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A 3D computational analysis has been applied to investigate direct transfer, pre-swirl systems for gas turbine cooling. Alternative computational procedures have been applied and results have been compared with measurements. Based on these validation studies, strategies for modeling such systems have been proposed. Present results suggest that sufficiently accurate predictions can be obtained using a quasi-steady analysis applying the "frozen rotor" approach for treating the interface between the stationary and rotating domains.

The global objective of this work is to show the capabilities of the Eulerian–Lagrangian spray atomization (ELSA) model for the simulation of Diesel sprays in cold starting conditions. Our main topic is to focus in the analysis of spray formation and its evolution at low temperature 255 K (-18°C) and nonevaporative conditions. Spray behavior and several macroscopic properties, included the liquid spray penetration, and cone angle are also characterized. This study has been carried out using different ambient temperature and chamber pressure conditions. Additionally, the variations of several technical quantities, as the area coefficient and effective diameter are also studied. The results are compared with the latest experimental results in this field obtained in our institute. In the meantime, we also compare with the normal ambient temperature at 298 K (25°C) where the numerical validation of the model has shown a good agreement.

The atmospheric wind turbulence over a specified time period has a strong influence on the airplane performance characteristics. Forecasting of this unsteady aerodynamic phenomenon is complex one for designing the control systems to ensure the structural safety. A novel approach is developed to assess the influence of a gust structure on the aerodynamic coefficients of an airplane. The load factor enhancement because of the discrete gust is also quantified to ensure the safety margin. The Kussner’s function is used to determine the time varying increment of gust-dependent lift produced on an airplane wing entering a sharp-edged gust. A most general gust shape is assumed for the present study with quasi-steady approximation. The turbulent viscosity across the chord wise positions are quantified to calculate the velocity fluctuations because of eddies. Determining the gust influence on the fundamental lift and drag characteristics of a commercial airplane is focused in the present investigation. It is accomplished with the help of Wagner’s function in the time domain for the gust response-dependent lift. The outcome of the numerical simulation process is fully verified using the theoretical and experimental results. Solution convergence is attained for a range of input conditions and it shows that the proposed methodology is competent to assess the gust response for various airplane systems design.

Risk management of loss of containment at facilities processing or storing liquid flammable fluids is crucial in order to ensure safe operations. To control the risk, an extensive set of safety functions are in general implemented in design, for example systems that minimize the occurrence for initiating events (e.g., spontaneous leak of flammable material due to fatigue) and measures that reduce explosion loads arising in case of delayed ignition of the dispersed fluid mixed with air. Effective ventilation of the released fluid that potentially generates an explosive atmosphere (gas and/or droplets generated from the liquid phase) is one of the crucial barrier elements to mitigate the explosion hazard. Hence, the gas explosion hazard in enclosed modules with poor ventilation is of particular concern as a flammable mixture may accumulate even for small release rates. This may result in both high likelihood of ignition and considerable explosion loads in case of ignition due to the big amount of chemical energy taking part in the combustion process relative to the size of the enclosure. Computational fluid dynamics (CFD) methods are increasingly being used to characterize the consequences of leaks of flammable fluid in complex geometries, both modeling of the initial gas dispersion process and the resulting explosion and fire loads following from the combustion process in case of ignition. This paper presents an advanced methodology based on the CFD tool OpenFOAM for detailed assessment of the transient gas dispersion process and the associated likelihood of ignition for leaks of flammable fluid inside enclosures. The objective is to understand how to optimize the design of safety functions that affect the fire and explosion risk picture. This custom made tool, denoted cloudIgnitionFoam, accounts for the transient gas leak behavior based on real-time gas detection, subsequent initiation of emergency shutdown (ESD) and blow down systems and computes ignition probability based on the transient history of the dispersed gas cloud. The consistent methodology based on the CFD technology available in OpenFOAM and its ability to present the results in detail leverages the risk-based decision process. Measures that can be assessed quantitatively includes number and types of gas detectors and their optimal positioning, ignition source isolation, gas detection system voting philosophy, capacity of depressurization system and structural integrity of explosion barriers.

For existing offshore fixed platforms it is often the case that the air gap between the deck and the sea surface is not adequate and the extreme waves will encroach on the deck resulting in large wave-in-deck loads. Factors that result in inadequate air gap are seabed subsidence, sea-level increasing due to climate change and more onerous predictions of extreme crest heights.

In this paper, a numerical approach based on NewWave theory [Tromans et al. (1991), Proc. 1st Int. Offshore and Polar Engineering Conf., Vol. 3, Edinburgh, UK, pp. 64–71] has been developed to represent the extreme wave conditions and implemented into the framework of an open source software, OpenFOAM, to predict the wave-in-deck loading. The results have been compared with published FLOW-3D simulations using Stoke’s 5th order wave theory for a simple box representing the Ekofisk platform deck in the Norwegian sector of the North Sea [Iwanowski et al. (2002), Proc. 21st Int. Conf. Offshore Mechanics and Artic Engineering, June 23–28, 2002, Oslo, Norway].

