Jet Boundary Layer Research Articles

Numerical investigation on flow field characteristics of dual synthetic cold/hot jets using POD and DMD methods

In order to improve the control ability of synthetic jets in compressible boundary layer, a novel control method based on dual synthetic cold/hot jets coupled control of velocity profile and temperature profile was proposed. As fundamental investigations on the effects of synthetic jet temperature on the jet behavior and flow field characteristics were essentially necessary, preliminary numerical simulations were conducted to study the influence of temperature (200 K and 400 K) on the flow field characteristics of synthetic jets using Large Eddy Simulations (LES) model. Time-averaged flow fields showed that different temperatures led to variable behavior of two strands of jets. For dual synthetic cold jets, a potential-core arose apparently with its height ranging from 0.01 to 0.03 m, while for dual synthetic hot jets, two strands of jets emerged downstream. The modal decomposition of instantaneous flow fields had been done using both Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD). Various modes showed different characteristics of the flow fields. As the POD method focuses on the energy of flow while the DMD method focuses on the frequency, the first two modes had many similarities, but the third and fourth modes demonstrated completely different vortex structures. The current researches play a role of preliminary investigations for further and comprehensive exploration of novel flow control measures in global velocity field.

Experimental Investigation of the Self-Ignition and Jet Flame of Hydrogen Jets Released under Different Conditions

Hydrogen is a promising clean energy source and an important chemical raw material. To use hydrogen energy more safely, a high-pressure hydrogen-release platform for hydrogen self-ignition and for generating hydrogen jet flames under different experimental conditions was investigated in this study. The associated experimental analysis was based on the theory of high-pressure hydrogen tube diffusion. We found that the higher the initial release pressure, the greater the intensity of the leading shock. When the initial release pressure was high and the leading shock intensity was strong, hydrogen was more likely to ignite spontaneously inside the tube. The higher the initial release pressure, the faster the average propagation speed of the shock in the same pipe length. The time during which a stable leading shock was formed inside the tube may be related to the initial release pressure. It was found that flame combustion intensified after the passage of air through a Mach disk, and a stable flame was formed more easily at the jet boundary layer away from the orifice axis. The maximum speed of the flame tip and the flame decay speed were very high. Moreover, the flame length and the diameter of the ball flame first increased and then decreased.

An Analytical Description of the Expansion of Plane Wall Jets

The effectiveness of forming microclimate of buildings and structures depends on the decisions of air exchange organization. One of the influencing factors of the efficiency of air exchange organization is the development of ventilation flow jets. In this case, the laying of jet streams on surfaces of the enclosing structures (wall jets) is widely used. In this work, the laws of the development of plane wall jets on the basis of geometric and kinematic analysis of large-scale vortex structure are obtained. For this purpose, a turbulent macrostructure scheme was constructed. The macrostructure is represented in the form of a sheet of tangent large-scale vortices (puffs) within the jet boundary layer. It is assumed that in the outer part between the puffs there is only the injection of the environmental liquid or gas to the jet in the direction perpendicular to the direction of its movement. In this case, when the puff moves, the jet should use the entire volume that the puff occupies on its path. Implementation of such model is most effective in computer aided design (CAD) systems, which allows automatic precise determination of the areas of complex figures. In this work, free version of DraftSight has been used To get the four exact signs of the tangent of the angle of expansion of the jet, there are only six iterations. The obtained results coincide with the known experimental data of G. Abramovych, which confirms the adequacy of the results obtained. Similar calculations have also been made for the refined hypothesis of I. Shepelev, which allows removing the wall boundary layer from consideration. Clarification of the hypothesis is that the jet boundary layer should be stretched to the wall. The difference in results is within 1 %, which allows to recommend the hypothesis for widespread practical use.

Heavy Rainfall Associated with Double Low-Level Jets over Southern China. Part II: Convection Initiation

