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Nowadays, synthetic jets have various applications such as cooling enhancement and active flow control. In the present paper, the capability of two turbulence modelling approaches in predicting thermal performance of an impinging synthetic jet is investigated. These two approaches are scale adaptive simulation (SAS) and detached eddy simulation (DES). Comparisons between numerical data and experimental studies reveal that the ability of DES in predicting the asymmetrical trend of heat transfer profiles is better than SAS in almost all the study cases. Although, near the stagnation zone, the performance of SAS is superior. Results show that the effects of parameters such as frequency, cross-flow velocity and suction duty cycle factor are well predicted by both approaches. An increase of cross-flow velocity from 1.81 m/s to 2.26 m/s results in an improvement of [Formula: see text] near the stagnation point by almost 16.3% and 9.2% using DES and SAS, respectively.

Combination of transient computational fluid dynamics simulations of a gas-fired heat treatment furnace and experimental validation were carried out to investigate the applicability of equilibrium ...

A combination of unsteady 3D CFD simulations and experimental temperature measurements was employed to determine the effect of loading patterns on the temperature distribution within steel forgings inside a gas-fired heat treatment furnace. This was aimed to obtain a more homogenous temperature distribution. Besides, a hybrid methodology using 3D numerical simulations and a high-resolution dilatometer allowed improving residence time of forgings inside the heat treatment furnace. The influence of the loading patterns and skids on temperature distribution and residence time of forgings was examined using thermal analysis four different loading patterns. Comprehensive unsteady thermal analysis of the products heating allowed quantifying the impact of skids usage and their dimensions on the extent of the uniformity of temperature distribution. The results were interpreted in terms of the inter-relationship between the skids usage, their geometry, absorbed radiation, and convective heat fluxes. The analysis showed that temperature non-uniformities of up to 331 K could be produced for non-optimum loading patterns. Using the developed CFD approach, it was possible to reduce the temperature non-uniformity of different sizes of blocks up to 32% via changing the loading pattern inside the furnace. Further, the slab’s residence time was improved by almost 15.5% when employing the proposed hybrid approach. This approach could directly be applied to the optimization of different heat treatment cycles of forged blocks in different grades of steels.

The present paper investigates the turbulent flow and heat transfer of non-Newtonian aqueous solution of Carboxymethyl cellulose (CMC) and CuO nanoparticles in a plain tube and also tube with twisted tape inserts. The aqueous solution of CMC and CuO/CMC nanofluid show a shear-thinning (pseudo-plastic) rheological behavior, resulting in a higher viscosity than that of water. The consistency index and the power law index are evaluated based on available experimental data. The single phase approach with temperature dependent thermo-physical properties is applied to simulate the nanofluid flow and heat transfer. Simulation results are presented at different nanoparticle concentrations and twisted tape ratios. Only an axial flow is identified in the plain tube whereas both axial and swirl flows are detected in the tube with twisted tape inserts. The turbulence kinetic energy in the tube with twisted tapes is significantly higher than that in the plain one, which is useful for non-Newtonian fluid with higher viscosity. Also, the temperature fields in the tube with twisted tapes are disturbed relative to those in the plain one, due to stronger turbulence intensity and better fluid mixing. Higher amounts of nanoparticles concentration and lower twist ratios, giving maximum values of total efficiency, display the advantage of using non-Newtonian nanofluid in the tube with twisted tape inserts rather than non-Newtonian base fluid in the plain one.

The present paper’s main goal is to investigate the turbulence structures and combustion characteristics in a model wall jet can combustor (WJCC) employing the large eddy simulation (LES) approach. The laminar flamelet combustion and discrete ordinates radiation models are applied in an Eulerian–Lagrangian approach to simulate a reactive spray flow. The results illustrate that LES together with an appropriate mesh and a suitable time step could properly capture the coherent vortical structures, including vortex tube, streamwise and hairpin vortices throughout the model WJCC. Also, the energy cascade from the largest turbulence length scale (integral length scale) at lower frequency of the spectrum to the smallest one along with the recirculation zones is revealed suitably. At the beginning of WJCC, immediately after the swirler, a region of dense coherent structures is formed that can influence the sharp fluctuations of the droplet. In the primary and intermediate zones the hairpin vortices and in the dilutions zone the streamwise vortices are observed more. A significant temperature reduction and a maximum scalar dissipation rate are detected in the head of hairpins. Results also indicate that the strain rate and flow temperature have an inverse relationship. The greatest strain rate is visible at the center of the collision of the primary jets and the main stream, where there is minimum temperature. The largest values of temperature are detected in the intermediate zone under the influence of the largest reverse flow.

