Estimation of heat transfer in oscillating annular flow using artifical neural networks

In this study, the prediction of heat transfer from a surface having constant heat flux subjected to oscillating annular flow is investigated using artificial neural networks (ANNs). An experimental study is carried out to estimate the heat transfer characteristics as a function of some input parameters, namely frequency, amplitude, heat flux and filling heights. In the experiments, a piston cylinder mechanism is used to generate an oscillating flow in a liquid column at certain frequency and amplitude. The cycle-averaged values are considered in the calculation of heat transfer using the control volume approach. An experimentally evaluated data set is prepared to be processed with the use of neural networks. Back propagation algorithm, the most common learning method for ANNs, is used for training and testing the network. Results of the experiments and the ANN are in close agreements with errors less than 5%. The study showed that the ANNs could be used effectively for modeling oscillating flow heat transfer in a vertical annular duct.     

A level-set method for steady-state and transient natural convection problems

This paper introduces a topology optimization method for 2D and 3D, steady-state and transient heat transfer problems that are dominated by natural convection in the fluid phase and diffusion in the solid phase. The geometry of the fluid-solid interface is described by an explicit level set method which allows for both shape and topological changes in the optimization process. The heat transfer in the fluid is modeled by an advection-diffusion equation. The fluid velocity is described by the incompressible Navier-Stokes equations augmented by a Boussinesq approximation of the buoyancy forces. The temperature field in the solid is predicted by a linear diffusion model. The governing equations in both the fluid and solid phases are discretized in space by a generalized formulation of the extended finite element method which preserves the crisp geometry definition of the level set method. The interface conditions at the fluid-solid boundary are enforced by Nitsche’s method. The proposed method is studied for problems optimizing the geometry of cooling devices. The numerical results demonstrate the applicability of the proposed method for a wide spectrum of problems. As the flow may exhibit dynamic instabilities, transient phenomena need to be considered when optimizing the geometry. However, the computational burden increases significantly when the time evolution of the flow fields needs to be resolved.     

CFD assisted modeling for control system design: A case study

This paper presents a novel modeling approach of coupling transient computational fluid dynamics (CFD) simulation with system identification for control system involving fluid flow and heat transfer. In order to illuminate the feasibility of this method, a fluid flow and heat transfer related process, i.e. a three dimension (3-D) spatio-temporal air temperature distribution and input (inlet air temperature) dependent process in the desert climate chamber, is considered. The distributed parameter models of the chamber temperature are identified using transient CFD simulation results and are then validated against the results obtained from the CFD simulations with high RT² (more than 0.97) and negative Young’s information criterion (YIC, less than ?11.8). The PI controllers embedded in CFD simulation are then developed based on the models. The performance of the closed-loop systems is also evaluated within the full-scale CFD model. The results show that CFD-based system identification is feasible to model fluid flow and heat transfer related processes.     

A novel immersed boundary procedure for flow and heat simulations with moving boundary

This article describes a novel immersed boundary procedure for computing the flow and heat transfer problems with moving and complex boundary. Although the immersed boundary techniques have been successfully implemented to these flow and heat simulations, a frequently encountered drawback of this method is the relatively low accuracy proximate to the boundary due to the spreading of forcing function or the interpolation scheme. In this study, we propose a moving-grid process under the arbitrary Lagrangian-Eulerian framework to reduce the numerical diffusion near the immersed boundary. The incompressible Navier-Stokes equations are discretized spatially using unstructured finite element method, and advanced temporally by an operator-splitting scheme. The methodology is validated by the simulations of flow induced by an oscillating cylinder in a free stream. The capability of the proposed method is further demonstrated by good predictions of flow passing the rotating fan in a channel and also flow driven by two independent rotating fans in a circular cavity.     