Abstract Heavy rainfall that occurred at the south coast of China on 10–11 May 2014 was associated with a synoptic-system-related low-level jet (SLLJ) and a boundary layer jet (BLJ). To clarify the role of the double low-level jets in convection initiation (CI), we perform convective-permitting simulations using a nonhydrostatic mesoscale model. The simulations reproduce the occurrence location and mesoscale evolution of new convective cells as well as their small-scale wavelike structures at the elevated layers, which are generally consistent with radar observations despite some differences in their orientation. The nighttime BLJ over the northern South China Sea strengthens the convergence at ~950 hPa near the coast where the BLJ’s northern terminus reaches the coastal terrain. Meanwhile, the SLLJ to the south of the inland cold front provides divergence at ~700 hPa near the SLLJ’s entrance region. Such low-level convergence and midlevel divergence collectively produce strong mesoscale lifting for CI at the coast. In addition to the enhanced mesoscale lifting, the double low-level jets also provide favorable conditions for the superimposed small-scale disturbances that can serve as effective moistening mechanisms of the lower troposphere during CI. In a sensitivity experiment with coastal terrain removed, CI still occurs near the coast but is delayed and weaker compared to the control run. This latter experiment suggests that double low-level jets and their coupling indeed exert key effects on CI, while the BLJ colliding with terrain may enhance coastal convergence for amplifying CI. These findings provide new insights into the occurrence of coastal heavy rainfall in the warm sector far ahead of the fronts.

Characteristics of the Marine Boundary Layer Jet over the South China Sea during the Early Summer Rainy Season of Taiwan

Abstract The marine boundary layer jets (MBLJs) over the northern South China Sea during the early summer rainy season over Taiwan are analyzed using 5-yr (2008–12) National Centers for Environmental Prediction Climate Forecast System Reanalysis data with a 6-h interval. The MBLJ is distinctly different from the low-level jets associated with the subsynoptic frontal systems. During this period, the MBLJ events over the northern South China Sea mainly occur during the second half of the monsoon rainy season over Taiwan (after 1 June) and have a wind speed maximum around the 925-hPa level. The MBLJs are mainly related to the subsynoptic-scale pressure gradients related to a relatively deep mei-yu trough over southeastern China and a stronger-than-normal west Pacific subtropical high. Within the MBL, there is a three-way balance among pressure gradients, Coriolis force, and surface friction, with cross-isobar ageostrophic winds pointing toward the mei-yu trough throughout the diurnal cycle. At the jet core, the vertical wind profile resembles an Ekman spiral with supergeostrophic winds >12 m s−1 near the top of the MBL. The MBLJs are strongest at night and close to geostrophic flow in the late afternoon/early evening. This is because the friction velocity and ageostrophic wind decrease during daytime in response to mixing in the lowest levels. The MBLJs play an important role in horizontal moisture transport from the northern South China Sea to the Taiwan area. In the frontal zone, the moisture tongue extends vertically upward. The rainfall production is related to vertical motions in the frontal zone or localized lifting due to orographic effects.

Heavy Rainfall Associated with Double Low-Level Jets over Southern China. Part I: Ensemble-Based Analysis

AbstractHeavy rainfall occurred at both the inland frontal zone and coastal warm sector in southern China during 10–11 May 2014, which is a typical pattern in the early-summer rainy season. To clarify the key factors controlling the rainfall, we conduct an ensemble-based analysis using the operational global ensemble forecasts from ECMWF. The forecasts of frontal (warm sector) rainfall have a relatively small (large) spread and a small (large) bias of ensemble-mean amount, suggesting an obvious difference in the predictability. It is shown that double low-level jets (LLJs) in the southwesterly moist flow play a significant role in the heavy rainfall over southern China. The inland frontal rainband is closely related to the synoptic-system-related low-level jet (SLLJ) with maximum wind speed at 850–700 hPa, especially for its meridional wind component. The more intense cold front is accompanied by the stronger southwesterly SLLJ on the adjacent south side, favoring more precipitation near the front. The warm-sector heavy rainfall, a few hundred kilometers away from the front, is associated with the boundary layer jet (BLJ) at 925 hPa. The southerly BLJ occurs over the northern region of the South China Sea and reaches its maximum wind speed in the early morning. The variations of the BLJ are mainly induced by the surface low and related upper-level short-wave trough upstream. The large pressure gradient to the southeast of the surface low can accelerate the BLJ by increasing the geostrophic winds. The diurnal cycle of the low-level winds, seen in the climatology, also contributes in part to the development of the BLJ at night.

Fluid Dynamic Characterization of Transcatheter Aortic Valves Using Particle Image Velocimetry.

