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The offset jet configuration is one where the jet is discharged at some distance from a solid surface. Although the geometric configuration may look simple, the flow may involve several complexities. In propulsion systems, the high-speed jet generated from the rear engine of an aircraft, flowing nearby the fuselage, can be treated as an offset jet. In this work, an experimental investigation of the interaction noise due to circular high-speed offset jets is performed in an anechoic environment at different nozzle pressure ratios and offset ratios (height of the jet centerline above the plate per nozzle width). A large horizontal plate placed over a height-adjustable stand is used as the offset plate. Acoustic characteristics such as overall sound pressure level and the directivity pattern of free and offset jets are compared for different nozzle pressure ratios. The effect of offset ratio on noise characteristics is also investigated. Flow visualization is also carried out to understand the shock structure and its noise generation mechanism. Acoustic characteristics reveal that noise levels are higher for an offset jet compared to a free jet. Sound pressure levels for offset ratio 0.5 are lower than those for other offset ratios. The noise levels are higher for offset ratio 1.0 due to the presence of feedback tone. Schlieren visualization studies also corroborate the above characteristics. [ABSTRACT FROM AUTHOR]

• The performance of vanes with different cooling structures were experimentally studied. • Jet impingement, BR increase and TR increase can all enhance the cooling performance. • Vane 2 with all impingement holes located upstream of the film hole inlet had the best cooling performance. • The offset jet resulted in a maximum enhancement of 8.75 % in integrated cooling effectiveness. • The integrated cooling effectiveness growth rate decreased as the BR increase. To investigate the performance of impingement/film combined cooling methods on the turbine vane pressure surface of leading cavity, typical cooling techniques and potential configurations were designed. The conjugate heat transfer experiments were carried out. Four different vanes were tested in the experiments, including Vane 0 (typical film cooling without jets), Vane 1 (typical impingement/film cooling with centerline normal jets), Vane 2 (impingement/film cooling with offset jets), and Vane 3 (impingement/film cooling with staggered offset jets). The effects of impingement hole position, BR (blowing ratio), and TR (temperature ratio of mainstream and coolant) were investigated. The experimental results show that the turbine vane cooling characteristics were determined by internal cooling, external cooling, vane heat conduction and coolant parameters jointly. Jet impingement, BR increase and TR increase can enhance the cooling performance. Compared with Vane 0, the overall-averaged ICE (integrated cooling effectiveness) of Vanes 1, 2, and 3 increased by 1.95 %–8.75 %. Due to the offset of the impingement hole, the jet impingement enhanced heat transfer region of Vane 2 was relatively independent of the gas film coverage region, the ICE of Vane 2 was more uniform and greater. With increasing of blowing ratio and temperature ratio, the ICE gradually increased, but the growth rate gradually decreased. Four alternative cooling structures for the pressure surface of leading cavity were tested at different working conditions and the experimental results can be used to support the design of the cooling structure for the turbine vanes. [ABSTRACT FROM AUTHOR]

Combined turbulent wall and offset jets with and without the presence of a parallel co-flow stream are investigated using the k-ω turbulence model. We focus on the effects of co-flow velocity on the locations of various characteristic points formed owing to the interaction of wall and offset jets in the dual jet flow. The inlet Reynolds number is taken as 15,000 and the offset ratio is varied from 5 to 11. At low offset ratios, the co-flow velocity effect remains almost negligible. With the progressive increase in co-flow velocity, the characteristic points are gradually relocated towards the further downstream direction with a transverse movement away from the bottom wall whose effect is weakened with the increase in co-flow velocity. Furthermore, regression analysis shows power law and linear correlations of the longitudinal and transverse coordinates of characteristic points with the co-flow velocity and the offset ratio. [ABSTRACT FROM AUTHOR]

The present numerical study aims to numerically investigate the dynamic and turbulent characteristics of a two-dimensional and turbulent offset jet. Three different parameters were investigated: The Reynolds numbers (Re) which was varied from 10000 to 30000, wall inclination angle (α) that was from −20° to +20° and finally the offset ratio (OR) which extends from 3.25–13. Ansys Fluent was numerical CFD solver used in this present investigation. The simultaneous effects of the OR, Re and α were investigated in details. The velocity and pressure contours showed that these three parameters do not contribute equally in the development of such a flow. Also, the turbulent characteristics, such as the turbulence intensities and energies depicted how each parameter influences, separately, the turbulent flow production. Furthermore, different of tripled parameters correlations were developed. These correlations may be of help to more understand certain offset jet flow features more accurately and to predict their exact values. [ABSTRACT FROM AUTHOR]

