CFD PREDICTION OF THE TRAJECTORY OF HOT EXHAUST FROM THE FUNNEL OF A NAVAL SHIP IN THE PRESENCE OF SHIP SUPERSTRUCTURE

The superstructure of a modern naval ship is fitted with multitude of sensors for electronic surveillance, weapon discharge, navigation, communication and varieties of deck handling equipment. Locating these electronic equipment/sensors and its integration on board is of paramount importance to achieve optimal operational performance of the naval vessel. Among the many problems in locating these sensors (like stability, EMC EMI etc.,), the presence of entrapped hot gases from the ship exhaust affects the functioning of these electronics. Hence the prediction of temperature profile and trajectories of the ship exhaust plume from the funnel around the superstructure during the design stage is a mandatory requirement for positioning the sensors on superstructure. This trajectory prediction is not amenable to theoretical analysis or empirical calculation procedures in the modern warship superstructure. Experimental and CFD studies conducted on ship superstructure are the only reliable tools that are available to estimate temperature field as well as to study the exhaust smoke superstructure interaction on ships. This paper presents the CFD simulation of the published results for two cases, namely hot jet in a cross flow and hot exhaust with a cross flow on a generic frigate. Simulations have been made using k-ɛ turbulence model with different values of turbulent Schmidt number. It has been observed that temperature field is predicted with reasonable accuracy with turbulent Schmidt number of 0.2.

Estimation of the turbulent Schmidt number in a model gas turbine combustor

This article presents the estimation of turbulent Schmidt number in a model gas turbine combustor. Different gases are used as the model fuel while maintaining the mass flow rate. The simplest closure models for Reynolds stress and turbulent flux are considered. The anisotropy of turbulent viscosity is demonstrated.

Numerical Simulation of the Exit Temperature Pattern of an Aircraft Engine Using a Temperature-Dependent Turbulent Schmidt Number

This paper presents a numerical simulation for predicting the combustor exit temperature pattern of an aircraft engine, developed using the commercial fluid simulation software Ansys Fluent, which assumes a shape probability density function for the instantaneous chemistry in the conserved scalar combustion model and the standard k-ε model for turbulence. We found the compliance of the radial and circumferential non-uniformities of the exit temperature with the experimental data to be insufficient. To achieve much more accurate result, the mixing intensity was enhanced with respect to the initial calculation due to using the reduced value of the turbulent Schmidt number Sc. Numerical simulation was performed for values of the turbulent Schmidt number from Sc = 0.85 (default) up to Sc = 0.2, with results confirming the reduction of radial and circumferential non-uniformities of exit temperature. However, correlation between radial and circumferential non-uniformities is not admissible for these cases. Therefore, we propose to use a temperature-dependent formulation of the turbulent Schmidt number Sc, accounting for the increase in Sc number with increasing gas temperature. A user defined function (UDF) was used to implement the Sc number temperature dependence in Ansys Fluent. The numerical results for the proposed Schmidt number Sc temperature dependence were found to be in acceptable agreement with the experimental data both for radial and circumferential non-uniformities of the exit temperature pattern.

Расчетная оценка влияния неравномерности распыла топлива на поле температур газа на выходе из камеры сгорания ГТД

This paper presents the results of numerical simulation of a gas flow with the combustion of atomized liquid fuel (the equilibrium combustion model pdf was used along with the model of a partially mixed mixture) in an annular combustion chamber of a gas turbine engine. Numerical modeling was carried out in the ANSYS Fluent computational complex. The purpose of the calculations was to assess the influence of the unevenness of the fuel spray specified in the design documentation and the coking of the parts of the front-line device on the radial and circumferential unevenness of the gas temperature field at the exit from the combustion chamber. The simulation used the previously verified turbulence model k-e with the functional dependence of the turbulent Schmidt number Sc on the gas temperature, which was implemented in the ANSYS Fluent computational complex using the user function (UDF). Since the fuel injector and the swirler represent a rather complex spraying scheme, which does not allow calculating the amount of fuel entering through the holes in the swirler cap, an installation was made and tests were carried out to determine the amount of the fuel-air mixture distributed over the holes in the swirler cap. The experimental values of the distribution of the air-fuel mixture through the holes in the swirler cap were further used to perform numerical simulation of combustion in the combustion chamber. Numerical modeling was carried out with sector non-uniformity equal to 0 %, 50 % (the maximum allowable according to the design documentation), and during coking of the swirler cap holes. As a result of the calculations, it was found that the sector irregularity of 50 % has an insignificant effect concerning the sector irregularity of 0 % on the radial irregularity of the gas temperature field at the exit from the combustion chamber, while the circumferential irregularity at the exit from the combustion chamber increased by 1.6 %. to the sectorial unevenness 0 %. When coking the holes of the swirler cap, the value of the radial diagram at the outlet from the combustion chamber increases by 1.2%, and the value of the circumferential irregularity increases by 4%.