The objective of the present article is to investigate the effects of thermal radiation on turbulent mixed convection in a vertical square duct under variable thermophysical properties and the non-...

A comprehensive study of turbulent combustion is carried out to analyze the relationship between entropy generation and soot formation in turbulent vaporized kerosene/air jet diffusion flames. Deal...

In the present article, the flow field and passive gaseous pollutant dispersion in a naturally cross-ventilated isolated single-zone model building have been investigated. The large eddy simulation (LES) approach has been applied together with three different sub-grid scale (SGS) models, namely, wall-adapting local eddy-viscosity (WALE), dynamic Smagorinsky-Lilly model (DSLM), and standard Smagorinsky-Lilly model (SSLM). The flow and passive scalar concentration fields have been compared with available experimental data. It is demonstrated that the three SGS models predict similar flow field. Also, it can be observed that the mean concentration field results obtained from the WALE sub-grid scale (SGS) model are in better agreement with the experimental data than those of DSLM and SSLM by about 8% and 5%, respectively. Moreover, the CPU time required for the computations by the WALE and SSLM models was almost 20% less than that of DSLM, making WALE a more suitable SGS model than the other two models for the prediction of flow and concentration fields in an isolated building. Furthermore, contributions of convective flux and turbulent diffusion flux to the pollutant transportation have been studied. It has been shown that although the convective flux is the main mechanism, the two fluxes have a significant influence on pollutant transportation and distribution.

Analysis of the turbulent forced convective heat transfer of CuO/water nanofluid has been conducted employing an artificial neural network. A backpropagation network with two hidden layers has been used to investigate and optimize the effects of the Reynolds number, volume fraction and nanoparticle diameter on heat transfer, pressure drop and entropy generation. In order to train the network, the Levenberg–Marquardt algorithm has been applied. The results of a total of 168 sample models, considering the extended range of input data, have been prepared as the training data for the network. The precision of the network based on the mean squared error for a set of random experimental data has been approximately 0.05. The obtained results of the artificial neural network are presented in an extended range of Re, $$\varphi$$ and particle diameter. Results indicate that heat transfer enhancement is achieved by increasing Re and volume fraction. While augmenting Re reduces the friction factor, it is increased at higher volume fractions. The optimum conditions concerning Nusselt number, friction factor and entropy generation have been investigated. For instance, at low volume fractions, the ratio $$Nu/f^{1/3} S^{2}$$ has the highest value in the range $$5 \times 10^{4} < Re < 6 \times 10^{4}$$ , which is a proper range of performance for the nanofluid.

Simulation and analysis of thermal interactions during heat treatment is of great importance for accurate prediction of temperature evolution of work pieces and consequently controlling the final microstructure and mechanical properties of products. In the present study, a three-dimensional CFD model was employed to predict the heating process of large size forged ingots inside an industrial gas-fired heat treatment furnace. One-ninth section of a loaded furnace, including details such as fixing bars and high-momentum cup burners, was employed as the computational domain. The simulations were conducted using the ANSYS-FLUENT commercial CFD package. The k-ε, P-1 and Probability Density Function (PDF) in the non-premix combustion, as low computational cost numerical approaches were employed to simulate the turbulent fluid flow, thermal radiation, combustion and conjugate heat transfer inside the furnace. Temperature measurement at different locations of the forged ingot surfaces were used to validate the transient numerical simulations. Good agreement was obtained between the predictions of the CFD model and the experimental measurements, demonstrating the reliability of the proposed approach and application of the model for process optimization purposes. Detailed analysis of conjugate heat transfer together with the turbulent combustion showed that the temperature evolution of the product was significantly dependant on the furnace geometry and the severity of turbulent flow structures in the furnace.

A comprehensive investigation applying the large eddy simulation approach to turbulent forced convection of CuO/water nanofluid flowing through a horizontal channel is carried out. Dealing with the...