Transcatheter aortic valves provide superior systolic hemodynamic performance in terms of valvular pressure gradient and effective orifice area compared with equivalent size surgical bioprostheses. However, in depth investigation of the flow field structures is of interest to examine the flow field characteristics and provide experimental evidence necessary for validation of computational models. The goal of this study was to compare flow field characteristics of the three most commonly used transcatheter and surgical valves using phase-locked particle image velocimetry (PIV). 26-mm Edwards SAPIEN 3, 26-mm Medtronic CoreValve, and 25-mm Carpentier-Edwards PERIMOUNT Magna were examined in a pulse duplicator with input parameters matching ISO-5840, that is, heart rate of 70 beats/min, cardiac output of 5 L/min, and mean aortic pressure of 100 mm Hg. A 2D PIV system was used to obtain flow velocity and viscous shear stress fields during the entire cardiac cycle. In vitro testing showed that the mean transvalvular pressure gradient was lowest for SAPIEN 3, followed by CoreValve, and PERIMOUNT Magna surgical bioprosthesis. In addition, the viscous shear stress magnitude within the jet boundary layer was higher in PERIMOUNT Magna than CoreValve and SAPIEN 3 at the peak of the flow. However, the measured shear stress values were below the known threshold for platelet activation and red blood damage. Therefore, shear-induced platelet activation is unlikely to take place during systole in the three bioprosthetic heart valves. The PIV measurements can be used for verification and validation of computational simulations.

Computational and experimental investigation of fluidic thrust vectoring actuator

Fluidic thrust vectoring (FTV) control is an innovative technique employed to affect the pitch control of an air vehicle or an unmanned air vehicle in the absence of conventional control surfaces such as elevators. The main motivation in using FTV is to render the aircraft low observable. In this work, a relatively new concept called co-flow type of FTV concept is investigated. Wherein, a high velocity secondary jet is injected into the boundary layer of the primary jet causing deflection of main primary jet thereby enabling generation of pitch moment. Two sets of numerical simulations studies were undertaken, one for different ratios of Coanda surface radius (R) and primary height (hprim) while the other for different ratios of secondary gap height (∆h) and primary height (hprim). The insight gained from simulations guided the design of a working FTV test rig. A static test rig was manufactured where blower and a compressor were used to provide primary and secondary flows, respectively. Comparison of vectored jet behaviour predicted by computational fluid dynamics analyses is found to be in agreement with those obtained through experimentation.

Hydrodynamics around a shroud tube assembly of a fast breeder reactor

Control plug assembly of a liquid sodium cooled fast breeder reactor is partially submerged inside the liquid sodium coolant pool, free surface of which is blanketed with cover gas, mainly Argon to provide a non-reactive environment. It receives high velocity coolant flow from the fuel subassembly which travels through annular gap inside Control Safety Rod Driving Mechanism (CSRDM) assembly leading to swelling of free surface and gas entrainment inside the coolant pool. Entrained gas bubbles travel through different submerged components of the reactor and induces numerous complications including reactor power fluctuation, cavitation in inlet pumps and heat transfer inhibition in heat exchangers. Study of hydrodynamics around the shroud tube is crucial to examine cover gas entrainment inside the pool. The present study reports an experimental study on a 1:9 scale down model of CSRDM shroud tube assembly based on Froude number similarity. Eccentricity of the control rod inside the shroud tube is also an important parameter as temperature gradient along the CSRDM assembly leads to longitudinal thermal stress causing displacement of control rod from its center position in the shroud tube. Flow behavior around shroud tube, hump formation at the axial exit of shroud tube, air entrainment inside coolant pool have been reported for various parameters viz. inlet flow rate (qi), free surface height (hf) and eccentricity of central rod (e). Dye visualization, Schlieren visualization, Bulk visualization have been carried out and digital image processing techniques have been adopted for quantification of hump parameters and entrained air fraction inside the coolant pool.The axial flow from the exit of the shroud tube impinges on the free surface like a wall jet. At low Froude number, the impinging jet flow travels radially outward on the interface like a wall jet boundary layer. The shear of the free surface flow drags the jet like flow from the pores upward leading to mixing between the vortices inside the shear layer and the free vortices from the pores of the shroud tube. At high Froude number, the impinging jet like flow penetrates through the interface leading to hump formation. The downward motion of the hump reduces the radial free surface flow and blankets the radial flow from the pores of the shroud tube. The eccentricity of the central rod leads to asymmetric axial flow from the shroud tube and thus the resulting hump becomes asymmetric due to impingement of asymmetric jet. Therefore, the impingement angle of the downward hump motion becomes different at both sides of the shroud tube with asymmetric flow field and bubble formation process inside the liquid pool. However, the synchronization between the hump unsteadiness and the surface wave motion leads to mixing of air bubbles inside the liquid pool. Average entrained air fraction increases with increase in inlet flow rate and decreases with increase in free surface height.