Effects of the Turbulent Schmidt Number on the Mass Exchange of a Vegetated Lateral Cavity

<p>Computational Fluid Dynamics (CFD) has been established as a relevant technique to investigate the qualitative and quantitative characteristics of complex environmental flows, such as transient storage zones. In numerical studies involving mass transport of solutes and sediment (e.g., mean retention time and mass exchange rate), one fundamental variable is the turbulent Schmidt number (Sct) which defines the ratio of momentum diffusivity to mass diffusivity in turbulent flows, and thus affects the concentration of solute within the solution impacting on the estimation of mass related variables. This is particularly important for transient storage zones, such as lateral cavities and groyne fields, as they are known for their role in nutrient retention and release, and sediment entrapment. This numerical study aims to examine the influence of the turbulent Schmidt number in the mean retention time and mass exchange rate between a channel and a vegetated/non-vegetated lateral cavity.</p><p> </p><p>The cavity was <em>L</em> = 0.25m long (x-axis), <em>W</em> = 0.15m wide (y-axis) and had a depth of <em>H</em> = 0.10m (z-axis). The aspect ratio between the width and the length resulted in 0.6 which corresponded to a single circulation system (Sukhodolov et al., 2002). The flow had a bulk velocity of <em>U</em> = 0.101 m/s that corresponds to a Reynolds number of 9000. The vegetation drag was represented by an anisotropic porous media calculated with the Darcy-Forchheimer model (Yamasaki et al., 2019), the vegetation density was constant at <em>a</em> = 0.1332%. Large Eddy Simulation (LES) was applied to define the flow field in that domain, using the Wall Adapting Local Eddy-viscosity (WALE) to account subgrid effects. A passive scalar was injected inside the lateral cavity to investigate its transport and diffusion in a range of Sct from 0.1 to 2.0. The numerical results of the flow field were validated using literature experimental data considering 3 different meshes to achieve mesh independence (Xiang et al., 2019).</p><p> </p><p>The effect of Sct variation was, then, analysed in both vegetated and non-vegetated scenarios, for a total of 40 different simulations. The volumetric average scalar concentration in the cavity was fitted into a first-order decay model <em>(C</em> = <em>C<sub>0</sub>.e<sup>-t/T<sub>D</sub></sup></em>), where <em>C<sub>0</sub> = 1</em> is the initial concentration, <em>t</em>  (s) is time and <em>T<sub>D</sub></em>  is the mean residence time. The mass exchange rate was defined as <em>k</em> = <em>W/(T<sub>D</sub>.U)</em> . Preliminary results showed in the vegetated scenarios a limited effect of Sct on the mass exchange rate, which varied from 1% if the Sct value was doubled.</p><p><strong>References</strong></p><p>Sukhodolov, A., Uijttewaal, W. S. J. and Engelhardt, C.: On the correspondence between morphological and hydrodynamical patterns of groyne fields, Earth Surf. Process. Landforms, 27(3), 289–305, doi:10.1002/esp.319, 2002.</p><p>Xiang, K., Yang, Z., Huai, W. and Ding, R.: Large eddy simulation of turbulent flow structure in a rectangular embayment zone with different population densities of vegetation, Environ. Sci. Pollut. Res., 26(14), 14583–14597, doi:10.1007/s11356-019-04709-x, 2019.</p><p>Yamasaki, T. N., de Lima, P. H. S., Silva, D. F., Preza, C. G. de A., Janzen, J. G. and Nepf, H. M.: From patch to channel scale: The evolution of emergent vegetation in a channel, Adv. Water Resour., doi:10.1016/j.advwatres.2019.05.009, 2019.</p>

Numerical Simulation of a GH2/LOx Single Injector Combustor and the Effect of the Turbulent Schmidt Number

A large-eddy simulation (LES) of a gaseous hydrogen/liquid oxygen (GH2/LOX) single-injector rocket combustor is performed in this study. The Redlich–Kwong–Peng–Robinson (RK–PR) equation of state is used to simulate the real-gas effect under high-pressure conditions, and the steady laminar flamelet model (SLFM) is implemented to simulate fast chemistry, such as a H2/O2 reaction. From the numerical simulation, the characteristics of time-averaged flow and flame fields are obtained, and their relationship with the real-gas effect is investigated. It is possible to investigate unsteady flame features and the mixing mechanism of propellants in detail by examining multiple snapshots of the field contour. Another purpose of the study is to investigate the differences in flow and flame structures according to the variation in the turbulent Schmidt number. By comparing the simulation result with the natural OH* emission image and temperature profiles from experimental data, the appropriate range of the turbulent Schmidt number for the simulation is obtained. Furthermore, this paper suggests the usefulness and validity of the current research by quantitatively comparing (i.e., temperature profiles) numerical results with those of existing literature.