Turbulent Jet Research Articles

Experimental Study of the Behavior of Horizontally Buoyant Turbulent Jet Flames in Acoustic Waves

Natural gas is most commonly transported by pipeline. However, leaks sometimes occur during transport, often leading to jet fires that cause substantial economic damage and property damage. It is therefore crucial to improve the efficiency of jet fire suppression. This paper focuses on the change of flame morphology of horizontal jet fires under different boundary conditions (acoustic pressure, frequency and jet exit velocity) and experimentally analyses the horizontal, vertical and trajectory length variation laws of the flame. Then a prediction model relating the horizontal length, vertical length and trajectory length of the horizontal jet flame under the action of acoustic waves is established.

Visualization of the rotational and irrotational motions in a temporally evolving turbulent plane jet

Visualization of the rotational and irrotational motions in a temporally evolving turbulent plane jet

Flow measurements of jet impingement upon a semicylinder with crossflow

In this work, time-resolved particle image velocimetry (TR-PIV) measurements have been carried out to investigate the structural features of a submerged transverse round liquid turbulent jet discharged into a confined laminar crossflow. The duct Reynolds number based on crossflow velocity is fixed at Re=3000, and the impinging jet is directed to a semicylindrical concave surface located in one of the walls of a vertical square duct. The spatial development and flow dynamics are analyzed along several orthogonal planes parallel/perpendicular to the jet axis for jet Reynolds numbers based on the jet exit diameter of Rej=3000, 6000 and 9000 (jet-to-crossflow velocity ratios of r=3.27, 6.53 and 9.80), respectively. For this purpose, mean and ensemble-averaged velocity and vorticity distributions, turbulent statistics, and Reynolds shear stresses are obtained for various injection rates. Spectral analysis reveals the shedding frequencies of the wake vortices, and the pairing and breakup processes of the evolving large-scale coherent structures have been related to the measured wake Strouhal numbers. Our results indicate that due to the curvature of the target surface and the upwash of the jet impact, the size of coherent structures decreases with increase in the value of Rej. Proper orthogonal decomposition (POD) of the flow using the snapshot method is applied to extract the dominant features of the turbulent flow. It is observed that at the symmetry plane and for Rej=3000, 6000 and 9000, the energy collected by the first two dominant eddies contribute to 14.98%, 18.68%, and 17.89% of the turbulence kinetic energy, respectively. Our results show that the evolution of the time-resolved temporal coefficients of degenerate pairs of modes (1, 2) represent the flapping motion of the jet. Moreover, the amplitude of the oscillations of the flapping jet and the complexity of the flow structure increase for increasing values of Rej.

A Database for Reduced-Complexity Modeling of Fluid Flows

We present a publicly accessible database specifically designed to aid in the conception, training, demonstration, evaluation, and comparison of reduced-complexity models for fluid mechanics. Availability of high-quality flow data is essential for all of these aspects of model development for both data-driven and physics-based methods. The current database is unique in that it has been curated with this need in mind. The database contains time-resolved data for six distinct datasets: a large eddy simulation of a turbulent jet, direct numerical simulations of a zero-pressure-gradient turbulent boundary layer, particle-image-velocimetry measurements for the same boundary layer at several Reynolds numbers, direct numerical simulations of laminar stationary and pitching flat-plate airfoils, particle-image-velocimetry and force measurements of an airfoil encountering a gust, and a large eddy simulation of the separated, turbulent flow over an airfoil. These six cases span several key flow categories: laminar and turbulent, statistically stationary and transient, tonal and broadband spectral content, canonical and application-oriented, wall-bounded and free-shear flow, and simulation and experimental measurements. For each dataset, we describe the flow setup and computational/experimental methods, catalog the data available in the database, and provide examples of how these data can be used for reduced-complexity modeling. All data can be downloaded using a browser interface or Globus. Our vision is that the common testbed provided by this database will aid the fluid mechanics community in clarifying the distinct capabilities of new and existing methods.

