Turbulent Slot Jet Research Articles

Effects of hydrogen blending and exhaust gas recirculation on NO[formula omitted] emissions in laminar and turbulent [formula omitted] flames at 25 bar

In this work, the effect of Exhaust Gas Recirculation (EGR) on NOx emissions in a CH4/H2/air combustion at 25 bar, at an equivalence ratio Φ = 0.7, is analyzed in laminar and turbulent partially premixed flames. Numerical simulations of twenty premixed and partially premixed counterflow flames with H2 ranging from 0 to 100%, with and without EGR, are carried out. Analysis of NO formation mechanisms shows that the thermal path is the main responsible for the NOx production in each flame, with a contribution of nearly 80%. In laminar flames an increase of H2 leads to an increase in NOx emissions. The addition of the exhaust gas decreases the flame temperature and therefore NOx: each laminar flame shows a NOx reduction of about 60% with the presence of exhaust gas. Four turbulent slot jet flames with a CH4/H2/Air/EGR premixed central core and Air/EGR as coflow are studied in a two-dimensional framework using the Reynolds Averaged Navier–Stokes (RANS) approach and the Large Eddy Simulation (LES) methodology, to take into account some flame dynamics, despite the 2D context. Accurate molecular transport properties are considered and, a reduced specifically designed chemical mechanism for methane/hydrogen-air combustion at Φ=0.7, consisting of 48 transported species and 465 elementary reactions is adopted. The four turbulent flames were simulated with 0 and 50% hydrogen concentration, with and without EGR. The presence of hydrogen reduces CO2 emissions, but at the same time increases NO concentration, the thermal path being the main NO formation mechanism. The use of exhaust gas recirculation leads to NO reduction as in laminar flames. The results obtained in this work show that at high pressure, the hydrogen enrichment of natural gas in the EGR mode leads to lower NOx as well as CO2 emissions.

Analysis of melting of phase change material inserted a block via impinging turbulent slot jet

PurposeThe purpose of this study is to do a numerical analysis of the jet to a body filled with phase change material (PCM). The melting of the PCM filled body was investigated by the hot jet flow. Four different values of the Reynolds number were taken, ranging from 5 × 103 = Re = 12.5 103. Water, Al2O3 1%, Al2O3 2% and hybrid nanofluid (HNF; Al2O3–Ag mixture) were used as fluid types and the effects of fluid type on melting were investigated. At 60 °C, the jet stream was impinged on the PCM filled body at different Reynolds numbers.Design/methodology/approachTwo-dimensional analysis of melting of PCM inserted A block via impinging turbulent slot jet is numerically studied. Governing equations for turbulent flow are solved by using the finite element method via analysis and system fluent R2020.FindingsThe obtained results showed that the best melting occurred when the Reynolds number increased and the HNF was used. However, the impacts of using alumina-water nanofluid were slight. At Re = 12,500, phase completion time was reduced by about 13.77% when HNF was used while this was only 3.93% with water + alumina nanofluid as compared to using only water at Re = 5,000. In future studies, HNF concentrations will change the type of nanoenhanced PCMs. In addition, the geometry and jet parameters of the PCM-filled cube can be changed.Originality/valueEffects of impinging jet onto PCM filled block and control of melting via impinging hot jet of PCM. Thus, novelty of the work is to control of melting in a block by impinging hot jet and nanoparticles.

A direct numerical simulation analysis of localised forced ignition in turbulent slot jets of CH4/CO2 blends