Inclined jet impingement is used for various industrial cooling applications. Its manufacturing and ease of applications is making it more popular day by day. The hot flat target surface is cooled using jet impingement. The jet is kept at an inclination of 15 -75° to hot target plate. The experiments are performed to study cooling effect with different configurations of inclined jets. Inclined jet with air as fluid having Reynolds number in the range of 2,000 ≤ Re ≤ 20,000 is examined for the circular cross section of jet. The target surface to jet perpendicular height (H) is taken as 0.5 ≤ H/D ≤ 6.8. The maximum cooled spots on the target surface are identified on the plate by analyzing maximum Nusselt numbers at different locations. The effect of H and (H/D) on maximum Nusselt number is presented. The investigation leads to equations for maximum Nusselt number for inclined circular non-confined air jet in terms of Reynolds number. Also analysis is carried out for ratio of average Nusselt number to maximum Nusselt number. [ABSTRACT FROM AUTHOR]

The flow characteristics of a submerged three-dimensional offset jet over transverse square ribs and gravel are experimentally investigated using an acoustic Doppler velocimeter. The pitch-to-height ratio of the ribs was varied to achieved-type, intermediate, andk-type roughness. The Reynolds number based on the nozzle height and jet exit bulk velocity was 53,000. The mean flow properties and turbulent statistics are compared to those obtained over a smooth surface. Both decay and wall-normal spread rates were independent of surface roughness with estimated values of 0.66 ± 0.03 and 0.138 ± 0.01, respectively, with these values influenced by the presence of lateral confinement of the flow. The distribution of the mean flow, within the inner shear layer, revealed a dependence on surface roughness after reattachment. A representation of the Reynolds normal stresses within the symmetry and lateral planes revealed the highly anisotropic nature of the turbulence field of offset jets. [ABSTRACT FROM PUBLISHER]

A three-dimensional offset jet flow over a surface mounted square rib was investigated using particle image velocimetry at Reynolds number of 7600. The square rib was mounted at three different locations downstream of the nozzle exit. Contour and profile plots in the symmetry plane were used to investigate the effect of the rib on the mean flow distribution and turbulence statistics. Changing the rib location enhanced the mixing and entrainment characteristics of the jet thereby leading to larger wall-normal spread rates. The quadrant analysis revealed a significant contribution of all events towards the Reynolds shear stress. The joint probability density function analysis showed that the structures within the outer shear layer of the jet differed from those of boundary layers. Results from the two-point correlation analysis indicated that the introduction of a surface mounted rib modified the flow structures within the developing region. However, there was no significant structural difference between the flow with mounted rib and the no rib case within the self-similar region. The proper orthogonal decomposition was used to examine how changes in rib location modified the dynamics of the energetic modes towards the turbulent kinetic energy and Reynolds shear stress within the developing and self-similar regions. [ABSTRACT FROM AUTHOR]

In this paper an offset, attached jet is investigated both experimentally and numerically, applying the tangential room air distribution system. The attachment distance of the injected air jet, which influences the ventilation characteristics in the room, is investigated as a function of the inlet Reynolds-number. Results showed that the attachment distance is independent from the inlet Reynolds- number in the range of Re0 = 2 ÷ 4 * 103 with fixed boundary conditions in a room. In the past decades several researchers have investigated offset jets. However, the tangential room air distribution as a type of comfort ventilation and lower Reynolds numbers have not been considered. Air velocity magnitude was measured in the injected air jet by a hot-wire anemometer. Three turbulence models were applied for the 3D numerical simulation: standard, RNG k-ε and SST k-ω models. In the present work the SST k-ω model seemed to be the most accurate turbulence model. The numerical results showed a high similarity with the measured data. [ABSTRACT FROM AUTHOR]