Ammonia-hydrogen engine with reactivity-controlled turbulent jet ignition (RCTJI)

Ammonia (NH3) is a promising fuel for engine carbon neutrality. However, the terrible combustion characteristics substantially restrain the application of NH3 in internal combustion engines (ICE). Hydrogen addition and pre-chamber turbulent jet ignition (TJI) show outstanding abilities to solve the difficult ignition and low flame velocity for ammonia combustion. At present work, a concept of reactivity-controlled TJI (RCTJI) with hydrogen fuel is proposed, and the combustion characteristics of the ammonia-hydrogen engine are investigated. The present study proposes two operating modes of the RCTJI ammonia-hydrogen engine. The controllable pre-chamber reactivity is achieved by varying the hydrogen concentration and/or adjusting the quantity of the pre-chamber mixture. Then, the effects of the pre-chamber properties regarding the pre-chamber nozzle diameter, per-chamber operating mode, and pre-chamber mixture reactivity on the engine performance are analyzed. The results show that adjusting the mixture reactivity in the pre-chamber can effectivity control the ignition ability and engine performance. The better performance of the RCTJI ammonia-hydrogen engine is obtained under the conditions of per-chamber with a 4 mm hole size and hydrogen fuel, and it can further be optimized by operating the pre-chamber in Mode 2 with an extra scavenging process. An operation strategy of the pre-chamber for the RCTJI ammonia-hydrogen engine is proposed: the RCTJI pre-chamber is suggested to operate under Mode 2 and achieve the first scavenging process by stoichiometric hydrogen/air mixture, and the injection quantity of scavenging gas in the pre-chamber should be controlled in the range of 1.0 Mt–2.5 Mt. At the boosting conditions, the power performance and fuel economy of the RCTJI ammonia-hydrogen engine are optimized effectively. The indicated mean effective pressure (IMEP) increases from 6.3 bar to 10.0 bar at λ = 1.0 as the intake pressure increases from 1.0 bar to 1.4 bar. The optimum fuel consumption rate is obtained at the lean condition of λ = 1.4, achieving a 13.3% reduction of the indicated specific fuel consumption (ISFC).

X-ray radiography 4D particle tracking of heavy spheres suspended in a turbulent jet

The suspension of a heavy sphere by an upward jet is a classical fluid mechanics experiment to demonstrate the fluid forces acting on an object. In the range of the parameter space where the sphere can be suspended, the dynamics can either be regular, i.e., with oscillations around an equilibrium position, or chaotic, with extreme events leading to large deviations from that equilibrium region. The existence and characteristics of suspension regimes of several heavy spheres in such flow configurations remain open questions. Spheres compete for the equilibrium position and come very close to each other, resulting in large local particle concentrations that prevent direct imaging. Relatively high speed X-ray radiography along with the radioSphereanalysis technique is leveraged here to study the time-resolved 3D trajectory of each individual sphere in a vertical jet. radioSphereis an X-ray analysis method that retrieves the 3D information out of a single 2D radiography using a priori knowledge of the imaging geometry (E. Andò et al., 2021), which due to the imaging modality imposes no limitations on the optical properties of the water. The 3D ＋ time kinematics yield the evolution of the statistics of the position and velocity of the spheres as a function of the number of spheres and for two jet Reynolds numbers. Drastic changes in behavior occur when many spheres are present, leaving a clear signature on the temporal dynamics and on the exploration of the flow volume, where spheres can remain on the bottom of the vessel for long periods of time, resulting in only partial suspension. In addition to the suspension capacity, the interactions between spheres are explored with statistics of pair separation distances, which, together, allow for quantitative arguments to introduce suspension regimes of a collection of spheres in an upward vertical jet.

Research on Characteristics of Hydrogen Dynamic Leakage and Combustion at High Pressure

Hydrogen is promoted as an alternative energy given the global energy shortage and environmental pollution. A scientific basis can be provided for the safe use and emergency treatment of hydrogen based on hydrogen leakage and combustion behavior. This study examined the stagnation parameters of dynamic hydrogen leakage and flame propagation in turbulent jets under normal temperatures and high pressure. Based on van der Waals’ equation of state for gas, a theoretical model for completely predicting stagnation parameters, outlet gas velocity, and flow rate changes in the process of high-pressure hydrogen leakage could be proposed, and the calculation result of this model was compared with the experimental result, with an error within ±10%. The progression and propagation of the flame in turbulent jets after ignition were recorded using the background-oriented schlieren image technology, and the propagation speed of flame from the ignition position downward and upward was calculated. Moreover, the influence of initial pressure, nozzle diameter, and ignition position on the flame propagation process and propagation speed was analyzed.