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

A three-dimensional (3D) Computational Fluid Dynamics (CFD) solver based on the gradient smoothing method (GSM) is developed for compressible flows based on previous research. The piecewise constant smoothing function with one-point integration scheme is implemented for gradient approximation of field variables and convective fluxes. The matrix-based method for gradient approximations is also developed to improve the numerical efficiency. Numerical examples of gradient approximations of several given functions have shown that the proposed GSM is more accurate and robust to mesh distortion. A transonic ONERA M6 wing is used to demonstrate the effectiveness of the proposed GSM-CFD solver.

Pollutant control is one of the key concerns in the design of buildings, for the sake of occupational health, safety and environment sustainability. In particular, risk analyses related to emergency leakage of chemicals from storage tanks or chemical processes have aroused increasing attentions in recent days, as well as the effectiveness of mitigation measures in order to eliminate, reduce and control the risks. In this paper, a CFD methodology with nonreactive chemical gases treated as passive scalars has been developed to simulate the gas dispersion across urban environments, subject to atmospheric boundary layer wind conditions. Special treatments to maintain the consistency in atmospheric boundary layer flow profiles, turbulence modeling and boundary conditions have also been accounted for. The proposed CFD methodology for gas dispersion has been implemented in the open source CFD code — OpenFOAM. It has been validated by modeling the gas dispersions for two urban-related test cases: the CODASC street canyon test case measured in a laboratory wind tunnel and the Mock Urban Setting Test (MUST) field experiment conducted in the desert area of Utah State. Effects of turbulent Schmidt number (Sc_t have been primarily addressed in this study. Statistical analyses about the discrepancies between predicted and experimental data have been carried out and statistical performance measures are used to quantify the accuracy of the proposed methodology. Simulations results from passive scalar transport equation demonstrate good agreement with experimental data, though tracer gases heavier than the atmospheric air were used in both the measurements. Furthermore, sensitivity tests also indicate that the accuracy of the simulation results is sensitive to the value of turbulent Schmidt number.

The current level of numerical methods of gas dynamics makes it possible to optimize compressors using 3D CFD models. However, the methods and means are not sufficiently developed for their wide application. This paper describes a new method for the optimization of multistage axial compressors based on 3D CFD modeling and summarizes the experience of its application. The developed method is a complex system of interconnected components (an effective mathematical model, a parameterizer, and an optimum search algorithm). The use of the method makes it possible to improve or provide the necessary values of the main gas-dynamic parameters of the compressor by changing the shape of the blades and their relative position. The method was tested in solving optimization problems for multistage axial compressors of gas turbine engines (the number of stages from 3 to 15). As a result, an increase in efficiency, pressure ratio, and stability margins was achieved. The presented work is a summary of a long-years investigation of the research team and aims at creating a complete picture of the obtained results for the reader. A brief description of the results of industrial compresses optimization contained in the paper is given as an illustration of the effectiveness of the developed methods.

The demand for high speed rail networks is rapidly increasing in developing countries like India. One of the major constraints in the design and implementation of high speed train is the braking efficiency with minimum friction losses. Recently, the aerodynamic braking concept has received good attention and it has been incorporated for high speed bullet trains as a testing phase. The braking performance is extremely important to ensure the passenger safety specifically for the trains moving at more than 120km/h. In this paper, an Indian train configuration WAP7 (wide gauge AC electric passenger, Class 7) has been assumed with the locomotive and one passenger car. Aerodynamic braking system design is done by opening a spoiler over the train to amplify the aerodynamic drag at high speeds. The magnitude of braking force depends on the position and orientation of the braking spoiler. It creates differential drag forces at various deflection angles to decelerate the trains instantaneously in proportion to the running speeds. Drag created by the braking spoiler is observed numerically with the help of CFD simulation tools for further validation through wind tunnel experiments. Striking aerodynamic results are obtained with and without braking spoilers on the passenger cars and the spoiler at $40^{\circ }--50^{\circ }$ orientation makes greater drag coefficient as compared to the other angles.

In this work, a preliminary numerical simulation of the lower urinary system using Computational Fluid Dynamics (CFD) is performed. Very few studies have been done on the simulation of three-dimensional urine through the lower urinary system. In this study, a simplified lower urinary model with rigid body assumption is proposed. The distributions of urine flow velocity, wall pressure and shear stress along the urethra are simulated based on MRI scanned uroflowmetry of a normal female. Numerical results show that violent secondary flows appear on the cross surface near the end of the urethra when the inflow rate is increased. The oscillative variation of pressure and shear stress distributions are found around the beginning section of the urethra when flow rate is at the peak value.