Interaction between plasma synthetic jet and subsonic turbulent boundary layer

This paper experimentally investigates the interaction between a plasma synthetic jet (PSJ) and a subsonic turbulent boundary layer (TBL) using a hotwire anemometer and phase-locked particle imaging velocimetry. The PSJ is interacting with a fully developed turbulent boundary layer developing on the flat wall of a square wind tunnel section of 1.7 m length. The Reynolds number based on the freestream velocity (U∞ = 20 m/s) and the boundary layer thickness (δ99 = 34.5 mm) at the location of interaction is 44 400. A large-volume (1696 mm3) three-electrode plasma synthetic jet actuator (PSJA) with a round exit orifice (D = 2 mm) is adopted to produce high-speed (92 m/s) and short-duration (Tjet = 1 ms) pulsed jets. The exit velocity variation of the adopted PSJA in a crossflow is shown to remain almost identical to that in quiescent conditions. However, the flow structures emanating from the interaction between the PSJ and the TBL are significantly different from what were observed in quiescent conditions. In the midspan xy plane (z = 0 mm), the erupted jet body initially follows a wall-normal trajectory accompanied by the formation of a distinctive front vortex ring. After three convective time scales the jet bends to the crossflow, thus limiting the peak penetration depth to approximately 0.58δ99. Comparison of the normalized jet trajectories indicates that the penetration ability of the PSJ is less than steady jets with the same momentum flow velocity. Prior to the jet diminishing, a recirculation region is observed in the leeward side of the jet body, experiencing first an expansion and then a contraction in the area. In the cross-stream yz plane, the signature structure of jets in a crossflow, the counter-rotating vortex pair (CVP), transports high-momentum flow from the outer layer to the near-wall region, leading to a fuller velocity profile and a drop in the boundary layer shape factor (1.3 to 1.2). In contrast to steady jets, the CVP produced by the PSJ exhibits a prominent spatiotemporal behaviour. The residence time of the CVP is estimated as the jet duration time, while the maximum extent of the affected flow in the three coordinate directions (x, y, and z) is approximately 32D, 8.5D, and 10D, respectively. An extremely high level of turbulent kinetic energy production is shown in the jet shear-layer, front vortex ring, and CVP, of which the contribution of the streamwise Reynolds normal stress is dominant. Finally, a conceptual model of the interaction between the PSJ and the TBL is proposed.

The flow external to a rotating torus

Imparting a sudden rotation to a torus (or other symmetric smooth object) in an otherwise quiescent, viscous fluid serves to generate boundary layers at the object’s surface. These boundary layers are known to exhibit a finite-time singularity at the equator which manifests in a thickening of the boundary layer and subsequent development of an equatorial jet. Here we consider the post-collision flow dynamics, demonstrating that the equatorial jet serves to shed a finite amplitude toroidal vortex pair. The radial jet is also shown to develop an absolute instability at suitably high Reynolds numbers.

A Review on Empirical Correlations for Jet/Spray Trajectory of Liquid Jet in Uniform Cross Flow

The empirical correlations for the prediction of jet/spray penetration of liquid jet in subsonic uniform crossflow are reviewed in this study. Considerable number of empirical correlations had been proposed by many investigators. It has generally known that the jet/spray trajectory of a liquid jet in a cross-flow is a function of the liquid to air momentum flux ratio and the normalized distance in the airstream direction from the injector. However, several researchers incorporated the Weber number, liquid-to-water or air viscosity ratio, pressure ratio or Reynolds number, temperature ratio in the empirical correlations. Two different classification methods of correlations, i.e. classification based on mathematic functional form and classification based on flow regime, are introduced in this study. The one classification of existing correlations based on functional form includes correlations in a power-law, logarithmic, and exponential forms, respectively. The other classification of previous correlations based on flow regime includes one, two and three regime, correlations. Correlations in a power-law functional form can be further divided into three groups such as momentum flux ratio, Weber number and other parameters forms. Correlations in logarithmic functional form can be also grouped as momentum flux ratio and Weber number forms. Most of the evaluation studies reported the significant discrepancies of predicted values by the existing correlations. The possible reasons for discrepancies will be summarized as measurement technique, assumptions made in defining terms in the liquid to air momentum flux ratio, difficulties in defining the boundaries of the liquid jets, turbulence level in the core and boundary layer of incoming jet and gas flows, nozzle/injector geometry and its position in the crossflow. However, it can be found from the several evaluation studies that the power-law functional form with momentum flux ratio and two regimes correlations provided relatively the best fit to experimental data.