Experimental characterization of the turbulent intake jet in an engine flow bench

The turbulent intake flow of an optically accessible internal combustion engine is modeled using an air flow bench to reduce the complexity in the number of variables inherent within engine flows. By removing the piston and introducing a new optically accessible housing and outlet channel, the flow bench design simulates engine flows in the region just downstream of the intake valves and offers the possibility to measure and calculate quantities that would be difficult or impossible to obtain in the unsteady environment of a dynamic engine. Velocity data obtained via high-speed particle image velocimetry of the flow bench in the symmetry and valve planes are compared with data from a base operating condition of the motored engine at an intake pressure of 0.95 bar and a speed of 800 rpm at - 270°CA (270 crank-angle-degrees before compression top dead center), beginning with stationary valves at the corresponding valve lift of - 270°CA, then with moving valves. Analysis of the intake jet turbulence for increasing mass flow rates reveals a coherent flapping of the jet at a frequency of 752.5 Hz for only the 100% mass flow rate case. The vortex shedding frequency of the valve stem is estimated to being in the range of 634–799 Hz, indicating a possible link between the coherent jet flapping and the vortex shedding surviving the acceleration through the valve gap. Through comprehensive analysis, this study provides valuable validation data and insight into the intake flows of internal combustion engines.

Modelling the response of a turbulent jet flame to acoustic forcing in a linearized framework using an active flame approach

This study performs a linear mean field analysis of a turbulent reacting methane-air jet flame, with the goal of predicting the response of the reacting flow to upstream acoustic actuation. Unlike previous studies, this work develops and applies an active flame approach by taking the heat release oscillations of the flame resulting from the acoustic fluctuations into account. For an active flame approach in the linear mean field analysis, a linearized combustion model is necessary. Linearizing Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) combustion models leads to closure problems, making their application in this context troublesome, whereas Reynolds-averaged Navier Stokes (RANS) combustion models prove to circumvent this problem making them suitable candidates for this purpose. The RANS combustion models are linearized around the temporal mean state variables of the turbulent jet flame, which is obtained by LES. An a priori analysis shows that a linearized RANS–Eddy Break Up (EBU) model is the best suited among all investigated combustion models for the investigated set-up and reproduces with high accuracy the fluctuations in reaction rate obtained in the LES. Furthermore, the linearized governing equations of the flow including the linearized EBU model for the reaction rate are solved for incoming acoustic perturbations. The response modes show that the reaction rate oscillations are caused by Kelvin–Helmholtz vortex rings, which perturb the jet flame. The results are in good agreement with the LES simulations in terms of the mode shapes of both reaction rate and velocity fluctuations. This study represents a basis for linear mean field analysis of turbulent flames and monolithic modelling approaches for thermoacoustic instabilities in gas turbine combustors.

The characteristics of gas-liquid dispersive mixing and microbubble generation in turbulent adjustable jet flow field

In this study, the gas-liquid two-phase mixing process and the microbubbles formation process in a jet flow field has been investigated by using a self-designed on-line measurement system for measuring bubble generation characteristics and the Volume of Fluid (VOF) model in numerical simulation methods for analyzing flow field distribution characteristics. The effect of turbulence intensity on the dynamic size distribution of microbubble has been considered. The characteristics and duration of the three stages during the bubble breaking process, namely, surface oscillation stage, surface tension stage and fracture stage, were analyzed. The results show that the increase of turbulence intensity in jet flow will further promote the imbalance between the external deformation force and the surface tension resisting the deformation of the bubble, and promote the breaking probability of bubble. However, when the bubble breaks to a sufficiently small size, the surface tension against bubble deformation will increase sharply, the surface free energy needed to overcome for bubble breakage is very large, and the breakage probability of bubble will significantly decrease. Compared with the breaking process of bubbles, the increase in turbulence intensity will greatly promote the bubble coalescence process, which will ultimately become the main reason for affecting the bubble size distribution. Moreover, the influence of flow field distribution characteristics on bubble size distribution and average bubble size change is analyzed by using Population Balance Model.