The aim of this study is to visualize and analyze the mucous layer effects towards the nasal airflow. Mucous layer had been neglected in previous works as it is considered a very thin layer along the nasal passageway. This paper discussed the effects in nasal airflow caused by the micrometer changes of the mucous layer thickness along the nasal passageway. Differences in maximum velocities caused by the mucous layer and visualization of the nasal airflow were studied. Computational fluid dynamics (CFD) was used to study three-dimensional nasal cavity of an adult Malaysian female. Six different models with various thickness of mucous layer within the range of 5–50 μm were implemented in the analysis with mass flow rate of 7.5 and 20 L/min. Mucous layer is assumed to be uniform, solid, and also stationary for this study. The results from all the six models were compared with the model with non-mucous effects. Based on both laminar and turbulent airflow simulations, it is shown that the addition of mucous layer thickness in analysis increased the maximum velocities at the four cross sections along the nasal cavity.

The recent advances in the computer based computational fluid dynamics (CFD) software tools in the study of airflow behavior in the nasal cavity have opened an entirely new field of medical research. This numerical modeling method has provided both engineers and medical specialists with a clearer understanding of the physics associated with the flow in the complicated nasal domain. The outcome of any CFD investigation depends on the appropriateness of the boundary conditions applied. Most researchers have employed plug boundary condition as against the pull flow which closely resembles the physiological phenomenon associated with the breathing mechanism. A comparative study on the effect of using the plug and pull flow boundary conditions are evaluated and their effect on the nasal flow are studied. Discretization error estimation using Richardson's extrapolation (RE) method has also been carried out. The study is based on the numerical model obtained from computed tomographic data of a healthy Malaysian subject. A steady state Reynold averaged Navier–Stokes and continuity equations is solved for inspiratory flow having flow rate 20 L/min representing turbulent boundary conditions. Comparative study is made between the pull and plug flow model. Variation in flow patterns and flow features such as resistance, pressure and velocity are presented. At the nasal valve, the resistance for plug flow is 0.664 Pa-min/L and for pull flow the value is 0.304 Pa-min/L. The maximum velocity at the nasal valve is 3.28 m/s for plug flow and 3.57 m/s for pull flow model.

After introduction on a new multislice computed tomography (MSCT) scanner, it has become possible to produce high-speed CT angiography (CTA) that selected preferred method for imaging in emergent vascular conditions. On the other hand, the imaging of blood vessels is often referred to as magnetic resonance angiography (MRA). Both of angiography offers the good quality of three-dimensional information of the vessels. In this study, patient specific model were reconstructed using multi-slice computed tomography (CT) and magnetic resonance imaging (MRI). The optimal transit time from intravenous injection to enhancement cardiovascular system was determined using a contrast bolus tracking technique with CT examination and phase contrast magnetic resonance angiography (PC-MRA). The purpose of this study was to describe a novel blood flow visualization and analysis in the human cardiovascular system in more detail by constructing actual three-dimensional (3D) flow and simulated model using computational flow dynamics (CFD) methods. CFD streamlines were displayed using a special illumination technique with blood pressure display, which gives a much better spatial understanding of the field's structure than ordinary constant-colored lines. Real vector display using PC-MRA was also expressed to compare with the CFD simulation. On conclusion, patient specific approach using actual blood flow with PC-MRA and CFD were effective to estimate blood flow state of the cardiovascular system.

Atherosclerotic plaque formation has been linked to haemodynamic risk factors, such as low and oscillating wall shear stresses (WSS). Experimental and numerical methods have been developed to investigate the mechanisms involved. Computational fluid dynamics (CFD) methods have the advantages of low cost and easily manageable numerical results. In order to obtain physiologically realistic results, CFD can be linked with medical imaging methods, which allow the extraction of in vivo vascular geometry and flow data to be used as input for haemodynamic simulations. Most of the image-based CFD approaches have been based on MRI, which has the disadvantages of relatively high cost and limited availability. Hence, a novel technique based on 3D ultrasound was developed with the advantages of low cost, fast acquisition and high spatial resolution. A methodology was developed to extract geometric information from the ultrasound images, reconstruct the surfaces and generate computational grids for flow simulations of the human carotid artery bifurcation. Additionally, a scheme was devised to utilize Doppler flow information for CFD boundary conditions. Accuracy and reproducibility of the combined imaging and modeling approach were evaluated in vitro and in vivo and the developed protocol was applied to normal subjects. The main conclusion of this work is the feasibility of 3D and Doppler ultrasound based CFD simulations for clinical applications. However, there are several limitations when applying this methodology in carotid bifurcations, i.e. the location of the carotid bulb relative to the jaw bone, which obscures the ultrasound path when the bifurcation is high in the neck. Future work should focus on minimizing the limitations and improve automation and reliability of image processing and reconstruction.