The main purpose of this article is to investigate the effects of pressure and temperature of incoming air into an evaporating chamber on fuel spray evaporation and fuel droplets characteristics. Before that, the influences of secondary break-up and coupling between droplets and gas phase on the present spray modeling are studied. An Eulerian-Lagrangian approach and two-way coupling model are implemented for modeling spray and atomization of liquid fuel in air. The SSTk - ω turbulence model is applied to estimate eddy viscosity, whilst the discrete random walk model is employed to trace the droplets in a turbulent flow. With increasing inlet air temperature from 373 to 573 K, the lifetime and penetration depth of droplets are reduced by about 70% and 46%, respectively. The influence of incoming air pressure on droplets lifetime is not remarkable. The penetration of droplets is reduced by almost 61% while augmenting the air pressure from 1.0 to 10.0 atm.

In this paper, the large eddy simulation (LES) approach is employed to investigate the role of different thermal stratification conditions (stable, neutral and unstable) in the air flow and gaseous...

The present paper investigates the turbulent forced convection of TiO2/water nanofluid through a ribbed flat-plate solar collector numerically. A three-dimensional simulation of solid flat-plate with flow through the plain and ribbed duct has been performed. The scale-adaptive-simulation approach has been employed to simulate the flow turbulence. The velocity and temperature profiles, Nusselt number and the efficiency of solar flat-plate solar collector have been studied by using plain and ribbed ducts at different Reynolds number and nanoparticles volume fraction. Results indicate that wake circulation region in the back of the rib is intensified at higher Reynolds number leading to an enhancement in the convective heat transfer. Moreover, the efficiency of flat-plate solar collector increases with the nanoparticles volume fraction whilst an enhancement in the efficiency of the ribbed duct is approximately 10% higher than that of the plain duct. This enhancement varies for different nanofluids such that the CuO/water nanofluid provides a higher thermal efficiency than that of TiO2/water.

In order to improve the cooling process in impingement synthetic jets, it is necessary to evaluate the influence of dimensionless parameters and the geometry of the flow field and heat transfer. In this paper, the effects of geometry (confined and unconfined impingement synthetic jets), and jet-to-surface spacings, Reynolds number and dimensionless stroke length on a three-dimensional unsteady impingement synthetic jet are studied. For this purpose, two types of turbulence models, namely the v 2 − f and S S T / k − ω , have been employed. The simulation results have been indicated that the v 2 − f model comparing to the S S T / k − ω model has a close agreement with the available experimental data. The results show that the flow field and the corresponding heat transfer distribution of the impingement synthetic jet are affected by geometry such that an unconfined impingement synthetic jet is more efficient in a cooling process relative to the confined case. Also, increasing jet-to-surface spacing affects the vortex structure and consequently the heat transfer. The stagnation heat transfer rate reaches to the maximum value at an optimum impingement distance as a result of the appropriate ventilation and the coherence vortex structures. The stagnation heat transfer rate experiences several extrema as a result of the increasing stroke length and under the higher stroke length, the impingement synthetic jet acts similar to the impingement continuous jet.

In the present study, turbulent mixed convection of CuO-water nanofluid is investigated in a vertical duct. In order to simulate the nanofluid flow, the fluid phase is considered as continuous whil...

The present paper focuses on the turbulent mixed convection of nanofluids through a vertical square duct. The prediction accuracy of scale-adaptive simulation (SAS) approach is investigated versus RANS-based models (k − e and k − ω), in terms of Nusselt number and friction factor. A thermal-dependent model is considered to determine the effective thermal conductivity and effective dynamic viscosity of nanofluids. The present numerical simulations are performed for CuO–water and SiO2–water nanofluids and compared with various experimental data. Results indicate that the SAS approach can predict the unsteady flow and heat transfer of nanofluids more accurately than the k − e and k − ω models. Moreover, it is found that the turbulent velocity fluctuations enhance in streamwise, spanwise and wall-normal directions with an increasing nanoparticle volume fraction, whilst this increment is higher in streamwise direction. Also, in the near-wall region the effect of the presence of nanoparticles on the turbulent velocity fluctuations is more considerable, which increases the turbulence content of the flow field.

The present study investigates the effects of fluid thermo-physical property variations on fully developed turbulent mixed convection flow in vertical and horizontal parallel plate channels where w...