Modelling the dynamics of the tilt-casting process and the effect of the mould design on the casting quality

All titanium alloys are highly reactive in the molten condition and so are usually melted in a water-cooled copper crucible to avoid contamination using processes such as Induction Skull Melting (ISM). These provide only limited superheat which, coupled with the surface turbulence inherent in most conventional mould filling processes, results in entrainment defects such as bubbles in the castings. To overcome these problems, a novel tilt-casting process has been developed in which the mould is attached directly to the ISM crucible holding the melt and the two are then rotated together to achieve a tranquil transfer of the metal into the mould. From the modelling point of view, this process involves complex three-phase flow, heat transfer and solidification. In this paper, the development of a numerical model of the tilt-casting process is presented featuring several novel algorithm developments introduced into a general CFD package (PHYSICA) to model the complex dynamic interaction of the liquid metal and melting atmosphere. These developments relate to the front tracking and heat transfer representations and to a casting-specific adaptation of the turbulence model to account for an advancing solid front. Calculations have been performed for a 0.4 m long turbine blade cast in a titanium aluminide alloy using different mould designs. It is shown that the feeder/basin configuration has a crucial influence on the casting quality. The computational results are validated against actual castings and are used to support an experimental programme. Although fluid flow and heat transfer are inseparable in a casting, the emphasis in this paper will be on the fluid dynamics of mould filling and its influence on cast quality rather than heat transfer and solidification which has been reported elsewhere.     

基于热平衡和结构强度的发动机 分析平台开发及其应用

建立发动机缸体和缸盖的动力学、燃烧和流体有限元模型,进行发动机热平衡、冷却散热和结构强度研究。创建发动机正向设计和分析方法,革新产品开发流程,自主开发热平衡计算平台。建立发动机缸内和水套传热、流体、温度场、强度的计算模型库,设计水套优化方法和流场评价标准,正向计算发动机热平衡和水套散热。通过2个应用案例,证明该平台在发动机热平衡计算和结构分析与评估中的作用。该平台可为发动机热平衡、冷却散热和结构强度的正向设计提供基础。     

非均匀分布颗粒群中的曳力分布

本文采用格子Boltzmann方法(LBM)在图形处理器(GPU)上计算了由静止圆柱阵列组成的团聚物周期单元内的不可压缩流体流动,流固交界面处采用直接反弹以实现无滑移边界,每个圆柱上的曳力通过统计动量交换直接求得。根据LBM求得的流体速度,对于团聚物中的单圆柱按能量最小多尺度(EMMS)模型计算平均曳力系数,并考察了将聚团近似为均匀悬浮的临界条件。对颗粒雷诺数Re_p在0～10之间的80种固相份额的模拟结果表明,密相空隙率可以表征这种临界条件。当固相份额恒定时,该临界空隙率随着Re_p的增加而降低;当Re_p恒定时,该临界空隙率随着固相份额的增加而降低。     

极端温度环境中舰船弹库传热技术研究

根据《GJB1060.2-1991舰船环境条件要求-气候环境》标准,建立了舰船弹库在高温日照环境与极端低温环境下的传热模型。将太阳辐射和环境温度转化为综合温度,对弹库内部流场进行了流固耦合的二维计算仿真,分析了弹库内部温度在高温日照环境中的连续性变化以及在低温环境中的分布情况。仿真结果表明弹库具有良好的隔热保温性能,所做研究可以为舰船弹库的设计和使用提供决策参考依据和技术支撑。     

基于INTESIM-GISCI的流固耦合 仿真软件技术及应用

为突破传统商业软件流固耦合分析仅局限于内部预先集成的流体和结构求解器的约束,使流固耦合分析更具开放性和可拓展性,以耦合驱动程序INTESIM GISCI为框架体系,在开源流体求解器SU2的源代码上加入时间同步点和相关函数功能形成INTESIM-SU2,使INTESIM-SU2可以与原有的结构求解器INTESIM-Structure通过耦合界面传递数据的方式进行耦合分析,从而实现基于耦合驱动程序INTESIM-GISCI的流固耦合仿真软件开发。将多个流固耦合分析案例与其他商业软件进行对比,证明基于INTESIM-GISCI的流固耦合仿真软件可广泛应用于实际工程问题的仿真分析。     