The present study considers a computational model to simulate conjugate heat transfer to a turbulent dual offset jet from a heated wall having a finite thickness and subjected to a constant wall temperature. To capture the effects of turbulence on the flow and heat transfer, the Reynolds Averaged Navier–Stokes equations (RANS) with the standard k − ε turbulence model have been employed. The convection equation in the flow regime is solved together with the conduction equation in the solid medium iteratively. For the purpose of the analysis, four parameters, namely, the Reynolds number (R e), the thermal conductivity ratio of the solid material and the fluid, the solid wall thickness, and the fluid Prandtl number (P r), are varied within suitable ranges. The flow field solution exhibits two recirculation zones; the first one is enclosed by the two jets and the other is formed underneath the lower jet. Conjugate heat transfer to the dual offset jet flow is analysed through the distribution of temperature, heat flux, and Nusselt number, at the interface between the fluid and solid regions. Results indicate that the non-dimensional temperature and heat flux profiles along the fluid–solid interface depend on all four parameters. In contrast, the distribution of the Nusselt number along the fluid–solid interface depends only on the Reynolds number and the Prandtl number. Increasing either of them leads to an overall increase in the interface Nusselt number. A correlation for the average Nusselt number along the interface is presented as a function of R e and P r. [ABSTRACT FROM AUTHOR]

• Peak in Nusselt number is associated with a change-of-sign of the skin-friction coefficient. • Turbulence production is largest in the recirculation region of the domain. • The recirculation region consists of four recirculating bubbles in a time-average sense. • Heat transfer from the wall is most effective in the recirculation region. • The peaks in wall-normal Reynolds shear stresses decrease with the streamwise direction. Planar wall-attaching offset jets can be found in a variety of engineering applications. In the present work, a planar turbulent offset wall-jet, at a Reynolds number of 7500 and an offset-ratio of 5, with heat transfer is numerically studied using large-eddy simulation (LES). First, a grid sensitivity study is performed and the quality of the mesh used is assessed using LES index of quality of resolution and an appropriate mesh is selected. Next, the solver is validated for mean streamwise velocity, streamwise Reynolds normal stress, and the evolution of coefficient of pressure on the wall, using reference experimental data from the literature. Thereafter, the unsteady flow features of the jet, maximum velocity decay and jet-spread, statistical features of flow and temperature, and turbulent kinetic energy (TKE) budgets and in-plane component of Reynolds shear stress are studied. The streamwise evolution of Nusselt number on the wall shows three distinct peaks and the location of these peaks correlates with a change-of-sign of the wall skin-friction coefficient. The domain can be categorized into three distinct regions namely, the recirculation, impingement and wall-jet regions. Distinct flow and thermal characteristics are observed depending on the region of interest. The peak magnitudes of Reynolds normal and shear stresses increase as one moves from the recirculation region to the impingement region and decreases thereafter attaining a lowest value in the wall-jet region. The heat transfer from the wall is observed to be most effective in the recirculation region. The production of TKE is dominant in all the three regions of the flow, whereas the Reynolds shear stress budgets indicate that the production and velocity–pressure-gradient terms are dominant and balance each other in all the three regions of the flow. [ABSTRACT FROM AUTHOR]

The present research is focused on computational analysis of conjugate heat transfer behavior of a turbulent offset jet flow over a moving flat plate in a quiescent environment. The plate of definite thickness and conductivity is subjected to isothermal condition at the plate bottom surface. The computation is carried out with a low-Reynolds number (LRN) turbulence model proposed by Yang and Shih which involves integration to wall (ITW) approach to capture the thin viscous sub-layer region within the boundary layer. The variation of offset ratio (ranging as 3, 7 and 11) and plate velocity (U p = 0 − 2) plays quite a major role in the distribution of interface temperature and Nusselt number. The conduction heat flow rate in solid depends upon the plate thickness ratio (S) which is varied as 0.5 − 1.5 and the conductivity ratio (K) ranging as 500 − 2000. The variation of average Nusselt number gives evidence of better cooling rate for smaller offset ratios and higher plate to jet velocity ratio. [ABSTRACT FROM AUTHOR]

