Automated maze solving using fluid mechanics based numerical approach

Auxiliary Power Units (APU’s) are gas turbine engines which are located in the tail of most commercial and business aircraft. They are designed to provide electrical and pneumatic power to the aircraft on the ground while the main propulsion engines are turned off. They can also be operated in flight, when there is a desire to reduce the load on the propulsion engines, such as during an engine-out situation. Given an APU’s typical position in the back of an airplane, the intake systems for APU’s can be very complex. They are designed to provide sufficient airflow to both the APU and the cooling system while minimizing the pressure losses and the flow distortion. These systems must perform efficiently during static operation on the ground and during flight at very high altitudes and flight speeds. An APU intake system has been designed for a new commercial aircraft. This intake system was designed using the latest Computational Fluid Dynamics (CFD) techniques. Several iterations were performed between the APU supplier and the aircraft manufacturer since each of their components affects the performance of the other. For example, the aircraft boundary layer impacts APU intake performance and an open APU flap impacts aircraft drag. To validate the effectiveness of the CFD analysis, a full scale intake rig was designed and built to simulate the tailcone of the aircraft on the ground. This rig was very large and very detailed. It included a portion of the tailcone and rudder, plus the entire APU and cooling intake systems. The hardware was manufactured out of fiberglass shells, stereolithogrophy components and machined plastic parts. Three different airflows for the load compressor, engine compressor and cooling system had to be measured and throttled. Fixed instrumentation rakes were located to measure intake induced pressure losses and distortion at the APU plenum and cooling ducts. Rotating pressure and swirl survey rakes were located at the load compressor and engine compressor eyes to measure plenum pressure losses and distortion. Static pressure taps measured the flow pattern along the intake and flap surfaces. The intake rig was designed to be flexible so that the impact of rudder position, intake flap position, APU plenum baffle position and compressor airflow levels could be evaluated. This paper describes in detail the different components of the intake rig and discusses the complexity of conducting a rig test on such a large scale. It also presents the impact of the different component positions on intake performance. These results were compared to CFD predicted values and were used to calibrate our CFD techniques. The effectiveness of using CFD for APU intake design and its limitations are also discussed.

In this paper, multi-objective optimization (MOO) of Al2O3-water nanofluid flow in microchannel heat sinks (MCHS) with triangular ribs is performed using Computational Fluid Dynamics (CFD) techniques and Non-dominated Sorting Genetic Algorithms (NSGA II). At first, nanofluid flow is solved numerically in various MCHS with triangular ribs using CFD techniques. Finally, the CFD data will be used for Pareto based multi-objective optimization of nanofluid flow in MCHS with triangular ribs using NSGA II algorithm. In the MOO process there are seven geometrical and non-geometrical parameters and the conflicting objective functions are to simultaneously maximize the amount of heat transfer and minimize the pressure drop. Five optimum designs are determined and discussed for both nanofluid and base fluid flows. Details of design variables for each of five optimum points are deeply discussed. It is shown that the achieved Pareto solution includes important design information on nanofluid flow in MCHS with triangular ribs.

The droplet drift during aerial spraying process of oilseed rape, which is induced by complex flow field including random lateral wind, is difficult to predict and suppress. In this study, the high-fidelity computational fluid dynamics (CFD) technique is employed to simulate the two-phase flow of droplets in the rotor flow field, and the influence of main operation parameters on spraying effect is investigated numerically. Furthermore, the mechanism of droplet deposition in various operation conditions is discussed according to the analysis of unsteady flow field characteristics. However, the simulation via CFD technique is time-consuming, and it is not suitable for multidisciplinary work and optimization design. To address such issue, a filter white Gaussian noise signal is used to mimic the random lateral wind, and the droplet drift distance is obtained numerically. Based on the input and output dataset of CFD, the recursive algorithm including nonlinear autoregressive exogenous model and surrogate-based recurrence framework and the deep learning method for time-series prediction called long short-term memory neural network are used to build the efficient reduced-order model, respectively. Numerical simulations show that the droplet drift distance can be predicted by measurable lateral wind speed via the reduced-order model approach, which agreed well with the results obtained via the CFD method. In addition, the reduced-order model could decrease computation cost by 6 orders of magnitude with an acceptable accuracy, which indicates that the proposed method could be used for the design of off-line closed-loop controller of a variable spraying system.

