Energy

A Geometrical Criterion for Absolute Instability in Separated Boundary Layers

Avanci, MP
Rodriguez, D
Alves, LSB
2019

Laminar separation bubbles on airfoils and low-pressure turbines are generally expected to be dominated by convective inflectional instability. However, absolute instability is possible under certain circumstances, which may lead to important changes in the laminar-turbulent transition, reattachment processes, and their impact on the aerodynamics. This paper revisits the absolute/convective instability properties of different families of boundary-layer velocity profiles with a reversed flow region. A new methodology is employed in the analysis, which incorporates an additional...

Dynamics of the Large-Scale Structures and Associated Noise Emission in Airfoil Slats

Souza, DS
Rodriguez, D
Himeno, FHT
Medeiros, MAF
2019

We investigate the slat narrowband peak noise generating mechanism. Unsteady flow data were generated by a lattice-Boltzmann-based commercial code for four configurations, accounting for variations of the airfoil angle of attack and slat overlap. Comparison with experimental results indicates that the aspects of the flow field relevant for the generation of the narrowband peaks were accurately captured. Frequency-domain proper orthogonal decomposition (POD) is applied to identify dominant large-scale structures in the frequency range dominated by the peaks. The combined use of the...

Enhancement of Disturbance Wave Amplification Due to the Intrinsic Three-Dimensionalisation of Laminar Separation Bubbles

Rodriguez, D
Gennaro, EM
2018

Previous studies demonstrated that laminar separation bubbles (LSBs) in the absence of external disturbances or forcing are intrinsically unstable with respect to a three-dimensional instability of centrifugal nature. This instability produces topological modifications of the recirculation region with the introduction of streamwise vorticity in an otherwise purely two-dimensional time-averaged flows. Concurrently, the existence of spanwise inhomogeneities in LSBs have been reported in experiments in which the amplification of convective instability waves dominates the physics. The co...

The Effect of Compressibility on the Primary Global Instability of Unforced Laminar Separation Bubbles

Gennaro, EM
Souza, BDP
Rodriguez, D
2019

Laminar separation bubbles present a three-dimensional self-excited instability mechanism which leads to the appearance of spanwise-periodic structures. In incompressible flow, this mechanism was found to become active at conditions in which wave-like, two-dimensional perturbations are only convectively unstable. In the absence of continuous external excitation, the three-dimensional instability is expected to dominate the flow dynamics and initiate the laminar-turbulent transition. This work extends previous analyses by incorporating the effect of compressibility at subsonic...

Análise da Transferência da Energia Entre o Escoamento Base e os Modos globais de uma Bolha de Separação Laminar

Romano, AC
Gennaro, EM
Rodríguez, DA
2020

A transição do escoamento do regime laminar ao turbulento está geralmente associada com instabilidades do escoamento laminar de referência. Pequenas perturbações crescem em amplitude, extraem energia do escoamento médio, e geram estruturas de amplitudes finitas que iniciam, através de interações não lineares, o processo de transição.

The Dynamics of the California Electric Grid Mix and Electric Vehicle Emission Factors

Zhang, Xingrui
Martin, Elliot
Shaheen, Susan
2025

Electric vehicle (EV) emissions occur when a vehicle is charged and are based on the mix of power sources used during that period. The rapid growth of solar and wind energy has introduced a high degree of variability in the emissions of the grid for both diurnal and annual periodicities. Growth in solar energy has been particularly prominent in California. Using grid mix data spanning April 2018 to April 2023 from the California Independent System Operator (CAISO) and power source emission factors, we evaluate the grid mix at 5 min intervals and estimate the emission factors based on the...

Highway Electrification: An Exploration of Energy Supply Implications

Wang, Quanlu
Sperling, Daniel
1987

The objective of this preliminary report is to explore the energy supply opportunities and implications of electrifying highways. An important assumption in this report is that the technology and general cost structure for generating and storing electricity does not change significantly in the future. In other words, we ignore the possible use of super conductive materials to store electricity during off-peak times, which, if feasible, would greatly reduce average electricity costs. A future report will examine the opportunities and implications of breakthroughs in superconductivity.The...

Supercharged? Electricity Demand and the Electrification of Transportation in California

Burlig, Fiona, PhD
Bushnell, James PhD
Rapson, David PhD
Wolfram, Catherine PhD
2020

The rapid electrification of the transportation fleet in California raises important questions about the reliability, cost, and environmental implications for the electric grid. A crucial first element to understanding these implications is an accurate picture of the extent and timing of residential electricity use devoted to EVs. Although California is now home to over 650,000 electric vehicles (EVs), less than 5% of these vehicles are charged at home using a meter dedicated to EV use. This means that state policy has had to rely upon very incomplete data on residential charging use. This...

Vehicle Manufacturing Futures in Transportation Life-cycle Assessment

Chester, Mikhail
Horvath, Arpad
2011

Vehicle manufacturing effects are critical life-cycle components in the total costs of vehicle travel and future manufacturing processes should be evaluated for travel forecasts. With efforts to introduce lightweight materials, increased fuel economy, and new technologies such as electric vehicles, understanding the energy and environmental effects of these expected vehicles is critical. Current vehicle manufacturing energy use and greenhouse gas emissions are summarized from existing research for passenger (conventional gasoline vehicles, hybrid electric vehicles, aircraft, high-speed...

Energy and Greenhouse Impacts of Biofuels: A Framework for Analysis

Kammen, Daniel M.
Farrell, Alexander E.
Plevin, Richard J.
Jones, Andrew D.
Nemet, Gregory F.
Delucchi, Mark A.
2008

In this paper, we review some of the basic energy balance and climate change impact issues associated with biofuels. For both the basic energy and greenhouse gas balances of producing and using a range of fuels, and for the increasingly debated and important issues of nongreenhouse gas impacts such as land, fertilizer, and water use, we conclude that an improved framework for the analysis and evaluation of biofuels is needed. These new methodologies and data sets are needed on both physical and socioeconomic aspects of the life-cycle of biofuels. We detail some of components that could be...