy wall

Particle Image Velocimetry (PIV) has been used to characterize the evolution of counter-rotating streamwise vortices in a rectangular channel with one sided wavy surface. The vortices were created by a uniform set of saw-tooth carved over the leading edge of a flat plate at the entrance of a flat rectangular channel with one-sided wavy wall. PIV measurements were taken over the spanwise and streamwise planes at different locations and at Reynolds number of 2500. Two other Reynolds numbers of 2885 and 3333 have also been considered for quantification purpose. Pairs of counter-rotating streamwise vortices have been shown experimentally to be centred along the spanwise direction at the saw-tooth valley where the vorticity ωz=0. It has also been found that the vorticity ωz of the pairs of counter-rotating vortices decreases along the streamwise direction, and increases with the Reynolds number. Moreover, different quantifications of such counter-rotating vortices have been discussed such as their size, boundary layer, velocity profile and vorticity. The current study shows that the mixing due to the wall shear stress of counter-rotating streamwise vortices as well as their averaged viscous dissipation rate of kinetic energy decrease over flat and adverse pressure gradient surfaces while increasing over favourable pressure gradient surfaces. Finally, it was also demonstrated that the main direction of stretching is orientated at around 45° with the main flow direction

Visualization of pre-set vortices in boundary layer flow over wavy surface in rectangular channel

Smoke-wire flow visualization is used to study the development of pre-set counter-rotating streamwise vortices in boundary layer flow over a wavy surface in a rectangular channel. The formation of the vortices is indicated by the vortical structures on the cross-sectional plane normal to the wavy surface. To obtain uniform spanwise vortex wavelength which will result in uniform vortex size, two types of spanwise disturbances were used: a series of perturbation wires placed prior and normal to the leading edge of the wavy surface, and a jagged pattern in the form of uniform triangles cut at the leading edge. These perturbation wires and jagged pattern induce low-velocity streaks that result in the formation of counter-rotating streamwise vortices that evolve downstream to form the mushroom-like structures on the cross-sectional plane of the flow. The evolution of the most amplified disturbances can be attributed to the formation of these mushroom-like structures. It is also shown that the size of the mushroom-like structures depends on the channel entrance geometry, Reynolds number, and the channel gap. Graphical Abstract: [Figure not available: see fulltext.

The effect of tax structure in economic growth

The main goal of this paper is to analyse the effect of the tax structure in the economic growth of Kosovo in the period 2007-2015. The study intends to evaluate the impact of specific types of taxes on economic growth. The methodology is based on comparative analysis of data using primary and secondary sources. Through the econometric model and linear regression analysis, the research hypotheses have been tested with STATA application/software to calculate the impact of tax structure in economic growth. The econometric model includes several independent variables (types of taxes), and the dependent variable GDP. Based on data obtained through the log-log model, the results show the impact of special taxes such as Pt, It, VAT, Wt, Ibt, Tdr.., Ct on GDP. The results show that most of the taxes have a positive impact on GDP growth; it is also shown that not all taxes have the same impact on economic growth. In the econometric analysis the coefficient of R2=0,999 reflects the high degree of determination with 99.9% forecasting accuracy.peer-reviewe

Effect of rounded edged dimple arrays on the boundary layer development

Journal of Visualization12117-2

Development of boundary-layer flow in the presence of forced wavelength Görtler vortices

10.1063/1.1789771Physics of Fluids16113983-3996PHFL

Similarity of a wall jet with a uniform external stream and tangential suction

46th AIAA Aerospace Sciences Meeting and Exhibit

Splitting and merging of Görtler vortices

10.1063/1.2151227Physics of Fluids17121-12PHFL

Secondary instability in forced wavelength Görtler vortices

10.1063/1.1941367Physics of Fluids1771-8PHFL

Development of most amplified wavelength Görtler vortices

10.1063/1.2160523Physics of Fluids181-PHFL

On the development of concave surface boundary layer flows

10.1063/1.3464849AIP Conference Proceedings122510-2