The early stages of flame evolution following successful localised forced ignition of different CH[Formula: see text]/CO[Formula: see text] blends in a slot jet configuration have been analysed using three-dimensional direct numerical simulations. The simulations have been conducted for three different concentration levels of CO[Formula: see text] in the fuel blend composed of CH[Formula: see text] and CO[Formula: see text] (ranging from 0% to 20% by volume). The effects of CO[Formula: see text] concentration have been analysed based on five different energy deposition scenarios which include situations where the mean mixture composition at the ignitor varies, but not its location in space, whereas other cases represent the scenarios where the mean mixture composition within the energy deposition region remains constant, but its spatial location changes with CO[Formula: see text] concentration. The most favourable region for successful flame development following thermal runaway, from the mixture composition standpoint (i.e. the highest flammability factor), has been found to be displaced close to the nozzle with an increase in CO[Formula: see text] concentration. The flame development following thermal runaway exhibits initial growth of hot gas kernel followed by downstream advection and eventual flame propagation along with radial expansion with a possibility of flame stabilisation irrespective of the level of CO[Formula: see text] concentration. The triple flame propagation has been found to play a key role in the upstream flame propagation and eventual stabilisation. The orientation of the local flame normal plays a key role in the flame stabilisation. The lift off height has been found to increase with increasing CO[Formula: see text] concentration which also adversely affect flame stabilisation for high levels of CO[Formula: see text] concentration.

Experimental and LES study of unconfined jet impingement on a smooth flat heated plate with slots of different widths

ABSTRACT The present work focuses on the experimental and large-eddy simulation (LES) investigation of fluid flow and heat transfer due to the impingement of an unconfined turbulent slot jet on a smooth flat plate. Three LES sub-grid scale models are validated with the experimental observations for first time in terms effect of slot widths. A detailed parametric study is conducted considering nozzle to plate spacing ratio from 4 to 12, non-dimensional slot width from 0.015 to 0.035, and Reynolds number range from 4000 to 12000. The results show an appreciable change in the stagnation point and along the wall jet Nusselt numbers with the change in Reynolds number, nozzle-to-plate spacing and non-dimensional slot width. No significant effect of nozzle to plate spacing is observed along the wall jet Nusselt number beyond the streamwise location at 0.2. The local Nusselt number increases with an increase in Reynolds number while it decreases with an increase in nondimensional slot width. Comparison of various LES sub-grid models with RANS (k-ω SST) turbulence model is performed. The results show that turbulent kinetic energy plays a major role in enhancing the heat transfer rate. Dissipation of the turbulent kinetic energy increases with an increase in nozzle to plate spacing and non-dimensional slot width. Further, a correlation is proposed for the stagnation point and wall jet region Nusselt numbers in terms of effect of slots width, Reynolds number and non-dimensional nozzle to plate spacing.

Characterization of laminar and turbulent supercritical carbon dioxide slot jet impingement heat transfer

Supercritical carbon dioxide (sCO2) has recently been proposed as a promising alternative to conventional fluids for thermal management because of its unique thermophysical properties near the critical point. Jet impingement is also recognized as one of the most effective configurations for high intensity heat transfer. Therefore, leveraging the favorable thermophysical properties of sCO2 in microscale jet impingement may lead to high performance thermal management solutions. However, the effects of thermophysical property variations in the pseudo-critical temperature range on the flow and heat transfer behavior in such configurations is not well understood. The present investigation seeks to address this need through computational simulations of laminar and turbulent slot sCO2 jet impingement. Large eddy simulations (LES) are validated and employed for turbulent cases. The studied range of conditions span reduced pressures of Pr=1.03−1.10, Reynolds numbers Re=225−11,000, dimensionless jet lengths H/W=2−4, jet inlet temperatures Tin=294−330K, and impingement plate temperatures Tplate=270−370K. The turbulent simulations reveal varying spatial distributions of heat transfer coefficient with different jet and plate temperatures, which can be explained in terms of the temperature-dependent properties of sCO2. Heat transfer deterioration (HTD) is observed for both laminar and turbulent flows. HTD is found to be most significant in the stagnation zone, and its relative magnitude decreases downstream more sharply for turbulent flows than laminar. Heat transfer enhancement (HTE) is observed when both the jet inlet and impingement plate temperatures are at opposite ends of the pseudo-critical temperature range. For cooling applications, HTD and HTE effects can be explained in terms of opposing temperature-dependent variations in boundary layer thermal conductivity and overall thermal boundary layer thickness with Prandtl number. Considering the dependence of thermophysical properties on Pr, a thermal management system control strategy is proposed in which Pr is adjusted depending on Tplate to achieve optimal performance over varying operating conditions.