Multi-objective optimization of the heat transmission and fluid forces around a rounded cornered square cylinder

The unsteady fluid stream and warmth transmission nearby a square cylinder with sharp and rounded cornered edges are numerically examined, and then the roundness of the corner is predicted and optimized for the minimum fluid forces and maximum heat transmission rate. The roundness of the cylinder corner is changing 0.5D (circle) to 0.71D (square); D is the depth of the cylinder. The fluid flow and the heat transmission features around the sharp and curved cornered square cylinder are evaluated with the streamline, isotherm patterns, pressure coefficient, drag and lift coefficients, local Nusselt number (Nu_local) and average Nusselt number (Nu_avg) at different Re and for several roundness values. These characteristics are predicted by the gene expression programming, and then the multi-objective genetic algorithm is utilized for the optimization. A number of combinations of values of corners have been found in the form of Pareto-optimal solution to compromise the minimum fluid forces with maximum heat transfer rate.

     

Compression ratio estimation based on cylinder pressure data

Four methods for compression ratio estimation based on cylinder pressure traces are developed and evaluated for both simulated and experimental cycles. The first three methods rely upon a model of polytropic compression for the cylinder pressure. It is shown that they give a good estimate of the compression ratio at low compression ratios, although the estimates are biased. A method based on a variable projection algorithm with a logarithmic norm of the cylinder pressure yields the smallest confidence intervals and shortest computational time for these three methods. This method is recommended when computational time is an important issue. The polytropic pressure model lacks information about heat transfer and therefore the estimation bias increases with the compression ratio. The fourth method includes heat transfer, crevice effects, and a commonly used heat release model for firing cycles. This method is able to estimate the compression ratio more accurately in terms of bias and variance. The method is more computationally demanding and is therefore recommended when estimation accuracy is the most important property.     

Transient flow and heat transfer mechanism for Williamson-nanomaterials caused by a stretching cylinder with variable thermal conductivity

The utilization of nanometre-sized solid particles in working fluids has been seriously recommended due to their enhanced thermal characteristics. This suspension of solid particles in base fluids can significantly enhance the physical properties, such as, viscosity and thermal conductivity. They are widely used in several engineering processes, like, heat exchangers, cooling of electronic equipment, etc. In this exploration, we attempt to deliver a numerical study to simulate the nanofluids flow past a circular cylinder with convective heat transfer in the framework of Buongiorno’s model. A non-Newtonian Williamson rheological model is used to describe the behavior of nanofluid with variable properties (i.e., temperature dependent thermal conductivity). The leading flow equations for nanofluid transport are mathematical modelled with the assistance of Boussinesq approximation. Numerical simulation for the system of leading non-linear differential equations has been performed by employing versatile, extensively validated, Runge–Kutta Fehlberg scheme with Cash–Karp coefficients. Impacts of active physical parameters on fluid velocity, temperature and nanoparticle concentration is studied and displayed graphically. It is worth to mention that the temperature of non-Newtonian nanofluids is significantly enhanced by higher variable thermal conductivity parameter. One major outcome of this study is that the nanoparticle concentration is raised considerably by an increasing values of thermophoresis parameter.

     

Optimal combustion control with application to engine design and development

The need to reduce development time whilst simultaneously improving engine performance has motivated this application of optimal control to product development processes for engines and powertrains. The optimisation of the fuel consumption is formulated as a constrained Optimal Control Problem (OCP) and solved using pseudospectral methods, giving the optimum heat release and injection profiles in the presence of cylinder pressure rate and cylinder pressure constraints. The technique is applied to an engine design problem and used to reduce fuel consumption by optimising compression ratio within a cylinder pressure limit, also providing new insights into the combustion processes.     

