Search Results

Accurate turbulence modeling remains a critical problem in the prediction capability of computational fluid dynamics. One particular area lacking accurate simulations is separated turbulent flows. In this paper, the recently developed one - equation Rahman-Agarwal-Siikonen (RAS) turbulence model is used to simulate the flow of several canonical turbulent flow cases. The commercially available software ANSYS Fluent and the open source software OpenFOAM are used for the flow field calculations. It is shown that the RAS model improves the accuracy of flow simulations compared to the commonly used one - equation Spalart-Allmaras (SA) and two-equation SST k-ω turbulence models.

Since the recognition of the influence of human activity on climate change due to increasing use of fossil fuel energy, significant efforts are being devoted towards the development and implementation of renewable energy technologies that are harmless to the environment. One of the abundant energy sources is the sun. There are currently two primary ways of harvesting energy from the sun: through photovoltaic (PV) panels and through thermal collectors. With the evolution of unmanned air vehicles (UAV), as well as the growing interest in “Green Aviation,” the interest in investigating the usage of PV solar panels in certain category of aircrafts has increased in the last two decades. In a small UAV or low speed personal transportation aircraft, the wings of the airplane could possibly be covered with photovoltaic panels to harness sun's energy for propulsion.

The focus of this paper is on the numerical simulation of compressible flow in a diffusing S-duct inlet; this flow is characterized by secondary flow as well as regions of boundary layer separation. The S-Duct geometry produces streamline curvature and an adverse pressure gradient resulting in these flow characteristics. The geometry used in this investigation is based on a NASA Glenn Research Center experimental diffusing S-Duct which was studied in the early 1990's. The CFD flow solver ANSYS - Fluent is employed in the investigation of compressible flow through the S-duct. A second-order accurate, steady, density-based solver is employed in a finite-volume framework. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations are solved on a structured mesh with a number of turbulence models, namely the Spalart - Allmaras (SA), k-ε, k-ω SST, and Transition SST models, and the results are compared with the experimental data.

In U.S., the ground vehicles consume about 77% of all (domestic and imported) petroleum; 34% is consumed by automobiles, 25% by light trucks and 18% by large heavy-duty trucks and trailers. It has been estimated that 1% increase in fuel economy can save 245 million gallons of fuel/year. Furthermore, the fuel consumption by ground vehicles accounts for over 70% of CO₂ and other greenhouse gas (GHG) emissions in U.S. Most of the usable energy from the engine (after accounting for engine losses) at highway speed of 55 mph goes into overcoming the aerodynamic drag (53%) and rolling resistance (32%); only 9% is required for auxiliary equipment and 6% is used by the drivetrain. 15% reduction in aerodynamic drag at highway speed of 55 mph can result in about 5-7% in fuel saving.

Currently there are nearly 750 million ground vehicles in service worldwide. They are responsible for 50% of petroleum (oil) consumption and 60% of all greenhouse gas (GHG) emissions worldwide. The number of vehicles is forecasted to double by 2050. Therefore the environmental issues such as noise, emissions and fuel burn have become important for energy and environmental sustainability. This paper provides an overview of specific energy and environmental issues related to ground transportation. The technologies related to reduction in energy requirements such as reducing the vehicle mass by using the high strength low weight materials and reducing the viscous drag by active flow control and smoothing the operational profile, and reducing the contact friction by special tire materials are discussed along with the portable energy sources for reducing the GHG emissions such as low carbon fuels (biofuels), Lithium-ion batteries with high energy density and stability, and fuel cells.

A simple but reasonably accurate battery model is required for simulating the performance of electrical systems that employ a battery for example an electric vehicle, as well as for investigating their potential as an energy storage device. In this paper, a relatively simple equivalent circuit based model is employed for modeling the performance of a battery. A computer code utilizing a multi-objective genetic algorithm is developed for the purpose of extracting the battery performance parameters. The code is applied to several existing industrial batteries as well as to two recently proposed high performance batteries which are currently in early research and development stage. The results demonstrate that with the optimally extracted performance parameters, the equivalent-circuit based battery model can accurately predict the performance of various batteries of different sizes, capacities, and materials.

The ratio of the energy liberated during a flight to the revenue work done (ETRW) of an airplane can be employed as a key indicator to assess its environmental impact. It remains constant during the life cycle of the aircraft and is fixed by its designers. The goal of an environmentally optimum airplane is to minimize the ETRW. For an existing airplane, there are two major parameters that can greatly affect the ETRW, which are the ratio of actual payload to maximum possible payload “c” and the flight range R. The goal of this paper is to study the effect of c and R on ETRW and minimize it by using a genetic algorithm (GA). The study is performed on a Boeing 737-800 and a Boeing 747-400 aircraft. The optimization study is valuable in determining the payload and range of an existing aircraft for minimal environmental impact; it turns out that the maximum possible values of payload and range do not necessarily lead to a flight with minimal environmental impact.

Air travel continues to experience the fastest growth among all modes of transportation. Therefore the environmental issues such as noise, emissions and fuel burn (consumption), for both airplane and airport operations, have become important for energy and environmental sustainability. This paper provides an overview of issues related to air transportation and its impact on environment followed by topics dealing with noise and emissions mitigation by technological solutions including new aircraft and engine designs/technologies, alternative fuels, and materials as well as examination of aircraft operations logistics including Air-Traffic Management (ATM), Air-to-Air Refueling (AAR), Close Formation Flying (CFF), and tailored arrivals to minimize fuel burn. The ground infrastructure for sustainable aviation, including the concept of ‘Sustainable Green Airport Design’ is also covered.

The current emphasis on environment protection by reducing noise pollution has led to stricter noise standards for general aviation aircraft. As a result, there is a growing demand for a computational tool to predict the noise during the design process. A computer program, called ProRAPP, has been developed for the prediction of noise generated by propeller/rotor blades. The acoustic pressure is calculated using a form of Ffowcs Williams-Hawkings equation which is suitable for numerical implementation. For noise predictions, the observer can either move with the propeller/rotor hub or it can be fixed to the ground. Experimental data from both wind tunnel and flight tests are used to validate the numerical results.

An analytical/computational method of computing radiated noise from ducted rotor due to inflow distortion and turbulence is presented. Analytical investigations include an appropriate description of sources, the cut-off conditions imposed on the modal propagation of the pressure waves in the annular duct, and reflections at the upstream end of the duct. Far field sound pressure levels at blade passing frequency due to acoustic radiation from a small scale low speed fan are computed. Theoretical productions are in reasonable agreement with experimental measurements.