The objective of present paper is to assess the influence of different chemical mechanisms on nonpremixed combustion of kerosene liquid fuel in a gas turbine model combustor. Simulation of two-phase reacting flow is performed employing realizable k – e turbulence, laminar flamelet combustion, and discrete ordinates radiation models in a structured finite volume grid. An Eulerian–Lagrangian approach is applied to model spray of liquid fuel. Distributions of mean axial velocity, temperature, scalar dissipation rate, mixture fraction, mass fraction, and rate of formation of carbon dioxide, water vapor, and nitrogen monoxide are compared for three different cases (three different chemical reaction mechanisms). Results depict that minimum deviations concerning the mean axial velocity and mean temperature are observed for case A, which consists of 17 species and 26 reaction steps. The maximum scalar dissipation rate is shown for case B, comprising 21 species and 30 reactions steps due to a higher mixture fracti...

The present paper evaluates the relative performance of scale-adaptive simulation (SAS) in modelling unsteady concentration and flow fields around a model building relative to other transient simul...

In the present paper, the analysis of concentration and flow fields around a model building was performed using two different approaches in turbulence modeling. In the first approach, the non-linear model of Ehrhard and Moussiopoulos was employed as one of the best cubic non-linear eddy viscosity models, and large eddy simulation was utilized in the second approach. The obtained results suggest that although the non-linear model has the ability to predict the anisotropic normal components of Reynolds stress tensor, due to time-averaged nature of its governing equations, it is incapable of estimating the correct values of Reynolds stress components and turbulent characteristics in the wake region of the model building. So the predicted turbulence kinetic energy values by the non-linear model are 45% smaller than those of large eddy simulation approach in the wake region behind the model building. Also different predictions of the wake region structure by the non-linear model and large eddy simulation approach revealed that elongation of iso-surface for $$\left\langle K \right\rangle$$ = 1.5 in non-linear model is 56% more than that of large eddy simulation approach. The large eddy simulation approach shows much consistent behavior to the physics governing the flow compared to the non-linear model. Also good agreement observed between the results obtained through this approach and the experimental data. However, the disadvantage of large eddy simulation approach is the high computational costs.

The purpose of present study is to numerically investigate the radiation effects on turbulent mixed convection flow between two differentially heated vertical parallel plates. Two flow situations known as aiding and opposing flow are considered. Frictional Reynolds number and Grashof number are assumed to be 150 and 1.6 × 106, respectively. Both hydrodynamically and thermally developing and fully developed regions in the channel are investigated. Three Reynolds-averaged Navier–Stokes-based low Reynolds turbulence models are evaluated and the model with better overall performance is applied to the simulations. The radiative transfer equation for the gray and participating fluid is solved using the discrete-ordinates method, adopting its eighth-order quadrature scheme. The effects of two radiative parameters, namely, wall emissivity and optical thickness, on the flow and thermal fields, Nusselt number, and friction factor are addressed. Present results indicate that the presence of thermal radiation...

The present work provides the computations of unsteady 3D synthetic jet ejected into a quiescent ambient. The [Formula: see text] turbulence model is employed for numerical simulations of flow field and the problem is considered under incompressible and axisymmetric assumptions. The pressure-implicit with splitting of operators algorithm is used for coupling of continuity and momentum equations. In order to accurately simulate the synthetic jet actuator, the dynamic mesh method is employed to model the flow field. In different simulations, pressure inlet, pressure outlet and wall boundary conditions at the orifice outlet of the synthetic jet are investigated. Changes in the boundary conditions at the orifice outlet affect the flow field such that mean velocity magnitude is higher for unconfined synthetic jets than confined ones. Moreover, form of vortex rings is dissimilar for confined and unconfined jets. Also, the actuator is modelled with two types of inlet boundary conditions, namely, moving piston and moving diaphragm boundaries. Results show that they have no significant difference and can be used interchangeably.

The present paper investigates the performance of various inflow turbulence generation techniques (ITGT) for large eddy simulation (LES) of flow and dispersion around a model building in a turbulent atmospheric boundary layer. Four different ITGT comprising 1 – no fluctuations, 2 – spectral method, 3 – vortex method and 4 – internal mapping, based on two basic methodologies (i.e. precursor and synthetic turbulence methods), are employed. These techniques are evaluated by considering their prediction accuracy, computational costs, complexity of implementation, inflow information required to operate and impacts on the flow downstream of the inlet, particularly in the wake region of the model building. Results indicate that the accuracy of LES predictions is greatly reliant on ITGT. It is shown that ITGT not only have significant effects on flow field vortical structures, but also influence frequency contents of velocity fluctuations, recirculation regions and plume shapes in the wake region.