Computational fluid dynamics (CFD) techniques have become an important tool for investigating and predicting flow behavior in many industrial and engineering processes. In the last two decades, CFD has been used for the study, design, and improvement of irrigation equipment. Numerical simulations can be used to predict fluid flow, heat transfer, and chemical reactions within complex systems. The objective of this review is to provide an overview of the uses of CFD in irrigation engineering applications. The paper is organized into two main sections: fundamentals of CFD and irrigation engineering applications. The first section presents the main methods used in numerical simulations, basic equations to predict fluid flow parameters, meshing concerns, and convergence criteria. In the second section, we present applications related to friction and local head losses in pipes, liquid and solid-liquid flow simulation in drippers, chemical scaling, filters, sprinklers, direct-acting pressure-regulating valves, and Venturi injectors. The briefly described applications indicated that CFD modeling can be an accurate, quick, and feasible method for the investigation of flow parameters in irrigation pipes, fittings, emitters, and accessories. The CFD simulations can be useful for designing new products as well as for improving and optimizing existing products. Computational fluid dynamics uses in irrigation engineering must be encouraged, particularly for innovation purposes resulting from the cooperation between academia and irrigation companies.

The paper describes a numerical study about topography effects on design wind load by using Computational Fluid Dynamics (CFD) techniques. For this purpose a CFD tool was developed using an object oriented approach and C++ programming language. The CFD procedure consisted of solving the Reynolds time-averaged NavierStokes equations and the standard k-e turbulence model using body-fitted nearly orthogonal grids. A robust grid generator tool suitable for producing orthogonal grids over curved and sloping complex surfaces has also been developed. Subsequently, wind load design parameters such as speed-up ratio values were generated for a wide spectrum of terrain geometries that included escarpments, single and multiple hills, and valleys. Ground roughness and geometry approximation effects have been investigated. For validation of the CFD results as well as highlighting advantages and disadvantages of a particular method, results obtained from a variety of sources were compared: the present CFD study, Boundary Layer Wind Tunnel (BLWT) experiments, field measurements, NBCC (1995) provisions, analytical methods, and previous numerical works available in literature. The present CFD results compare well with BLWT data. Speed-up ratio values are produced for both new and covered cases by the Commentaries of National Building Code of Canada (1995).

Flows around a swimmer's body in a prone glide position are computed with a Computational Fluid Dynamics (CFD) technique in order to understand the effect of a body shape on flow characteristics. A human model which consists of artificial bones, joints and an overlying skin is used to model the body shape in the consistent form via manipulation of the joints. A finite-volume based Navier-Stokes solver is used with unstructured tetra, prism and hexahedral grids for the flow computation to cope with the complicated geometry of a human body. The computed results of the underwater swimming show that the pressure drag is more than six times larger than the frictional drag. Various types of longitudinal vortices, flow separations and reattachments are observed due to the concave and convex geometry of the body. The parameter study for the gliding depth is conducted to evaluate the free-surface effects and the wave making resistance. The deformation of free-surface is computed reasonably well and it is shown that the wave making resistance can be estimated by the CFD technique.

In Thailand, RSS chamber of community-level rubber cooperatives can be classified into two models: old and new model, named after the years of their establishment. Hot gas as a heat supply from Para-rubber (PR) wood (Hevea brasiliensis) combustion is used for removing moisture from the natural rubber (NR) sheets. Smoke and soot particles from PR wood burning has effected to the quality of the NR sheet and the pollution in the workplace area and lead to health problems of the worker. Cascade impactors are equipment for measuring the smoke and soot particles size distribution from PR wood combustion. PAHs compounds from PR wood combustion were found 15 different PAHs components (Tekasakul et al., 2005; Furuuchi et al., 2006). Important methods in decreasing smoke and soot particles from combustion of PR wood for rubber smoking chamber are separation equipment and ventilation designed by computational fluid dynamics (CFD) technique. In this article, the separation method is focused on smoke and soot particle collection to maintain the quality of the NR sheet. This equipment is reviewed both indoor and outdoor, for example, an impaction wall, electrostatic precipitator, stainless-wire, etc. This review indicates that the ESP installing between the furnace and the smoking chamber is suitable to eliminate aerosol particles at the rubber smoking industry. In addition, CFD technique reports is aimed at collecting aerosol particles for decreasing smoke and soot particles emission from rubber smoking chamber is presented.