Computational analysis of convective heat transfer properties of turbulent slot jet impingement

PurposeConvective heat transfer features of a turbulent slot jet impingement are comprehensively studied using two different computational approaches, namely, URANS (unsteady Reynolds-averaged Navier–Stokes equations) and SAS (scale-adaptive simulation). Turbulent slot jet impingement heat transfer is used where a considerable heat transfer enhancement is required, and computationally, it is a quite challenging flow configuration.Design/methodology/approachCustomized OpenFOAM 4.1, an open-access computational fluid dynamics (CFD) code, is used for SAS (SST-SAS k-ω) and URANS (standard k-ε and SST k-ω) computations. A low-Re version of the standard k-ε model is used, and other models are formulated for good wall-refined calculations. Three turbulence models are formulated in OpenFOAM 4.1 with second-order accurate discretization schemes.FindingsIt is observed that the profiles of the streamwise turbulence are under-predicted at all the streamwise locations by SST k-ω and SST SAS k-ω models, but follow similar trends as in the reported results. The standard k-ε model shows improvements in the predictions of the streamwise turbulence and mean streamwise velocity profiles in the zone of outer wall jet. Computed profiles of Nusselt number by SST k-ω and SST-SAS k-ω models are nearly identical and match well with the reported experimental results. However, the standard k-ε model does not provide a reasonable profile or quantification of the local Nusselt number.Originality/valueHybrid turbulence model is suitable for efficient CFD computations for the complex flow problems. This paper deals with a detailed comparison of the SAS model with URANS and LES for the first time in the literature. A thorough assessment of the computations is performed against the results reported using experimental and large eddy simulations techniques followed by a detailed discussion on flow physics. The present results are beneficial for scientists working with hybrid turbulence models and in industries working with high-efficiency cooling/heating system computations.

Turbulent flame speed and reaction layer thickening in premixed jet flames at constant Karlovitz and increasing Reynolds numbers

A series of Direct Numerical Simulations (DNS) of lean methane/air flames was conducted to investigate the enhancement of the turbulent flame speed and modifications to the reaction layer structure associated with the systematic increase of the integral scale of turbulence l while the Karlovitz number and the Kolmogorov scale are kept constant. Four turbulent slot jet flames are simulated at increasing Reynolds number and up to Re≈22,000, defined with the bulk velocity, slot width, and the reactants’ properties. The turbulent flame speed ST is evaluated locally at selected streamwise locations and it is observed to increase both in the streamwise direction for each flame and across flames for increasing Reynolds number, in line with a corresponding increase of the turbulent integral scale. In particular, the turbulent flame speed ST increases exponentially with the integral scale for l up to about 6 laminar flame thicknesses, while the scaling becomes a power-law for larger values of l. These trends cannot be ascribed completely to the increase in the flame surface, since the turbulent flame speed looses its proportionality to the flame area as the integral scale increases; in particular, it is found that the ratio of turbulent flame speed to area attains a power-law scaling l0.2. This is caused by an overall broadening of the reaction layer for increasing integral scale, which is not associated with a corresponding decrease of the reaction rate, causing a net enhancement of the overall burning rate. This observation is significant since it suggests that a continuous increase in the size of the largest scales of turbulence might be responsible for progressively stronger modifications of the flame’s inner layers even if the smallest scales, i.e., the Karlovitz number, are kept constant.