The present paper focuses on a three-dimensional unsteady turbulent synthetic jet to assess the accuracy of a compressible simulation and some important parameters including the simulations of the actuator, cavity height and Reynolds number. The two-equationSST/k− ω turbulence model is used to predict the flow behaviour. Results show that the compressible simulation case is more accurate than the incompressible one and the dynamic mesh exhibits more reliable results than the mass flow inlet boundary in the compressible simulation. The compressible case displays a delay in the phase of instantaneous velocity for all three Reynolds numbers. Also, the maximum of mean velocity is less than the incompressible case. Moreover, an increase in the Reynolds number leads to an amplification of the peak of mean velocity magnitude. Finally, results demonstrate that a reduction in the cavity height regarding the compressible simulation case causes a reduction in the phase delay and rise in peak of instantaneous velocity magnitude.

In the present article, the potential of embedded large eddy simulation (ELES) approach to reliably predict pollutant dispersion around a model building in atmospheric boundary layer is assessed. The performance of ELES in comparison with large eddy simulation (LES) is evaluated in several ways. These include a number of qualitative and quantitative comparisons of time-averaged and instantaneous results with wind tunnel measurements supplemented by statistical data analyses using scatter plots and standard evaluation metrics. Results obtained by both LES and ELES approaches show very good agreement with the experiment. However, addition of turbulence to mean flow at Reynolds averaged Navier–Stokes (RANS)–LES interface in ELES approach not only increases the turbulence intensity, it also results in larger values of turbulent kinetic energy (TKE) as well as a shorter reattachment length in the wake region. Accordingly, higher levels of TKE predicted by ELES increase the local intensity of concentration leading to shorter plume shapes as compared with LES. In general, ELES shows better agreement with experiment on the surfaces of model building and also in the downstream wake region. In terms of computational costs, the CPU time required to obtain statistical values in ELES is about 49 % lower than that of LES and the number of iterations per time step is also reduced by 55 % as compared with LES.

Natural ventilation, a useful mechanism to moderate the indoor temperature and to disperse pollutants, is a complex engineering problem to analyze due to a large number of influential factors such as wind direction, size, and location of openings, etc. The present paper investigates the effect of different shapes of openings, with a constant wall porosity, namely, horizontally long, squared and vertically long, on cross-ventilation in a generic isolated building. Flow and passive pollutant concentration fields are the performance indicators. The large eddy simulation (LES) approach together with the wall-adapting local eddy-viscosity (WALE) sub-grid scale (SGS) model is employed for the simulations. Validation results, based on available wind-tunnel measurements, of time-averaged velocity and pollutant concentration for the reference case are reported. Results display that the performance of cross-ventilation in reducing the pollutant concentration enhances as the height to width ratio of the openings increases and the building with horizontally long openings is the most contaminated case. The ventilation performance in the case of vertically long openings is shown to be the most effective one. Furthermore, present findings show that the participation of the turbulent diffusion flux in the passive pollutant transportation becomes smaller as the flow makes progress toward the downstream.

In this paper, the effects of the sub-grid scale (SGS) turbulent Schmidt number, Sc SGS, on the large eddy simulation of dispersion on and around an isolated cubical model building with a flush vent located on its roof are examined. Constant and dynamic Sc SGS approaches for SGS turbulent mass flux modeling are employed. Simulation results are compared with the available wind tunnel measurements. Furthermore, the influence of the grid resolution on the accuracy of results predicted by the dynamic Sc SGS approach is investigated. Detailed statistical analysis of Sc SGS demonstrates that the dynamically computed Sc SGS at different locations varies by a factor of almost 5 and a considerable deviation of Sc SGS from its common values of 0.5 and 0.7 occurs. Particularly, in the vicinity of the building where the concentration gradients are noticeable, Sc SGS has a larger variation. Also, the probability of occurrence of 0.2 < Sc SGS

Prediction accuracy of various non-linear eddy viscosity turbulence models for simulating flow and pollutant dispersion on and around an isolated cubical model building with a rooftop vent within the neutral turbulent boundary layer was investigated. For this purpose, three types of quadratic along with three cubic non-linear models were employed and simulation results were compared with the available wind tunnel measurements and linear revised k-ɛ models. They were different from the preceding simulations which have only concentrated on the wind flow field around buildings. Detailed analysis of dispersion mechanisms based on convective and turbulent diffusion mass fluxes indicated that concentration distributions predicted by non-linear models at the sidewall improved significantly relative to the traditional standard k-ɛ and linear revised k-ɛ models which was due to larger lateral turbulent diffusion. Moreover, thorough analysis of these fluxes underlined the prominent capability of non-linear models in capturing the anisotropy of turbulence and verified the importance of recirculation regions in the pollutant dispersion around a model building. Among the various non-linear models under study, cubic models of Craft et al. and Ehrhard and Moussiopoulos provided the best performance as compared with the other numerical and experimental data.

