Papers by Keyword: Boundary Layer

Abstract: Aim of the paper is to study the Magnetohydrodynamic boundary layer flow over a cone under the effect of joule heating and viscous dissipation. The surface of the cone is cooled and heated by the flowing fluid having constant temperature along with variable heat transfer coefficient.The surface of the cone is subjected under the convective heat flux. The governing equation for MHD boundary layer flow are non-linear partial differential equations, are transformed into ordinary differential equations using similarity techniques. The reduced ordinary coupled equations are solved with Runge-Kutta’s fourth order method followed by shooting techniques. The effects on flow and heat convection of various physical parameters pertinent to the modeled problem are computed and analyzed and shown through graphs. Keywords: Mixed convection, cone, Boundary layer, Joule Heating, Convective boundary condition.

Abstract: This paper investigates the effect of the laser cutting parameters on the heat-affected zone, and on the boundary layer of stainless steel processing. A new analytical resolution based on the boundary layer theory is used to deduce the interaction effects of the cutting parameters on the above zones. The results revealed that, the laminar nitrogen assist gas has a negligible effect on the HAZ depth but it has a remarkable effect on the molten boundary layer. It is also noticed that the pressure gradient remains very small compared to the interface shearing and the conductive heat losses from the cutting zone towards the substrate is dominant compared to the convective heat losses towards the gas.

Abstract: Aerodynamics is a relatively young scientific discipline, which started developing in the 50´s of last century. There are known several methods for calculating and measuring of the aerodynamic variables – in-situ measurements, wind tunnel measurements, CFD simulations and calculations according to national standards. Each method has its advantages and disadvantages. Nowadays a large focus is on experimental verifying the findings achieved with calculations help and CFD simulations. One of the verification possibilities are measurements in wind tunnels. The submitted paper deals with construction and using of the wind tunnel by the Slovak University of Technology in Bratislava. This device was put into operation after experimental verification in 2012, so this wind tunnel is one of the newest of its kind in Europe. The concept of the construction of individual structural elements and the wind tunnel parts has been designed in collaboration with the Aeronautical Research and Test Institute (Czech Republic) and was based on previous made analysis of aerodynamic tunnels. Its structure was designed and realized by Konštrukta Industry (Slovak Republic). We could it characterized as atmospheric boundary layer wind tunnel with open test section. It is unique with two test sections – front and back measuring space, where the front measuring space is used for uniform flow and the back measuring space is used for turbulent flow. That is why it is not only usable in the civil engineering sector (buildings, bridges, chimneys etc.), but also in city urbanism (pedestrian wind comfort and wind safety, dispersion of air pollutants), aircraft and automotive industries.

Abstract: The problem of fluid flow on air-jet weaving machine (i.e. mechanical engineering and chemical engineering) is deliberated upon in this report using the case of non-Newtonian Carreau fluid flow. In this report, the boundary layer flow of the fluid over an upper horizontal surface of a paraboloid of revolution is presented. The dimensional governing equations were non-dimensionalized, parameterized, solved numerically and discussed. Maximum horizontal velocity is ascertained at smaller values of thickness parameter, a larger value of buoyancy related parameter and the flow is characterized as shear-thickening. Local skin friction coefficient is an increasing and a decreasing property of Deborah number for Shear thinning and Shear-thickening cases of the flow respectively. The velocity of the flow parallel to the surface (uhspr) is a decreasing property of thickness parameter and increasing function of velocity index parameter.

Abstract: In this article, the problem of a non-Newtonian fluid (micropolar) flow over a horizontal melting surface in the presence of internal heat source and dual stretching (i.e. at the wall and at the free stream) is presented. Since the magnetic-Reynold of the flow is substantial, the influence of induced magnetic field is properly accounted in the governing equation. The viscosity and thermal conductivity of the micropolar fluid are considered to vary linearly with temperature. Classical models of these thermophysical properties were modified to suit the case of melting heat transfer. A similarity transformation is applied to reduce the governing partial differential equation to coupled ordinary differential equation corresponding to dimensionless momentum, angular momentum, energy and induced magnetic field equation. These equations along with the boundary conditions are solved numerically using shooting method along with Runge-Kutta-Gill method together with quadratic interpolation. The results of the present study indicate that due to the formation of boundary layer on melting surface (region of low heat energy) in the presence of induced magnetic field, space and temperature dependent internal heat generation enhances the heat transfer rate.