The present paper deals with a turbulent dual jet consisting of a wall jet and an offset jet. The flow field has been numerically simulated using two-dimensional unsteady RANS equations. The Reynolds number based on the separation distance between the two jets ( s ) is R e = 10 , 000 . The width of the offset jet nozzle equals the separation distance between the two jets. To examine the influence of the bottom wall, the width of the wall jet nozzle ( h ) has been varied in a range 0.2 ≤ h / s ≤ 2 . According to the computational results, for h / s = 0.2 , the flow field remains to be always steady with two counter-rotating stable vortices in between the two jets. On the contrary, within the range of 0.3 ≤ h / s ≤ 1 , the near flow field demonstrates a periodic vortex shedding phenomenon similar to what would be observed in the near wake region for flow over a two-dimensional bluff body. Within this flow regime, the Strouhal number based on the vortex shedding frequency gradually decreases with the progressive increase in h / s . However, for h / s > 1 , although the periodic vortex shedding phenomenon is still evident in the flow field, the Strouhal number becomes insensitive to the bottom wall similar to the flow behaviour for a flow over an unconfined cylinder. [ABSTRACT FROM AUTHOR]

This paper presents a study of the conjugate heat transfer, involving conduction through a solid slab and turbulent convection in fluid, for a combined turbulent wall jet and offset jet flow using unsteady Reynolds averaged Navier-Stokes (URANS) equations. The conduction equation for the solid slab and convection equation for the fluid region are solved simultaneously satisfying the equality of temperature and heat flux at the solid-fluid interface. The fluid flow is complex because of the existence of periodically unsteady interaction between the two jets for the chosen ratio of jets separation distance to the jet width (i.e., dlw = l). The heat transfer characteristics at the solid-fluid interface have been investigated by varying various important parameters within a feasible range: Reynolds number (Re = 10,000--20,000), Prandtl number (Pr = 1-4), solid-to-fluid thermal conductivity ratio (kslkf= 1000-4000), and nondimensional solid slab thickness (s/w = 1-10). The bottom swface of the solid slab has been maintained at a constant temperature. The mean conjugate heat transfer characteristics indicate that the mean local Nusselt number along the interface is a function of flow (Re) as well as fluid (Pr) properties but is independent of solid properties (ks and s). However, the mean inteiface temperature and mean local heat flux along the inteiface always depend on all the aforementioned properties. [ABSTRACT FROM AUTHOR]

Three-dimensional turbulent offset jets were investigated using a particle image velocimetry technique. Detailed measurements were performed for offset height ratios of 0, 2 and 4. The presence of backflow influenced the distribution of the mean velocity and Reynolds stresses. A two-point correlation analysis was used to investigate the spatial distribution of large-scale structures within the inner shear layer of the flow domain. The results revealed that large-scale structures dominate the inner layer of the self-similarity region. Proper orthogonal decomposition was performed on the fluctuating velocity field within the symmetry and lateral planes using the snapshot approach. Results from the reconstructed field provided insight into the contributions of the most energetic structures to the turbulence statistics. The energetic structures contributed more to the Reynolds shear stress and streamwise turbulence intensity, while contributing less to the wall-normal turbulence intensity. [ABSTRACT FROM PUBLISHER]

The present study investigates the flow characteristics within the recirculation region of three-dimensional offset jets using a particle image velocimetry technique. Measurements were performed for four nozzle offset height ratios of 0, 2, 4 and 8. The discharged jet entrained the ambient fluid as depicted by streamlines superimposed on the mean velocity contours. Analysis of the flow field showed that the maximum streamwise mean velocity decay rate increased with increasing offset height ratio. Wall-normal spread rates of 0.066 and 0.016 were obtained for jets with offset height ratios of 0 and 2, respectively, and lateral spread rates of 0.116, 0.114 and 0.096 for jets with offset height ratios of 0, 2 and 4, respectively. The reattachment lengths of the jets increased with increasing offset height ratio. Profiles of the mean velocities, Reynolds stresses and some of the budget terms (specifically, production, diffusion and convective terms) of the turbulent kinetic energy have been investigated. It was observed that increasing the offset height ratio influenced the distribution of these quantities within the recirculation region. A two-point velocity correlation analysis was performed to analyse the flow structures within the recirculation region. The two-point correlation revealed some large-scale structures which were observed to increase in size as the offset height ratio increased. The two-point correlation analysis also revealed that the estimated integral length scales within the recirculation region of the flow increased with increasing offset height ratio. [ABSTRACT FROM AUTHOR]