DeepChandraobservations of Pictor A

We report on deep Chandra observations of the nearby broad-line radio galaxy Pictor A, which we combine with new Australia Telescope Compact Array (ATCA) observations. The new X-ray data have a factor 4 more exposure than observations previously presented and span a 15-year time baseline, allowing a detailed study of the spatial, temporal and spectral properties of the AGN, jet, hotspot and lobes. We present evidence for further time variation of the jet, though the flare that we reported in previous work remains the most significantly detected time-varying feature. We also confirm previous tentative evidence for a faint counterjet. Based on the radio through X-ray spectrum of the jet and its detailed spatial structure, and on the properties of the counterjet, we argue that inverse-Compton models can be conclusively rejected, and propose that the X-ray emission from the jet is synchrotron emission from particles accelerated in the boundary layer of a relativistic jet. For the first time, we find evidence that the bright western hotspot is also time-varying in X-rays, and we connect this to the small-scale structure in the hotspot seen in high-resolution radio observations. The new data allow us to confirm that the spectrum of the lobes is in good agreement with the predictions of an inverse-Compton model and we show that the data favour models in which the filaments seen in the radio images are predominantly the result of spatial variation of magnetic fields in the presence of a relatively uniform electron distribution.

Influence of Exhaust Nozzle Geometry on the Jet Potential Core Development

In this paper, a numerical simulation was performed on a scale turbofan engine nozzle to asses the influence of two nozzle configurations over the flow performance while the nozzle is situated at a certain distance from the ground. The turbulence model chosen for this numerical simulation was SST k-ω to capture boundary layer detachment and jet attachment to the ground. For this analysis two different computational domains where considered, while for the third case, boundary conditions for secondary inlet where modified. To assess the impact of these geometry changes a comparison between cases is made at different location in the domain.

Displaced logarithmic profile of the velocity distribution in the boundary layer of a turbulent flow over an unbounded flat surface

It is shown that the Reynolds equations for a turbulent flow over an unbounded flat surface in the presence of a constant pressure-gradient lead to a displaced logarithmic profile of the velocity distribution; the displaced logarithmic profile is obtained by assuming a constant production rate of turbulence energy. The displacement height measured on the (vertical) axis perpendicular to the surface is either positive or negative. For a positive displacement height the boundary layer exhibits an inversion, while for a negative displacement height the boundary layer is a direct one. In an inversion boundary layer the logarithmic velocity profile is disrupted into two distinct branches separated by a logarithmic singularity. The viscosity transforms this logarithmic singularity into a sharp edge, governed by a generalized Reynolds number. The associated temperature distribution is calculated, and the results are discussed in relation to meteorological boundary-layer jets and stratified layers. The effects of gravitation and atmospheric thermal or fluid-mixture concentration gradients (“external forcings”) are also considered; it is shown that such circumstances may lead to various modifications of the boundary layers. A brief presentation of a similar situation is described for a circular pipe.

The influence of a pressure wavepacket's characteristics on its acoustic radiation.

Noise generation by flows is modeled using a pressure wavepacket to excite the acoustic medium via a boundary condition of the homogeneous wave equation. The pressure wavepacket is a generic representation of the flow unsteadiness, and is characterized by a space envelope of pseudo-Gaussian shape and by a subsonic phase velocity. The space modulation yields energy in the supersonic range of the wavenumber spectrum, which is directly responsible for sound radiation and directivity. The influence of the envelope's shape on the noise emission is studied analytically and numerically, using an acoustic efficiency defined as the ratio of the acoustic power generated by the wavepacket to that involved in the modeled flow. The methodology is also extended to the case of acoustic propagation in a uniformly moving medium, broadening possibilities toward practical flows where organized structures play a major role, such as co-flow around cruising jet, cavity, and turbulent boundary layer flows. The results of the acoustic efficiency show significant sound pressure levels, especially for asymmetric wavepackets radiating in a moving medium.