This paper presents a predictive investigation using Computational Fluid Dynamic (CFD) techniques focusing on the study of contamination that occurs between different products in an oil pipeline under normal operating conditions. The use of CFD techniques yields detailed flow conditions including the velocity fields, phase distribution and interface evolution, which can provide valuable information to the oil industry especially in the distribution of oil products. The Volume of Fluid (VOF) model is used in this project in a pipe with two fluids. Simulation results show the interface evolution between the two fluids and how it is affected by properties such as viscosity ratio and pressure difference. Operational data from the Nigerian National Petroleum Corporation was obtained to validate the results from the simulations.

In this research, a Computational Fluid Dynamics (CFD) technique was used to investigate the effect of choking on the flow and heat transfer characteristics of a typical micro-channel heat sink. Numerical simulations have been carried out using Spalart–Allmaras model. Comparison of the numerical results for the heat transfer rate, mass flow rate and Stanton number with the experimental data were conducted. Relatively good agreement was achieved with maximum relative error 16%, and 8% for heat transfer and mass flow rate, respectively. Also, average relative error 9.2% was obtained for the Stanton number in comparison with the experimental values. Although, the results show that the majority of heat was transferred in the entrance region of the channel, but the heat transfer in micro-channels can also be affected by choking at channel exit. Moreover, the results clearly show that, the location where the flow is choked (at the vicinity of the channel exit) is especially important in determining the heat transfer phenomena. It was found that Spalart–Allmaras model is capable to capture the main features of the choked flow. Also, the effects of choking on the main characteristics of the flow was presented and discussed.

In the petroleum refining industry, furnaces are key equipment because they provide the necessary heat to carry out different processes. These furnaces are designed to use natural gas as fuel, but in most cases they use a mixture of waste gases known as refinery gases (RG), which molar composition varies depending on the process in which they are generated, in most cases with high content of propane, hydrogen, propylene, among others. This is done in most cases to save energy and reduce storage cost. However, this variation in molar composition also produces a change in calorific power that can be as high as 1,200 Btu/ft3, producing alterations in the combustion process, affecting efficiency and increasing pollutant emissions. In this work, the Computational Fluid Dynamics (CFD) technique is used to simulate the combustion process in a representative segment of a typical refinery furnace using RG as fuel with 3 different molar compositions. Comparative CFD 3D simulation cases are performed to study the effect of molar composition variability in the temperature and chemical species profiles inside the furnace. The obtained results show that high contents of gases like propane, propylene or hydrogen increase the calorific power and peak temperature inside the furnace, but temperature profile distribution is less uniform. The chemical species profiles inside the furnace show that there is an increase in CO when using mixture gases with low CH4 content, which indicates that a more detailed study regarding air excess and flow is needed. The results are very important because they can be used as a tool for decision-making regarding the convenience to use or not refinery waste gases as fuels in furnaces and to stablish a starting point for a detailed study about the improvement of furnaces operation and process safety.

The computational fluid dynamics (CFD) model has been used to investigate the two-phase flow phenomena such as high-pressure water jet. High-pressure water jet is a new technology and develops rapidly due to its advantages in recent years. In this research, the effects of different models on the macroscopic parameters of jet propagation characteristics of high pressure water jet have been investigated numerically through the CFD technique. The simulations of the water jet with three kinds of k-ε models (i.e., standard, RNG, and realizable k-ε models) have been compared under the same conditions. It may be concluded that, the results calculated by the realizable k-epsilon model agree well with the experiment data and the realizable k-epsilon model would be utilized in the latter simulation. The agreement of the predicted data and experimental data are quite reasonable, it demonstrates that the CFD technique can be successfully applied to high-pressure water jet.

Most electronic system failures are due to thermal overstressing, and the major current trends in electronics design are adding to the thermal problem. This article introduces a new class of electronics thermal analysis tool, which uses computational fluid dynamics (CFD)techniques to predict the three-dimensional air movement and associated heat-transfer processes in electronics enclosures.

