Computational study of a turbulent wall jet flow on an oblique surface

Abstract

Purpose – The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and to investigate the effect of variation of the angle of inclination of the wall on the flow structure of the wall jet. Design/methodology/approach – The high Reynolds number two-equation κ− model with standard wall function is used as the turbulence model. The Reynolds number considered for the present study is 10,000. The Reynolds averaged Navier-Stokes (RANS) equations are used for predicting the turbulent flow. A staggered differencing technique employing both contravariant and Cartesian components of velocity has been applied. Results for distribution of wall static pressure and skin friction, decay of maximum streamwise velocity, streamwise variation of integral momentum and energy flux have been compared for the cases of α=0°, 5°, and 10°. Findings – Flow field has been represented in terms of streamwise and lateral velocity contours, static pressure contour, vorticity contour and streamwise velocity and static pressure profiles at different locations along the oblique offset plate. Distribution of Reynolds stresses in terms of spanwise, lateral and turbulent shear stresses, and turbulent kinetic energy and its dissipation rate have been presented to describe the turbulent characteristics. Similarity of streamwise velocity and the velocity parallel to the oblique wall has been observed in the developed region of the wall jet flow. A decaying trend is observed in the variation of total integral momentum flux in the developed region of the wall jet which becomes more evident with increase in oblique angle. Developed flow region has indicated trend of similarity in profiles of streamwise velocity as well as velocity component parallel to the oblique wall. A depression in wall static pressure has been observed near the nozzle exit when the wall is inclined and the depression increases with increase in inclination. Effect of variation of oblique angles on skin friction coefficient has indicated that it decreases with increase in oblique angle. Growth of the outer and inner shear layers and spread of the jet shows linear variation with distance along the oblique wall. Decay of maximum streamwise velocity is found to be unaffected by variation in oblique angle except in the far downstream region. The streamwise variation of spanwise integral energy shows increase in oblique angle and decreases the magnitude of energy flux through the domain. In the developed flow region, streamwise variation of centreline turbulent intensities shows increased values with increase in oblique angle, while turbulence intensities along the jet centreline in the region X<12 remain unaffected by change in oblique angles. Normalized turbulent kinetic energy distribution highlights the difference in turbulence characteristics between the wall jet and reattached offset jet flow. Near wall velocity distribution shows that the inner region of boundary layer of the developed oblique wall jet follows a logarithmic profile, but it shows some difference from the standard logarithmic curve of turbulent boundary layers which can be attributed to an increase in skin friction coefficient and a decrease in thickness of the wall attached layer. Originality/value – The study presents an in-depth investigation of the interaction between the jet and the inclined wall. It is shown that due to the Coanda effect, the jet follows the nearby wall. The findings will be useful in the study of combined flow of wall jet and offset jet and dual offset jet on oblique surfaces leading to a better design of some mechanical jet flow devices.

Enhancement of heat transfer using turbulent wall jet

“…The variation of pressure on the wavy wall is shown in Figure 4(a) for various amplitudes. For the comparison purpose, the pressure variation for a plane wall surface of Pramanik and Das 2 is also considered here. Pramanik and Das 2 noticed that the mean static pressure remains nearly constant along the plane wall.…”

“…The turbulent wall jet plays a significant role in both engineering and industrial applications. The turbulent wall jet is encountered in many practical engineering applications like cooling of a gas turbine blade, boiler combustion chamber, an automobile demister, air conditioning flow, space heating in the building, defrosters in automobile, electronics cooling, cooling of nanoelectromechanical systems, injection of steam in the combustion chamber [1][2][3][4][5][6] and so forth. A jet is known as the wall jet when the flow from the nozzle is discharged tangentially to a surface.…”

“…The associated challenges attracted many researchers. 2,7,8 Numerical study on inner and outer layers was carried out by using interactive eddy viscosity expression. 7 Recently, the effect of coflow stream on turbulence characteristics of a wall jet by using the low Reynolds number k-ɛ models of the first order was studied 9 and found that the decay of wall jet flow becomes faster when the directed coflow stream was present.…”

“…The orientation of a plate and surface roughness are also important parameters which drew the attention of several investigators. 2,8,11,12 The effect of friction coefficient and velocity profile on the flow characteristics was investigated using particle image velocimetry (PIV) technique. 11 For this experimental work, Re = 13,400 and roughness k = 0.44 mm were considered.…”

“…The skin friction coefficient and decay in maximum velocity for the rough surface showed a larger value as compared to the smooth wall surface. The turbulent characteristics of a wall jet flowing tangentially over an inclined plate was numerically studied 2,8 using standard k-ɛ turbulence model. A linear variation has been observed for growth in inner and outer shear layers.…”