Characteristics of ethylene and methane combustion in a range of high temperature and low oxygen environments

New understanding of turbulent jet flames of natural gas, and blends of natural gas with ethylene (C2H4), issuing into a range of preheated coflowing oxidisers with reduced oxygen (O2) concentrations are reported. Comparisons are made for coflow O2 concentrations of 3%, 4%, 5%, 6%, 9% and 11% and coflow temperatures of 1250 K, 1315 K and 1385 K. Instantaneous and simultaneously planar imaging measurements of temperature, hydroxyl radicals (OH) and formaldehyde (CH2O) were taken at eight locations ranging from 9 mm to 75 mm downstream of the jet exit plane. The experimental data is supplemented with chemical reaction modelling. It is shown that increasing the proportion of C2H4 in the fuel supply resulted in an increase in the flame front temperature. At 3% O2, CH2O signal did not very between the three fuels containing C2H4, whilst at 9%, the signal increased with increasing C2H4. OH number density was highest for a blend of 66% NG and 33% C2H4. The fuel composition made little effect on the jet spread rate. Reaction modelling found evidence of changes in the reaction process, both in the suppression of reactions with different fuels, and in the suppression of reactions, and the locations they occur, with reducing O2 concentrations. Reaction modelling also found a significant decrease in ignition delay when C2H4 was present in the fuel mixture, and an increase in ignition delay as all four fuels transition to MILD combustion.

DNS study on reactivity stratification with prechamber H[formula omitted]/air turbulent jet flame to enhance NH[formula omitted]/air combustion in gas engines

The present study investigates turbulent flame dynamics and pollutant emission characteristics in a prechamber/main chamber system. A H2/air turbulent jet flame issued from the prechamber penetrates into the NH3/air mixture found in the main chamber. Recent experimental studies have demonstrated that this configuration is very promising for future NH3 combustion in gas engines. In the present work, 3D direct numerical simulations (DNS) with detailed chemistry have been carried out in the above configuration. The dynamics of the turbulent premixed flame in the prechamber (flame thickness, flame propagation speed) and the structure of the turbulent stratified flame in the main chamber are investigated. It is found that the stratified flame thickness is becoming thicker as the flame propagates within the NH3/air mixture. The flame displacement speed is slowing down in a first phase, before becoming faster again after jet-induced turbulence starts to decay. A chemical explosive mode analysis (CEMA) has been done to distinguish between ignition, flame propagation, and local extinction events both for the premixed flame in the prechamber and the stratified flame in the main chamber. The temporal evolution of the identified modes are consistent with the flame dynamics and help to explain the later increase in flame displacement speed. NO emission characteristics in the main chamber have also been investigated. The NO production speed first increases, reaches a plateau, before being reduced during later flame propagation; stratification is important to explain the NO emission characteristics. Compared to the laminar NH3/air flame, the NO production speed is obviously larger in the present configuration, mainly due to the reduced contribution of the NO destruction reactions in the fuel pathway. Compared to premixed NH3/H2/air flames with H2 volume ratios found in practical systems (typically ≥ 0.4), the NO production speed is lower in the present configuration, demonstrating its superiority for practical applications. Finally, conventional heat release rate (HRR) markers are evaluated for the stratified flame. They approximate quite well the general structure of the flame front, but lead to noticeable quantitative errors.

Multi-scalar mixing in turbulent coaxial jets

Although natural and industrial flows often transport and mix multiple scalars, relatively few studies of turbulent multi-scalar mixing have been undertaken. In the present work, a novel three-wire thermal-anemometry-based probe – capable of simultaneously measuring velocity, helium concentration and temperature – is used to investigate the evolution of multiple scalars ($\phi _1$,$\phi _2$,$\phi _3$) and velocity in turbulent coaxial jets. The jets consist of (i) a centre jet containing a mixture of helium and air ($\phi _1$), (ii) an annular jet containing pure (unheated) air ($\phi _2$) and (iii) a coflow of (pure) heated air ($\phi _3$). Axial measurements are made at three different momentum flux ratios ($M=0.77, 2.1, 4.2$). Increasing$M$was observed to result in complex, competing effects. Larger momentum flux ratios cause the potential core of the centre jet to decrease in size, greater scalar fluctuations and more rapid correlation of$\phi _1$and$\phi _2$. However, at the same time, certain statistics, including those describing the velocity field, evolve more slowly. Moreover, the flow near the beginning of the fully merged region appears to be less mixed at higher values of$M$. The present work finally demonstrates that differences can be observed in the evolution and mixing of coaxial jets between those in which$M<1$and those in which$M>1$, thereby presenting an opportunity by which the mixing process in coaxial jets may be controlled.