A harmonic scalar field has a Laplacian (i.e., both source-free and curl-free) gradient vector field and vice versa. Despite the good performance of spherical harmonic series on modeling the gravitational field generated by spheroidal bodies (e.g., the Earth), the series may diverge inside the Brillouin sphere enclosing all field-generating mass. Divergence may realistically occur when determining the gravitational fields of asteroids or comets that have complex shapes, which is known as the complex-boundary value problem (CBVP). To overcome this weakness, we propose a new spatial-domain numerical method based on the equivalence transformation which is well known in the fluid dynamics community: a potential-flow velocity field and a gravitational force vector field are equivalent in a mathematical sense, both referring to a Laplacian vector field. The new method abandons the perturbation theory based on the Laplace equation, and, instead, derives the governing equation and the boundary condition of the potential flow from the conservation laws of mass, momentum and energy. Correspondingly, computational fluid dynamics (CFD) techniques are introduced as a numerical solving scheme. We apply this novel approach to the gravitational field of the comet 67P/Churyumov–Gerasimenko which has an irregular shape. The method is validated in a closed-loop simulation by comparing the result with a direct integration of Newton’s formula. Both methods are consistent with a relative magnitude discrepancy at the percentage level and with a small directional difference root-mean-square value of 0.78^{circ }. Moreover, the Laplacian property of the potential flow’s velocity field is proved mathematically. From both theoretical and practical points of view, the new numerical method is able to overcome the divergence problem and, hence, has a good potential for solving CBVPs.

A thermohydrodynamic analysis, based on computational fluid dynamics (CFD) techniques, that accounts for conduction in the rotating and orbiting shaft of a hydrodynamic bearing is presented. No restrictions apply to the circumferential or axial variation of journal/shaft temperature. Dynamic cavitation effects are also introduced, such that pressures in the cavitation region are predicted rather than set. The model predictions are validated against analytical and published experimental results. For the case of a centrally located synchronous forward circular whirl orbit, it is demonstrated that the journal does not behave as a circumferentially isothermal element and that significant steady temperature differentials across the journal may occur.

Lithium-ion batteries are one of the most common energy storage systems which are widely used as a power source in portable electrical and electronic products, especially in electric and hybrid electric vehicles (HEVs) due to low self-discharge and high energy/power density. However, as a drawback, thermal instability is recognized as one of the major safety concerns and challenges in performance improvement of lithium ion battery which requires an in-depth understanding of the thermal behavior during charge and discharge cycles to improve the safety and increase the life-cycle of lithium-ion batteries. Mathematical modeling of thermal behavior as well as cooling strategy has proven to be an efficient and cost effective tool to improve the performance and extend durability of lithium-ion batteries. The thermal-electrochemical transport equations of lithium-ion battery are a set of highly coupled non-linear partial differential equations (PDEs) with non-linear source terms and Neumann type of boundary conditions in all boundaries which causes the system of equations to be highly stiff. Due to these difficulties, the procedure of numerical solution using computational fluid dynamic (CFD) techniques is highly time-consuming. In the present study, the combination of CFD techniques and electric circuit theories (Kirchhoff laws) is used to efficiently simulate thermal behavior of a lithium-ion cell both accurately and quickly. For this purpose, the whole cell regions is treated as a ladder electric circuit in which KCL and KVL equations are solved for each computational electric cell and the Butler-Volmer equation is used to find the potential difference between solid and electrolyte phases. By this approach, a set of linear system of finite difference equation can be obtained for each computational cell in which the conservation of charge equation, known as compatibility condition, is automatically satisfied. By solving this system of equations iteratively, one can obtain the distribution of electric potential and concentration throughout the cell quickly, which includes the most time consuming part of the numerical procedure. At the next step, the whole battery cell is considered as a heat source and then the specific thermal management strategy is applied to calculate temperature distribution throughout the lithium-ion cell. With the new obtained temperature field, all properties of the cell are updated and this procedure is repeated until the convergence criteria are achieved. The obtained numerical results show good agreement with P2D model by a significant improvement in computational time compared to the previous CFD techniques. It should be mentioned that, this method include the advantages of CFD techniques (accurate results) and equivalent circuit models (low computational time), simultaneously. it is obvious that, this approach is completely different compared with impedance based models— because of using exact PDEs instead of imperial base calculation of local impedances— and create very flexible platform for modeling different lithium-ion battery. It is worth noting that this numerical approach can be simply extended for 3D simulation of cell and battery pack. In addition this can be applied for thermal management of Hybrid electric vehicles with standard battery power demand profiles like US06 driving cycle.