Performance analysis of different turbulence models in impinging jet cooling

The characteristics of heat transfer from a hot wall surface for the oblique impingement of a free turbulent slot jet have been investigated numerically. Different turbulent models — the [Formula: see text]-[Formula: see text], [Formula: see text]-[Formula: see text], SST [Formula: see text]-[Formula: see text], cubic [Formula: see text]-[Formula: see text] and quadratic [Formula: see text]-[Formula: see text] models — are used for the prediction of heat transfer and their results were compared with experimental results reported in the literature. The comparison shows that the [Formula: see text]-[Formula: see text], quadratic [Formula: see text]-[Formula: see text] and SST [Formula: see text]-[Formula: see text] models give more unsatisfactory results for the investigated configuration, while the cubic [Formula: see text]-[Formula: see text] model is capable of predicting the local Nusselt number in wall-jet region only. The [Formula: see text]-[Formula: see text] model exhibits the best agreement with the experimental results in both stagnation and wall-jet regions. Further, the [Formula: see text]-[Formula: see text] model is applied to analyze the obliquely impinging jet heat transfer problem. The parametric effects of the jet inclination ([Formula: see text], [Formula: see text] and [Formula: see text]), jet-to-surface distance ([Formula: see text], 6 and 8), Reynolds number ([Formula: see text], 15[Formula: see text]000 and 20[Formula: see text]000), and turbulent intensity ([Formula: see text], [Formula: see text] and [Formula: see text]) have been presented. The heat transfer on the upward direction is seen to decrease, while that on the downward direction it rises for the increasing angle. It is to be noted that as the value of [Formula: see text] decreases, the point of maximum Nusselt number ([Formula: see text]) displaces toward the upward direction from the geometric center point as well as its value reduces. The shifting of the [Formula: see text] is found to be independent of Re and [Formula: see text] within the range considered for the study.

Influence of moving plate velocity on conjugate heat transfer due to the impingement of an inclined slot jet

In this paper, a dimensionless numerical study of the flow-field and heat transfer characteristics of an incompressible turbulent slot jet impinging obliquely over a moving surface of finite thickness is presented. Simulations were performed using [Formula: see text] eddy viscosity turbulence model. The temperature field was solved simultaneously in the solid and the fluid domain. For a fixed impingement distance and a fixed Reynolds number, the impingement angle ([Formula: see text]) and plate velocity ([Formula: see text]) were varied in the range of 30–75∘ and 0–0.3, respectively. In the results, the length of the potential core depends on the jet inclination, which increases with increase in jet angle. The jet angle and plate velocity have more influence on the uphill side compared to the downhill side. The location of stagnation displaces toward the uphill side as the inclination angle decreases, and the drifting of stagnation point is noted with the variation in plate velocity. The average skin-friction coefficient increases with increase in [Formula: see text] and [Formula: see text], and the influence of [Formula: see text] on the skin-friction coefficient is reduced as [Formula: see text] increases. The maximum Nusselt number ([Formula: see text]) increases with increase in [Formula: see text], and the drifting of [Formula: see text] is observed with increase in plate velocity. It is found that the average Nusselt number increases quickly with increase in plate velocity for lower angles of impingement. The distribution of local heat flux follows the same trend as the local Nusselt number.

Flow and thermal characteristics of jet impingement on a flat plate for small nozzle to plate spacing using LES

This paper presents a study of flow and thermal characteristics of jet impingement heat transfer by large eddy simulation (LES) using the wall adapting local eddy (WALE) viscosity sub-grid scale (SGS) model. OpenFOAM 4.1, a finite-volume based customized open source computational fluid dynamics (CFD) solver, is used for computations. Turbulent slot jet impingement on a solid flat plate for a small nozzle to plate spacing (H/B = 4, where H denotes the gap between jet and plate and B the slot width) and Reynolds number of 20000 is considered. The capability of the WALE SGS model is first evaluated by comparing the results of flow and heat transfer features including turbulence profiles with the reported experimental results and good agreements are observed. A secondary peak in Nusselt number (Nu) profile on the impingement plate is observed in accordance with the reported results. In order to gain a good understanding of flow and heat transfer characteristics, mean and r.m.s. values of velocity and temperature, Nusselt number (Nu), turbulent structures and iso-surfaces of various flow properties were analyzed in detail. Large coherent structures, flow acceleration and an augmentation in turbulence were correlated with the existence of a secondary peak in Nu profile. A detailed discussion on flow and heat transfer characteristics is presented in the vicinity of stagnation, impingement plate and wall jet regions.