Research on the structure of pre-chamber and jet orifice of a turbulent jet ignition rotary engine fueled with methanol/gasoline blends

This study used both methanol fuel and turbulent jet ignition (TJI) mode to improve the combustion and emission performance of a gasoline rotary engine (RE). Further, in order to research the combustion process of the turbulent jet ignition rotary engine (TJI-RE) fueled with methanol/gasoline blended fuel in depth, the experimental bench and numerical simulation model were established respectively. Moreover, the reliability of the numerical simulation model was verified by the experiments. Eventually, based on the numerical simulation model, the effects of the volume ratio of pre-chamber (VR-PC) and the length diameter ratio of jet orifice (LDR-JO) on the in-cylinder flame propagating were studied. The study results showed that for any fixed LDR-JO, increasing VR-PC could provide higher ignition energy for the cylinder.But the timing of the jet flame entering the cylinder, meanwhile, would be delayed. Therefore, considering the “trade-off” relationship between ignition energy and the timing of jet flame entering the cylinder, VR-PC is recommended to be 2.2%. For any fixed VR-PC, increasing LDR-JO could increase the injection speed of jet flame. But the cross-sectional area of the jet flame at the outlet of the jet orifice, meanwhile, would become smaller. Therefore, considering the “trade-off” relationship between the injection speed of jet flame and the cross-sectional area of the jet flame at the outlet of the jet orifice, LDR-JO is recommended to be 2.5. Additionally, for TJI-RE fueled with methanol/gasoline blended fuel, the higher the in-cylinder peak pressure, the more sufficient the combustion, and the lower the CO emission. And the trend of NO emission was opposite to that of CO emission.

Heat transfer on a flat wall due to a rectangular turbulent jet

We present Large Eddy Simulation (LES) results of heat transfer and flow evolution of a turbulent two-dimensional rectangular jet of air, of height H, impinging upon a flat wall. Rectangular jet is quasi-two dimensional, i.e. planar jet with infinite slot-width. Exit of jet is set at four distances, D, from wall, D = 4H, 3H, 2H, H. Distance of slot exit to wall modifies flow evolution, reported as mean and instantaneous, compared to experimental data. In mean flow Undisturbed Region of Flow, URF, and, in instantaneous flow, Negligible Disturbances Flow, NDF, and Small Disturbances Flow, SDF, are reported for the various distances D/H. In order to evaluate influence of flow parameters on heat transfer and flow evolution, two levels of turbulence are imposed on slot jet exit, i.e. 1% and 6%. The level of turbulence modifies heat transfer results, as far as convective heat transfer and Nusselt number are concerned. The shape of Nusselt number distribution along impinged wall is different according to level of turbulence. The paper presents a very good comparison with experimental Nusselt numbers, for the first time in literature.

Numerical investigation of powder aerosolization in a mining rock dust dispersion chamber

We have conducted numerical simulations of dust dispersion within the NIOSH Rock Dust Dispersion Chamber. The apparatus consists of a low-speed background ventilation flow down a long box in which is placed a tray containing a rock dust powder. A nozzle upstream of the tray introduces a short pulse of a turbulent horizontal jet flow just above the powder surface. We have utilized an incompressible Reynolds-Averaged Navier-Stokes k-ω model for the turbulent flow; particles are incorporated within a one-way Euler-Lagrangian formalism. The Rock Dust Dispersion Chamber ventilation flow exhibits a recirculation zone just above the powder-containing tray. Aerosolization proceeds via the interplay of the jet pulse flow with the background recirculation flow. The air flow is not well-mixed. The aerosolized dust is convected as a concentration cloud downstream towards the detection zone. For larger particles, gravitational settling depletes the convected cloud, so the instrument behaves as a horizontal elutriator. The instrument is robust with respect to misalignment of the jet nozzle. However, reduced streamwise drift velocity allows mixing to disperse the optically detected dust cloud concentration pulse. Our large particle simulation results compare favorably with published experimental results for large, polydisperse calcium carbonate rock dust.