Comprehensive unsteady analysis of large size forged blocks heating characteristics in a gas-fired heat treatment furnace was carried out employing experimentally measured temperatures and computational fluid dynamics (CFD) simulations. Heat and fluid flow interactions, consisting of turbulence, radiation and combustion, were simultaneously considered using k-ε, DO and EDM models in a three dimensional CFD model of the furnace, respectively. Applicability of the S2S radiation model was also evaluated to quantify the effect of participating medium and radiation view factor in the radiation heat transfer. Temperature measurements at several locations of an instrumented large size forged block and the furnace chamber were performed. A maximum deviation of about 7% was obtained between the model predictions and the experimental measurements. Results showed that despite the unloaded furnace had uniform temperature distribution, after loading, product surfaces experienced different heating rates, resulting in temperature differences up to 200 K. Findings were correlated with furnace geometry, vortical structures and flow circulations around the workpiece. Besides, S2S model demonstrating reliable results highlighted the importance of radiation view factor optimization in this application. The study could directly be employed for optimization of the heat treatment process of large size steel components. Keywords: Heat treatment, CFD simulation, Gas-fired furnace, Temperature measurement, Heating uniformity, Radiation modeling

In the present study, the prediction accuracy of a dynamic one-equation sub-grid scale model for the large eddy simulation of dispersion around an isolated cubic building is investigated. For this purpose, the localized dynamic \(k_\mathrm{SGS} \)-equation model (LDKM) is employed and the results are compared with the available experimental data and two other classic sub-grid scale models, namely, standard Smagorinsky–Lilly model (SSLM) and dynamic Smagorinsky–Lilly model (DSLM). It is shown that the three SGS models give results in good agreement with experiment. However, near the ground level of the leeward wall, dimensionless time-averaged concentration, \(\langle K\rangle \), profile is not quite similar to the experimental data. It is also demonstrated that the LDKM predicts the values of \(\langle K\rangle \) on the roof, leeward and side walls more acceptably than the SSLM and DSLM. Whereas, the streamwise elongation of time-averaged structures of the plume shape is more over-estimated with the LDKM than with the other two SGS models. In terms of numerical difficulty, the LDKM is found to be stable and computationally reasonable. In addition, it does not suffer from a flow dependent constant such as the Smagorinsky coefficient employed in the SSLM model.

In the present paper, the influence of grid resolution on prediction accuracy of large eddy simulation (LES) of dispersion around an isolated cubic building was investigated. Several grid resolution assessment techniques in LES, namely, two-point correlations, ratio of SGS viscosity to molecular viscosity and ratio of SGS shear stress to resolved shear stress were considered. It was found that two-point correlations could be regarded as a useful method for evaluation of grid resolution. However, it was highly time consuming and required extra post-processing calculation. Also, it was shown that ratios of SGS viscosity to molecular viscosity and SGS shear stress to resolved shear stress decreased by improving grid resolution and they did not change significantly by further increasing the grid resolution. Thus, both these ratios were concluded to be an applicable technique for the evaluation of grid resolution in LES.

A plain zero net mass flux (ZNMF) jet injected in a quiescent medium is presently investigated numerically employing the unsteady Reynolds averaged Navier Stokes simulation approach. The flow features encompassing centerline mean velocity evolution, self-similar mean velocity distribution, jet momentum flux and stagnation point location are studied at different jet Strouhal and Reynolds numbers. The present investigation shows that the far field behavior of a plain ZNMF jet somewhat resembles the steady plain turbulent jets. Accordingly, the centerline mean velocity varies on the basis of a power law decaying profile and the cross stream mean velocity distribution illustrates an approximately self-similarity condition. However, it is demonstrated that the present ZNMF jet momentum flux is not constant with the streamwise coordinate contrary to a steady turbulent jet. Also, the stagnation point location is shown to reach its maximum at around t/T = 0.8 and the maximum location strongly depends on the jet S...