The present study examines the configuration of an offset jet issuing into either a quiescent medium or a moving stream (co-flowing). The mean velocity and turbulence characteristics of the turbulent offset jet have been investigated using a particle image velocimetry technique at three velocity ratios and for two offset ratios. A numerical simulation of a threedimensional offset jet has also been carried out by comparing the corresponding results with previous experimental data and our measurements. The numerical investigation was performed by means of the finite volume method together with a second-order turbulent closure model - the Reynolds stress model (RSM) - to examine the behavior of the flow for different velocity ratio and offset ratios. Results give a satisfactory agreement between the experimental data and the calculations. Data from the early flow region clearly show a significant influence of the velocity ratio and the offset ratio on the mean flow and turbulence characteristics. [ABSTRACT FROM AUTHOR]

The effects of separation distance between two jets in the near field region of turbulent dual jet flow consisting of a wall jet flow and an offset jet flow have been investigated using two-dimensional unsteady RANS equations. The unsteady fluid mechanics of two interacting jets have been illustrated by means of time series analysis of the instantaneous flow field. For a comprehensive understanding of the fluid mechanics, computation has been carried out at a large number of values of the ratio of separation distance ( d ) and jet width ( w ) for finely resolving the relevant range of d/w . Results show that when d/w lies in the range 0.7 ≤ d / w ≤ 2.1 , the near field of the flow domain is characterized by a periodic large scale von Kármán-like vortex shedding phenomenon similar to what would be expected in the wake of a bluff body. On the contrary, for d / w ≤ 0.6 and d / w ≥ 2.2 , no periodic vortex shedding is detected; rather, a pair of steady counter rotating stable vortices are formed in between the two jets close to the nozzle plate. Fast Fourier transform of the velocity signals provides vortex shedding frequency corresponding to the Strouhal number that decreases with the increase in separation distance between the two jets. [ABSTRACT FROM AUTHOR]

Abstract: A comparative study of flow field and turbulence characteristics of a turbulent offset jet has been done. The computational results obtained from low-Reynolds number k–ϵ models proposed by Launder and Sharma, and Yang and Shih are compared with that of the standard k–ϵ model. The existence of Moffatt vortices (secondary recirculation region) have been identified near the corner of the wall for low-Reynolds number modeling. A velocity similarity profile has been observed as expected due to the resemblance of an offset jet with that of the wall jet flow in the wall jet region. The linear law of the wall (u + = y +) has been found to be valid up to y + ≈3.0 in the wall jet region which agrees with the experimental results. The integral constant of momentum flux is higher for lower offset ratio due to a smaller recirculation region. The distribution of pressure field, Reynolds shear stress, budget of turbulent kinetic energy in the recirculation region and the jet characteristic parameters such as variation of the jet half-width (Y 0.5) along the streamwise direction and decay of the maximum streamwise velocity are discussed in detail. [Copyright &y& Elsevier]

Abstract: The mixed convection flow and heat transfer characteristics in a two-dimensional plane, laminar offset jet issuing parallel to an isothermal flat plate have been investigated numerically. The unsteady form of the vorticity transport equation has been solved to obtain the steady-state solution. The isothermal heated plate is 30 times the jet width and the offset ratio is 1. The behavior of the jet in the range of Reynolds number and Grashof number is described in details. The medium considered is air (Pr =0.71). It is found that the reattachment length is strongly dependent on both Re and Gr for the range considered. Simulations are made to show the effect of entrainment on the recirculation eddy. The variation of the local Nusselt number is presented for various Re and Gr. An empirical correlation of average Nusselt number as a function of Richardson number and Re has been given. [Copyright &y& Elsevier]

Abstract: Heat transfer from an isothermal plate by a two-dimensional laminar incompressible offset jet is simulated numerically. The heat transfer characteristics of the jet with respect to offset ratio (OR), Reynolds number (Re) and Prandtl number (Pr) are reported in details. At low Pr, conduction mode of heat transfer is dominant in the region. The isotherm is studied inside the recirculation region as well as in the reattachment location. The thermal boundary layer thickness is reduced when Pr is increased. Nusselt number is calculated for different OR and wide range of Re and , 1 and 100. The variation of the average Nusselt number with different parameters is also reported in details. [Copyright &y& Elsevier]