Numerical Simulations of the Boundary Layer Jet off the Southeastern Coast of China

Abstract A strong coastal boundary layer jet (CBLJ) (~8 m s−1) off the southeastern coast of China (around 28°N, 122°E) is found from the July 2006–11 hourly model data simulated by the Advanced Research Weather Research and Forecasting Model (WRF-ARW) with a 9-km horizontal grid. The southerly CBLJ has a jet core at the 925-hPa level, located along the western periphery of the west Pacific subtropical high (WPSH). The CBLJ is mainly contributed by large-scale enhancement by diurnal forcing and orographic effects by the coastal terrain along the southeastern China coast and the terrain of Taiwan. Although the geostrophic winds offshore are faster in the afternoon due to the larger east–west pressure gradient caused by land surface heating over the China plain, the CBLJ has a nocturnal (~0200 LST) maximum. In the afternoon hours, easterly ageostrophic winds driven by differential land–sea thermal heating develop at low levels. After sunset, with the disappearance of land surface heating, the ageostrophic winds offshore veer southward by the Coriolis force and combine with the southerly geostrophic flow resulting in a nocturnal maximum in the CBLJ. Furthermore, from two model sensitivity experiments (NoTW and LowFJ), it is apparent that the terrain of Taiwan and Fujian exerts a secondary influence (1–2 m s−1) on the strength of the CBLJ. The orographic blocking by the terrain of Taiwan and Fujian is more significant with a larger (~1 m s−1) southerly wind component north of the Taiwan Strait at night than in the afternoon hours.

Characteristics and Calculation of Cavitation Mixers

It is shown that one of the most efficient ways to obtain emulsion is cavitation treatment of the mixed stream in the jet boundary layer. The authors offer a model for calculating the operational process in the hydrodynamic mixer with multiple-jet nozzle as agitator of cavitation, based on hydrodynamic equations and data of experimental research on jet pumps. There has been considered and analyzed the characteristic of the cavitation mixer, which shows how relative loss of total stream pressure depends on relative nozzle square, and hydraulic resistance coefficient of flow-part elements. It is shown that gradual reduction of hydraulic resistance coefficient allows to decrease considerably the loss of total stream pressure. Besides, there exists the range of optimal relative square values where losses of total pressure are minimized. If the elements of the mixer flow-part are made hydraulically proper then the optimal values of the nozzle relative square are 0,66…0,76, whereas minimum losses of relative pressure don’t exceed 0,22.

Fluid flow of a wall jet impinging a hot obstacle

A numerical study is performed in order to investigate the effects of the inlet flow structure on the flow and heat transfer characteristics in the reattachment zones over open cavity. Indeed, two inlet flow configuration are tested ; a turbulent wall jet which has a particular structure with two sources of turbulence production (the first is due to the shear flow associated to the inner layer characterized by small scale and second one is of the free shear jet flow with large turbulence scales) and a free boundary layer flow .The inner region of these two flows is similar, but their external regions are extremely different. The separating and reattaching flow phenomena are of particular interest in engineering fields. The numerical results of the analyses the loca convective heat transfer. The Nusselt number is more important and decreases immediately downstream the reattachment under the wall jet inlet flow. This detail may be explained from a dynamical point of view; the turbulent energy is more important but in small area around the each reattachment zone. The local Nusselt number increases when the Reynolds numbers augments. The evolution of local Nusselt , depends on incoming flow configuration. For the two configuration of incoming flow (Boundary layer or Wall jet), the distribution of mean Nusselt number is correlated according with some problem parameters.

Numerical Study of Heat Transfer and Separated Flow over Rectangular Obstacle in Jet

This paper is about a separated reattaching flow over a hot rectangular obstacle. Two types of incoming flow are examined in order to show the influence of the external zone of the flow on the reattachment process. It comes about due to a wall jet and a boundary layer. The inner region of these two flows is similar, but their external regions are extremely different. The separating and reattaching flow phenomena are of particular interest in engineering fields such as for an aeronautical application. Wall jet flow over an obstacle occurs in many engineering applications such as environmental discharges, heat exchangers, fluid injection systems, cooling of combustion chamber wall in a gas turbine, automobile design, and others. In electronics cooling, the prediction of the Nusselt number distribution along the obstacles is necessary before the design of the apparatus. For a heated obstacle at a constant temperature, T = 350 K and an aspect ratio of 10 (L = 10 H), the problem parameters are: (a) jet exit Reynolds number (Re) ranged from 1000 to 50000, (b) incoming flow configuration (boundary layer and wall jet). The ratio between the thickness of the nozzle (b) to the obstacle height (H) are examined simultaneously. The formulation is based on the SST k–ω turbulence model. The results show that the increasing of nozzle thickness; enhances the heat transfer and considerably modifies the stagnation point location. The highest incoming flow momentum provides the greatest values of average Nusselt number. Such as the boundary layer case in comparison with the wall jet cases. The average Nusselt number is correlated according to problem parameters .