Energy

The size and behavior of laminar separation bubbles is strongly related to the laminar-to-turbulent transition process that takes place downstream of the separation of the laminar boundary layer. Wind-tunnel experiments and numerical simulations in which external fluctuations are imposed show a clear dominance of instability waves of convective nature in the transition process. On the other hand, stability analysis demonstrate the existence of a self-excited mechanism that introduces a three-dimensionalization of the recirculation region. This paper studies the co-existence of both...

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...

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...

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...