In this paper the offset jet entering a domain with a movable bed is simulated by the computer program FLUENT. To achieve this aim, sediment transport is numerically simulated using multiphase systems and the empirical coefficients are studied theoretically. The numerical results are verified by comparing the simulated total load with that obtained using existing formulae and concentration profiles from available measured data. In the final step, the offset jet scouring pattern is modeled qualitatively. [ABSTRACT FROM AUTHOR]

Offset jet is a commonly used flow in different industrial applications, such as in cooling electronic devices or heat exchange systems. Determining the exact behaviour of the thermal characteristics of such flow, as a function of several independent parameters, is quite interesting and useful. The aim of the current study of an inclined heated and turbulent offset jet is to investigate numerically the dynamic and thermal characteristics of the flow. To figure out which parameter is the most significant for the heat transfer process, The effects of the Reynolds number (Re), the offset ratio (OR) and the inclination angle(α) were discussed in details. Note that the OR is varied in two domains: from 20,000 to 40,000, from 5 to 15 and the inclination angle is varied from −20° to +20°. The simulations are carried out using the CFD solver Ansys Fluent. The SST k-ω turbulence model was selected among four different turbulence models and using the velocity-pressure coupling. Velocity and pressure and streamlines, contours are provided to examine the dynamic behaviour of the flow. Furthermore, local Nusselt evolution is presented for different parameter combinations (Re , OR and α) to outline their simultaneous effects on the convective transfer phenomenon. Finally, based on the gathering data, triple-parameter correlations were developed to govern the maximum Nu value and the average Nusselt estimations throughout the different flow's zones. These correlations will broad the current knowledge in different engineering applications to enhance the heat transfer in different heat exchange systems such as electronics cooling systems. [ABSTRACT FROM AUTHOR]

The present study investigates numerically the effect of wall undulation on the thermo-hydraulic transport characteristics of turbulent jet. In order to explore the influence of position of the nozzle exit from the wall, both wall jet and offset jet are considered. The theoretical model is numerically solved using shear stress transport (SST) model to predict the effects of height of undulation of the wall and the offset jet ratio on the re-attachment length, the velocity profile at different downstream locations, the coefficient of friction and the Nusselt number. The results indicate that the undulation of wall has a strong influence in altering the friction coefficient, Nusselt number and re-attachment length for offset jet. It further reveals that there is an intricate interplay between undulation height and offset ratio in dictating the flow and heat transfer characteristics. • Effect of wall undulation on thermo-hydraulic transport characteristics of turbulent jet. • Strong influence of undulation of wall on the transport characteristics. • Intricate interplay between undulation height and offset ratio for offset jet. [ABSTRACT FROM AUTHOR]

• The behavior of a 3D turbulent offset jet injected with different densities was experimentally investigated. • The flow visualization and mean velocity measurements were conducted using a Laser Doppler Velocimetry (LDV) technique. • The effects of the density ratio and the offset height ratio on the flow structure were examined. • The reattachment length of offset jets with various jet densities was estimated and validated numerically. This paper presents the results of measurements and numerical predictions of 3D turbulent offset jet flows. Mean velocity and turbulence characteristics of a rectangular offset jet with different offset heights and within variable densities are experimentally and numerically investigated in detail. Four jet gas exit densities, ρ j = 1.2, 1.25, 1.3 and 1.4 Kg/m3, and four offset ratios, h/ w = 8, 16, 25 and 33, are studied. The considered variation of the jet density is revealed at different Reynolds numbers and the velocity measurements are carried out using a Laser Doppler Velocimetry (LDV) technique. The handled configuration is numerically simulated by solving the Navier-Stokes equations with the finite volume method having a non-uniform grid system. Two different closure models are tested: the standard k–ε model and the Reynolds Stress Model (RSM). Results clearly revealed significant effects of the jet density and the offset height on the flow development in the early region. It is noted that the centerline velocity decay increases as the jet density and the offset height increase. It is also observed that the reattachment length of the jet decreases with the increase of the jet density. However, the reattachment length is found to increase with the increase of the offset height. [ABSTRACT FROM AUTHOR]