Computational investigation of slot jet impinging on a heated flat plate using low-Reynolds number modeling

The present work reports the computational investigation of turbulent slot jet impinging on a heated plate subjected to isothermal and isoflux boundary conditions. The eddy viscosity based 2-equation low-Reynolds number k − ε model of Yang and Shih has been considered. Low-Reynolds number (LRN) modeling employ near-wall integration which solves the entire boundary layer using very find grid near the wall to handle the sharp gradient of variables prevailing in these regions. The Reynolds number of jet at the inlet is 9900 and the non-dimensional distance between the top and bottom plate i.e. H/w is 7.5. The variation of centerline axial velocity, variation of local maximum axial velocity, profile of non-dimensional wall shear stress along impingement and confinement wall, distribution of local Nusselt number along impingement wall and confinement wall, and distribution of Reynolds shear stress in the domain are discussed.

Evaluation of a developed SST k-ω turbulence model for the prediction of turbulent slot jet impingement heat transfer

In this paper, a turbulence model based on OpenFOAM has been developed for the jet impingement heat transfer, which is based on the standard SST k-ω model and considers the effects of cross-diffusion term and the Kato-Launder model. The effects of the modifications have been studied for different nozzle-plate spacing of 4 and 9.2 in terms of pressure distributions, mean velocity, skin friction and the local Nusselt number distributions. The results have been compared with both the experimental data and the numerical results in the literatures. Good agreement is obtained in the studied cases and the developed model overcomes the false secondary Nusselt number peak in high nozzle-plate spacing for slot jets which is predicted by the standard SST k-ω model. The results show that the modifications improve the model’s ability to predict the heat transfer for jet impingement by reinforcing the model’s sensitivity to the pressure gradient. By way of comparative studies, it shows that the SST k-ω with transition model and the standard SST k-ω model are not sensitive to the pressure gradient. Meanwhile, the cases of nozzle-plate spacing of 2 and 6 are also investigated. This investigation indicates that the pressure gradient plays an important role for turbulent slot impinging jet. And it also reveals that the effect of cross-diffusion term should not be ignored in the boundary layer.

Effect of inclination of twin impinging turbulent jets on flow and heat transfer characteristics

This paper presents analyses of complex flows and heat transfer induced by twin oblique turbulent slot-jets of different directions (divergent, convergent or parallel) impinging a heated wall. A comparison of the heat transfer characteristics between perpendicular and three cases of twin oblique jets (parallel, convergent and divergent). The twin slot jets are located on a confining adiabatic wall at a distance of 8 slot jet width. Convective heat is investigated numerically examining the effect of Reynolds number (Re) and jet inclination angle (α). This problem is relevant to a wide range of practical applications including nuclear engineering devices, manufacturing, material processing, electronic cooling, drying paper or textile, tempering of glass, etc. All computations are performed using two dimensional large eddy simulations (LES) approach with Smagorinsky sub-grid scale (SGS) models. For all directions and inclinations of the jets, the location of the stagnation points is changed and hence, the location and magnitude of the maximum Nusselt number on the heated wall vary. When Reynolds number increases, Nusselt number is improved for all types of inclination. The averaged Nusselt number shows that the perpendicular impingement gives better heat transfer than that of the oblique jets. The poor heat transfer is obtained for the parallel oblique jets. For the same angle, divergent jets give smallest heat transfer than the convergent jets.