Investigation of the effects of the scavenged prechamber turbulent jet ignition on the carbon dioxide diluted combustion

低碳燃烧概念的出现使得内燃机节能减排势在必行。废气再循环稀释燃烧作为一种提高热效率、降低排放的技术手段，有很大的应用价值。本文针对废气稀释下燃烧不稳定问题，提出了一种扫气式TJI装置。基于可视化定容燃烧弹研究了火花塞点火SI、被动式TJI和扫气式TJI在不同CO2浓度下的射流及火焰发展过程。研究发现TJI能够形成较强的湍流燃烧，相较于SI有着更快的燃烧速率。随着二氧化碳浓度的升高，火焰传播速度下降。TJI的射流出现时刻大幅推迟、射流强度逐渐降低，主燃室燃烧速率下降。通过对预燃室进行主动扫气可以改善预燃室内混合气状态，使得预燃室混合气在点火后燃烧速度加快。且射流强度不受二氧化碳浓度的影响，从而加快主燃室内的燃烧，拓展二氧化碳掺混极限。预燃室内当量比为1时射流强度最大。扫气模式下，二次扫气能更彻底地改善预燃室内混合气状态。相较于一次扫气更能提高射流强度，从而加快主燃室内燃烧。采用二次扫气策略可以提升主燃室稳定燃烧二氧化碳浓度极限至30%。

Numerical investigation on conjugate behavior of heat transfer and its augmentation in a turbulent wall-jet flow on a heated plate in motion

The present research involves a computational investigation by adopting a conjugate technique in a turbulent wall jet flow on a moving plate heated isothermally at the bottom. The low-Reynolds-number YS model is adopted for the simulation to predict the thermal and fluid behavior in the near wall regime. The wall jet enters a quiescent environment of Prandtl number of 7 at a constant Reynolds number of Re = 15000 at the inlet. The thermal parameters considered for observing the thermal behavior are solid-fluid conduction ratio ( K ) , plate-jet thickness ratio ( S ) , and plate to jet velocity ratio ( U p ) . The temperature distributions in the plate domain, temperature at the solid-fluid interface, local Nusselt number, and average Nusselt number provided evidence of the effects of plate movement in the present cases. The plate motion strongly influences the distribution of the local and the averaged Nusselt number along with the temperature at the interface. The average Nusselt number calculated suggests that plate motion is crucial in enhancing heat transfer rate.

Effect of pre-chamber geometrical parameters and operating conditions on the combustion characteristics of the hydrogen-air mixtures in a pre-chamber spark ignition system

The pre-chamber spark ignition system is a promising advanced ignition system adopted for lean burn spark ignition engines as it enables stable combustion and enhances engine efficiency. The performance of the PCSI system is governed by the turbulent flame jet ejected from the pre-chamber, which is influenced by the pre-chamber geometrical parameters and the operating conditions. Hence, the current study aims to understand the effects of pre-chamber volume, nozzle hole diameter, equivalence ratio, and initial chamber pressure on the combustion and flame jet characteristics of hydrogen-air mixture in a passive PCSI system. Pre-chamber with different nozzle hole diameters (1 mm, 2 mm, 3 mm, and 4 mm) and volumes (2%, 4%, and 6% of the engine clearance volume) were selected and manufactured in-house. The experimental investigation of these pre-chamber configurations was carried out in a constant-volume combustion chamber with optical access. The flame development process was captured using a high-speed camera at a rate of 20000 fps, and the images were processed in MATLAB to obtain quantitative data. The combustion characteristics of hydrogen-air mixtures with the PCSI system improved when compared to the conventional SI system; however, the improvement was more significant for ultra-lean mixtures. Early start of combustion and shorter combustion duration were observed for PCSI – D2 and PCSI – D3 configurations, respectively and improved combustion and flame jet characteristics were also noted for these configurations. With the increase in pre-chamber volume, ignition energy associated with the flame jet increases, which reduces the combustion duration and the ignition lag.

Influence of nozzle geometry on wall static pressure coefficient of the submerged turbulent jet impinging on a smooth flat surface

The experimental work is carried out to study the influence of nozzle geometry on the flow characteristics of the submerged turbulent jet impinging on a smooth flat surface. Three nozzle geometry configurations, viz. parabolic, conical and exponential, are considered. Depending upon the nozzle exit diameter, the Reynolds number of 12,000–23,500 and jet-to-plate distance of 0.5–6 is considered. At a higher jet-to-plate distance (z/d = 6), a secondary peak was observed at a radial distance around r/d = 0.4 from the stagnation point. It is due to the transition of fluid flow from laminar to turbulent on the impingement surface. At all Re and z/d, parabolic nozzle geometry resulted in maximum value as compared with other nozzle geometry configurations. This may be attributed to higher pressure losses in the conical nozzle and exponential nozzle than the parabola nozzle because of streamlined flow and this information can be used for local heat transfer phenomena for optimum conditions.