Abstract: This paper is concerned with the accurate prediction of parasitic drag due to excrescences introduced by structural repairs to aircraft wings and fuselage. Numerical computations are carried out to quantify the effect of isolated surface excrescences in a turbulent boundary layer on a flat plate. Both step excrescence in 2-D domain and wall-mounted hexahedron in 3-D domain are considered in the investigation. Various approaches for calculating drag coefficient increments for wing repair plates are presented. Menter's Shear Stress Transport (SST k-ω) turbulence model is employed here for its accurate prediction of aeronautics flows at typical repair locations with strong adverse pressure gradients and separation. Solutions are obtained via a high-order numerical scheme and an implicit time-marching approach on a multi-block structured mesh. A grid resolution study was carried out to confirm the accuracy of the computations. From the results curves are drawn showing the variation of parasitic drag components for a range of controlled speed (Mach 0.1 to 0.8), local Reynolds number (10⁴ to 10⁷) and the height of excrescence (y⁺=10² to 10⁴).

Abstract: This paper presents a numerical study on the flow dynamics and heat transfer behaviour of unsteady conjugate natural convection boundary layers (CNCBLs) in a partitioned, air filled square cavity. An unsteady two-dimensional multigrid-assisted solver is developed in the C#.NET programming language on stretched Cartesian meshes. The finite volume method is used to discretise the governing equations. To solve the coupled pressure and velocity, the SIMPLE algorithm is used, and to increase simulation accuracy the Adam-Bashforth, QUICK and central difference schemes are employed for time, convection, and diffusion terms respectively. The Poisson pressure equation is solved through the use of the multigrid method. The developed code is used to model CNCBLs which typically require a large amount of simulation time. The numerical results provide detailed descriptions of unsteady CNCBLs and associated heat transfer behaviour over a wide range of Ra, such as the thermal and viscous boundary layer thicknesses, temperature and velocity distributions, and maximum velocities within the CNCBLs.

Abstract: At the small town of Silsoe, UK , under the leadership of engineer Richards the model was made up with edge of the cube 6 m, used for research of wind on the model. Cube named Silsoe took over many laboratories in the world and diminished cube was tested in the wind tunnel. The aim of our study was to compare recently built the wind tunnel Faculty of Civil Engineering in Bratislava with other sites in the world. Suitable for this purpose served just cube model Silsoe of the edge of 200 mm, which was tested in the wind tunnel of Faculty of Civil Engineering and subsequently also in the workplace at VZLU Prague. The model coefficients were measured the pressure on the cladding of cube and compared with the other measurements. The test results are presented in this paper.

Abstract: This paper will present the development of a simple subsonic boundary layer method suitable to be used coupled with panel methods in order to estimate the aerodynamic characteristics, including viscous drag and maximum lift coefficient, of 3D wings. The proposed method does not require viscous-inviscid iterations and is based on classical integral bi-dimensional boundary layer theory using Thwaites and Head ́s models with bi-dimensional empirical corrections applied to each wing strip being therefor robust and efficient to be used in the early conceptual stage of aircraft design. Presented results are compared to the Modified CS Method in an IBL scheme and experimental data and are shown to provide good results.

Abstract: A “laminar + transition criteria” model utilizing Re_θ/M_e and Re_CF criteria in conjunction with an intermittency function Γ is developed in this paper. With pretreated computational grid and total enthalpy h₀=(h_0,∞)_max criteria the boundary layer edge and crossflow velocity can be obtained by using parallel methodology. Validation is accomplished via HIFiRE-5 and a blunt cone with small angle of attack. Results show that computed Re_θ/M_e and Re_CF distributions are similar to the N-factor for streamwise instability and crossflow instability from linear PSE methods. The shape and trend of transition regions predicted by the “laminar + transition criteria” model in HIFiRE-5 and blunt cone are in good agreement with the experiment and DNS. However, for the transition induced by inflection point on streamwise velocity profiles, using criteria related to boundary layer thickness is inappropriate and can predict transition onset prematurely.