基于虚拟温度法的间歇过程换热器网络综合

提出了基于时间段模型(TSM)综合间歇过程换热器网络的方法,用虚拟温度法代替传统的单一最小传热温差,将各流股的温差贡献值作为决策变量,年度总费用最小作为目标函数建立数学模型.应用遗传膜拟退火算法对上述数学模型进行求解,分别获得每个时间间隔内的子换热器网络结构,并进一步对总换热器网络做结构优化,使其既满足流股的换热要求,又满足年费用最小.方法应用于实例计算,结果比基于最小传热温差获得的换热器网络年度总费用节省6.0%,换热器减少5台,说明这种方法既节省费用,又简化了网络结构.     

Levelset based fluid topology optimization using the extended finite element method

This study focuses on finding the optimal layout of fluidic devices subjected to incompressible flow at low Reynolds numbers. The proposed approach uses a levelset method to describe the fluid-solid interface geometry. The flow field is modeled by the incompressible Navier?CStokes equations and discretized by the extended finite element method (XFEM). The no-slip condition along the fluid-solid interface is enforced via a stabilized Lagrange multiplier method. Unlike the commonly used porosity approach, the XFEM approach does not rely on a material interpolation scheme, which allows for more flexibility in formulating the design problems. Further, it mitigates shortcomings of the porosity approach, including spurious pressure diffusion through solid material, strong dependency of the accuracy of the boundary enforcement with respect to the model parameters which may affect the optimization results, and poor boundary resolution. Numerical studies verify that the proposed method is able to recover optimization results obtained with the porosity approach. Further, it is demonstrated that the XFEM approach yields physical results for problems that cannot be solved with the porosity approach.     

Effect of temperature gradient orientation on the characteristics of mixed convection flow in a lid-driven square cavity

The effect of temperature gradient orientation on the fluid flow and heat transfer in a lid-driven differentially heated square cavity is investigated numerically. The transport equations are solved using the high-order compact scheme. Four cases are considered depending on the direction of temperature gradient imposed. The differentially heated top and bottom walls result in gravitationally stable and unstable temperature gradients. While the differentially heated left and right side walls lead to assisting and opposing buoyancy effects. The governing parameters are Pr = 0.7 and Ri = 0.1, 1, and 10. It is found that both Richardson number and direction of temperature gradient affect the flow patterns, heat transport processes, and heat transfer rates in the cavity. Computed average Nusselt number indicates that the heat transfer rate increases with decreasing Ri regardless the orientation of temperature gradient imposed. And the assisting buoyancy flows have best performance on heat transport over the other three cases.     

Visual simulation of heat shimmering and mirage

We provide a physically-based framework for simulating the natural phenomena related to heat interaction between objects and the surrounding air. We introduce a heat transfer model between the heat source objects and the ambient flow environment, which includes conduction, convection, and radiation. The heat distribution of the objects is represented by a novel temperature texture. We simulate the thermal flow dynamics that models the air flow interacting with the heat by a hybrid thermal lattice Boltzmann model (HTLBM). The computational approach couples a multiple-relaxation-time LBM (MRTLBM) with a finite difference discretization of a standard advection-diffusion equation for temperature. In heat shimmering and mirage, the changes in the index of refraction of the surrounding air are attributed to temperature variation. A nonlinear ray tracing method is used for rendering. Interactive performance is achieved by accelerating the computation of both the MRTLBM and the heat transfer, as well as the rendering on contemporary graphics hardware (GPU)     

Pragmatism in semi-steady modular finite-grid simulation methodology for aerospace composites manufacturing

In this paper, practical aspects of employing the finite element/nodal control volume (FE/NCV) approach for modelling of prepreg moulding, resin transfer moulding and pultrusion of fibre reinforced polymer composites are discussed. Various NCV based formulations for simulating resin flow through fibrous media, resin cure, heat transfer in fabrication assemblies, changes in material properties with temperature and cure are explained. The development of a process-adaptive, modular, semi-steady simulation procedure that combines the benefits of a commercially available general-purpose FE package and user-defined computer programs for NCV grid is presented. The process is easily implementable for one-, two- or three-dimensional domains without re-meshing. Implications of ignoring the effects of the heat of exothermic cure reaction, the artificial loss of resin mass during the resin flow, and the die temperature on material properties are highlighted using example problems.