Effect of Slot Jet Temperature on Impingement Heat Transfer Over a Heated Circular Cylinder

In this paper, heat transfer and effectiveness of a turbulent slot jet impinging over a heated circular cylinder have been investigated numerically by varying the ratio of jet temperature to the ambient temperature, Θj = Tj/Tamp, from 0.7 to 1.2. In all cases, the ambient temperature (Tamb) is assumed to be constant (300 K). The Reynolds number defined based on the average nozzle exit velocity, the diameter of the cylindrical target (D), and properties at the nozzle exit temperature, ReD=ρVD/μ is varied from 6000 to 20,000. The ratio of cylinder diameter to the slot width, D/S = 5.5, 8.5, and 17 are considered and the nondimensional distance from the nozzle exit to the cylinder, H/S is varied in the range of 2 ≤ H/S ≤ 12. The v′2¯−f turbulence model was used for numerical simulations. Numerical results reveal that the local Nusselt number is found to be higher at the stagnation point in the case of cold jet impingement at Θj = 0.7. The local heat transfer at the rear side of the cylinder is 8–18% less as compared to that of Θj = 1.0 for ReD = 6000. The local effectiveness calculated over a circular cylinder strongly depends on H/S and D/S. Based on the parametric study, a correlation has been provided for the local effectiveness at the stagnation point.

OpenFOAM based LES of slot jet impingement heat transfer at low nozzle to plate spacing using four SGS models

The objective of the present investigation is to assess the effectiveness of large eddy simulation (LES) in turbulent slot jet impingement heat transfer at low nozzle to plate spacing. Four different sub-grid stress (SGS) models, namely, Smagorinsky, WALE (wall adapting local eddy-viscosity), k-equation and dynamic k-equation, were considered for Reynolds number of 20,000. Computations were performed using OpenFOAM, an open source finite-volume based CFD code. Time and span-wise averaged mean streamwise velocity and root mean square (r.m.s.) velocity fluctuations in the stagnation and wall jet regions are presented. Nusselt number distributions on the impingement wall are also presented. The computed LES results are compared with the reported experimental data. A secondary peak in the Nusselt number was observed using the four SGS models as in the experimental data. LES of slot jet impingement heat transfer using four SGS models, including WALE, has been investigated for the first time in the present paper. It is observed that the WALE and dynamic k-equation SGS models perform well in complex flow regions of turbulent slot jet impingement heat transfer.

Heat transfer and flow characteristics of turbulent slot jet impingement on plane and ribbed surfaces

A computational study is carried out to assess the suitability of various RANS based turbulence models for slot jet impingement on flat and ribbed surfaces with various values of Reynolds number and jet to plate spacing. The com-puted results are compared with the reported experimental data. It was observed that none of the turbulence models considered predicted the heat transfer data accurately. However, some models predicted the experimental data with good trends, e.g., secondary peak and several spikes in Nusselt number for ribbed surface, with a precise computation of the stagnation point Nusselt number. Further, the effects of slot width, rib pitch and jet to ribbed surface spacing were investigated for jet impingement on a ribbed surface. It was observed that the local Nusselt number increased with slot width and rib to plate spacing. It was also observed that increasing Reynolds number had a positive effect on the local heat transfer. With increasing rib pitch the local Nusselt number increased near the stagnation zone but de-creased downstream. The observed flow pattern was different for jet impingement on a ribbed surface than that on a flat surface.

Experimental investigation and large eddy simulations of turbulent slot jet impingement cooling of a circular cylinder with and without a quadrilateral confinement

In the present study, experimental and numerical investigations have been carried out on a slot jet impinging over a circular cylinder in order to understand fluid flow and heat transfer characteristics. To understand instantaneous and average flow characteristics, large eddy simulations (LES) are carried out. To enhance heat transfer at the rear portion of the cylinder, a quadrilateral shape confinement with openings at the top and the bottom was used around the cylinder. The ratio of the cylinder diameter to the slot width is fixed at D/S = 10.6 and the non-dimensional distance from the nozzle exit to the cylinder, H/S = 4 and 8 are considered. The Reynolds number, defined based on the cylinder diameter and the average velocity at the nozzle exit, ReD = (ρVjD/µ) considered are 12000 and 20000. The present LES results show that the average velocities and the Reynolds stresses compare well with the experimental results available in the literature. Rolled vortices are observed significantly before and after the jet impingement in the case of unconfined flow. In the case of confined flow, the local heat transfer at the bottom potion of cylinder is enhanced by around 23% due to the suppression of large recirculation and the acceleration of flow in the confined passage. The time and the span wise averaged Nusselt number of the cylinder obtained from the present LES agree well with the present experimental results.