The main purpose of the present work is to investigate numerically the effects of number and location of stabilizer jets on the combustion characteristics and NOx emission in a jet-stabilized combustor (JSC). A Finite Volume staggered grid approach is employed to solve the governing equations. The eddy dissipation-finite rate model is adopted for the heat release simulation and the Realizable k − ɛ turbulence model is taken on for the flow predictions. An Eulerian–Lagrangian formulation is used for the two-phase (gas-droplet) flow. The Discrete Ordinates method, adopting its S4 approximation is applied for thermal radiation modeling of the gas phase. It is demonstrated that an increase in axial distance of stabilizer jets from fuel injector results in NOx emission to decrease significantly and conversely it results in thermal power of combustor to enhance slightly. Also, an increase in number of jet holes (with invariable entrance air velocity) causes both the thermal power and NOx emission to enhance. NOx formation is shown to be more sensitive to location of stabilizer jet holes rather than its number. As the distance between stabilizer jets and fuel injector increases from 40 mm to 60 mm and then 80 mm, uniformity of temperature profile is improved which could lead to better conditions at the combustor’s downstream section. This situation is valid for smaller number of stabilizer jets. An increase of stabilizer jets number from 4 to 6 and then 8 leads to an enhanced non-uniformity of temperature distribution towards the downstream.

The present article encompasses an effort on the prediction of flow and heat transfer characteristics in the turbulent axisymmetric impinging jet. This is achieved by applying the realizability constraint in the normal-velocity relaxation (v 2 − f) model and algebraic turbulent heat flux models to flow and thermal fields, respectively. The realizable v 2 − f model is capable of improving the predicted velocity and Reynolds stress and consequently the local Nusselt number as compared with the available experimental data. Applying the higher order algebraic turbulent heat flux models, namely, GGDH and HOGGDH results in a larger wall jet heat diffusion. This causes an improvement in the predicted local Nusselt number through its reduction in both the stagnation and wall jet regions. For the local Nusselt number prediction, the realizable v 2 − f model in combination with HOGGDH model is shown to be in reasonably good agreement with the available experimental data. This is also regarded as an overall progress...

In all industries which are related to heat, suitable thermal ranges are defined for each device to operate well. Consideration of these limits requires a thermal control unit beside the main system. The Satellite Thermal Control Unit (STCU) exploits from different methods and facilities individually or mixed. The space radiating fin which is combined with a heat pipe can be used to transfer the excess heat from the satellite to outer free space. The finite volume method is employed to simulate numerically the temperature distribution in a space radiating fin and evaluate thermal fin efficiency. Final results are achieved for two different materials (Aluminum and Beryllium) and compared to each other. The present results are compared with the other analytical methods and good agreement is shown.

The present paper focuses on the analysis of unsteady flow and heat transfer regarding an axisymmetric impinging synthetic jet on a constant heat flux disc. Synthetic jet is a zero net mass flux jet that provides an unsteady flow without any external source of fluid. Present results are validated against the available experimental data showing that the SST/k − ω turbulence model is more accurate and reliable than the standard and low-Re k − e models for predicting heat transfer from an impinging synthetic jet. It is found that the time-averaged Nusselt number enhances as the nozzle-to-plate distance is increased. As the oscillation frequency in the range of 16–400 Hz is increased, the heat transfer is enhanced. It is shown that the instantaneous Nu distribution along the wall is influenced mainly by the interaction of produced vortex ring and wall boundary layer. Also, the fluctuation level of Nu decreases as the frequency is raised.

The objective of the present work is to investigate the modeling of a two-phase reactive flow concerning a diesel oil/air flame in order to predict the turbulent flow behavior and temperature distribution in a three dimensional jet-stabilized model combustion chamber. A Finite Volume staggered grid approach is adopted to solve the governing equations. The second-order upwind scheme is applied for the space derivatives of the advection terms in all transport equations. An Eulerian–Lagrangian formulation is used for the two-phase (gas–droplet) flow. The presumed PDF is taken on to model the heat release and the Realizable k–e turbulence model is applied for the flow predictions. The thermal radiation model for the gas-phase is based on the Discrete Ordinates Method, adopting its S4 approximation. Comparisons of present numerical predictions with available experimental data and also with another numerical solution employing different combustion and turbulence models reveal that the Realizable k–e model predicts jet flow behavior more accurately than the standard k–e model. Also, the presumed PDF model predicts the temperature distribution better than the eddy dissipation model, especially in the near wall region. Negligence of thermal radiation mode results in a failure to predict the concentration of NO species.