On the statistics of flame stretch in turbulent premixed jet flames in the thin reaction zone regime at varying Reynolds number

Direct Numerical Simulations (DNS) are conducted to study the statistics of flame surface stretch in turbulent jet premixed flames. Emphasis is placed on the rates of surface production and destruction and their scaling with the Reynolds number. Four lean methane/air turbulent slot jet flames are simulated at increasing Reynolds number and up to Re ≈ 22 × 103, based on the bulk velocity, slot width, and the reactants’ properties. The Karlovitz number is held approximately constant and the flames fall in the thin reaction zone regime. The simulations feature finite rate chemistry and mixture-average transport. Our data indicate that the area of the flame surface increases up to the streamwise position corresponding to 80% of the average flame length and decreases afterwards as surface destruction overtakes production. It is observed that the tangential rate of strain is responsible for the production of flame surface in the mean and surface destruction is due to the curvature term. In addition, it is found that these two terms are both significantly larger than their difference, i.e., the net surface stretch.The statistics of the tangential strain rate are in good agreement with those for infinitesimal material surfaces in homogeneous isotropic turbulence. Once scaled by the Kolmogorov time scale, the means of both contributions to stretch are largely independent of location and equal across flames with different values of the Reynolds number. Surface destruction is due mostly to propagation into the reactants where the surface is folded into a cylindrical shape with the center of curvature on the side of the reactants. The joint statistics of the displacement speed and curvature of the reactive surface are nuanced, with the most probable occurrence being that of a negative displacement speed of a flat surface, while the surface averaged displacement speed is positive as expected.

Assessment of subgrid scale mixing models used in LES at high pressures

ABSTRACTMolecular mixing models for conditional scalar diffusion (CSD) in the filtered mass density function (FMDF) transport equation used in Large Eddy Simulations are evaluated against direct numerical simulation (DNS) of spatially evolving jets. A database of DNS of turbulent mixing slot jets of and is developed. The formulation includes compressible form of the governing equations, a generalized diffusion model, a real gas equation of state and realistic property models. Simulations are conducted at initial pressures between 1-100 atm and Reynolds numbers of 850, 1300. The CSD term in the FMDF transport equation is calculated from the DNS. An a priori analysis of Interaction by Exchange of Mean, Modified Curl and Mapping Closure models for CSD is conducted. At high pressures, significant deviations are observed between the CSD measured from the DNS and those predicted by the models. The source of the deviations is determined to be the mixing frequency used in the models. The significance of this term and its variation with change in pressure and diffusion models is studied. The primary objective of this work is to assess the applicability of the aforementioned models to flows at large pressures and determine the causes for deviation in prediction.

Modeling and computation of turbulent slot jet impingement heat transfer using RANS method with special emphasis on the developed SST turbulence model

Based on the Reynolds-Averaged Navier-Stokes (RANS) method, this work has developed a combinational turbulence model for the numerical simulation of turbulent slot jet impingement heat transfer. The combinational model is constructed by taking the original Shear Stress Transport (SST) turbulence model as the parent model and coupling with the Kato-Launder model, the intermittency transition model and the crossflow transition model, which has been abbreviated as SST-KIC model. Detailed study has been conducted for the effect of different component models in terms of the turbulent kinetic energy, the local Nusselt number as well as the flow structures including the mean velocity, skin friction and the law of wall. By comparing with both experimental data and available numerical results of other researchers, it has been found that the proposed model possesses good performance in terms of different parameters for both two nozzle-plate spacing of 4 and 9.2. Finally, the effect of Reynolds number on the flow field characteristics was studied and it is noted that the positive gradient of turbulent intensity has similar variation tendency as the positive gradient of the Nusselt number.