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The impact of urban morphology on air quality, particularly within deep canyons with longer residence times for complex chemical processes, remains insufficiently addressed. A flexible multi-box framework was used to simulate air quality at different canyon heights (3 m and 12 m). This approach incorporated essential parameters, including ventilation rates, background concentrations, photochemical schemes, and reaction coefficients. A field campaign within a deep canyon with an aspect ratio of 3.7, in Naples, Italy was conducted and used for the model evaluation. The model performance demonstrated good agreement, especially at the street level, when employing a realistic light intensity profile and incorporating volatile organic compound (VOC) chemistry. Our findings indicate that peroxyl radical production affects NO2 and O3 levels by up to 9.5% in deep canyons and underscore the significance of vertical distribution (approximately 5% variance) in health assessments and urban air quality strategy development. The model response was sensitive to changes in emissions as expected, but also, somewhat more surprisingly, to background conditions, emphasizing that policies to remove pollution hotspots must include local and broader citywide action. This work advances the understanding of air quality dynamics in deep urban canyons and presents a valuable tool for effective air quality management in intricate urban environments. [ABSTRACT FROM AUTHOR]

In the framework of innovative aerodynamics, active airfoils can be developed and exploited based on the integration of shape memory metal alloys (SMAs), allowing for surface adaptation, i.e., shape changes in response to operative thermal inputs, depending on the desired aerodynamic behavior. The purpose of thermally activated shape-changing (TASC) airfoils' improved capabilities is to offer benefits in terms of aircraft performance and fuel consumption rate. TASC airfoil design hinges upon three intertwined and nonlinear phenomena, namely the solid–fluid–thermal interactions. In this paper, in order to approach the definition of appropriate design parameters, the space of operating variables is explored for the first time by devising a finite element method simulation encompassing the equations of structural motion, energy, and turbulent Reynolds-averaged Navier–Stokes. Such a fully coupled model is then tested by implementing a sensitivity analysis for a preliminary design of a TASC/NACA airfoil. Temperature and velocity distributions are presented and discussed, including new metrics leading to aerodynamic lift calculations. When the efficiency is computed as the lift-to-drag ratio, it is found to vary nonlinearly in the 0–45 range, with the activating power feed in the 0–1000 W range. [ABSTRACT FROM AUTHOR]

One of the most interesting passive drag reduction techniques is based on the use of riblets or streamwise grooved surfaces. Detailed flow features inside the grooves can be numerically detected only by Direct Numerical Simulations (DNS), still unfeasible for high Reynolds numbers and complex flows. Many papers report the DNS of flows on microgrooved surfaces providing fundamental details on the drag reduction devices, but all are limited to plate or channel flows far from engineering Reynolds numbers. The numerical simulation of riblets and other drag reduction devices at very high Reynolds numbers is difficult to perform due to the riblet dimensions (microns in aeronautical applications). To overcome these difficulties, some models for riblet simulation have been developed in recent years, due to the data provided by DNS, experiments, and theoretical analyses. In all these models, the drag reduction is modeled rather than effectively captured; however, the analysis of some nonlocal effects on practical aeronautical configurations with riblets, requires their adoption. In this paper, the capabilities of these models in predicting riblets' performance and some interesting features of the riblets' effect on form drag and shock waves are shown. Two models are discussed and compared showing their respective advantages and limitations and providing possible enhancements. A comparison between the two models in terms of accuracy and convergence is discussed, and two new formulae are proposed to improve one of these models. Finally, a review of the results obtained by the two models is provided showing their capabilities in the analysis of the riblet effect on complex configurations. [ABSTRACT FROM AUTHOR]

Riblets are micro-grooves capable of decreasing skin-friction drag, but recent work suggests that additional benefits are possible for other components of aerodynamic drag. The effect of riblets on a fixed-wing, low-speed Unmanned Aerial Vehicle (UAV) on the total aerodynamic drag are assessed here for the first time by means of RANS simulations. Since the microscopic scale of riblets precludes their direct representation in the geometric model of the UAV, we model riblets via a homogenised boundary condition applied on the smooth wall. The boundary condition consists in a suitably tuned partial slip, which assumes riblets to be locally aligned with the flow velocity, and to possess optimal size. Several configurations of riblets coverage are considered to extract the potential for drag reduction of different parts of the aircraft surface. Installing riblets with optimal size over the complete surface of the UAV leads to a reduction of 3% for the drag coefficient of the aircraft. In addition to friction reduction, analysis shows a significant additional form of drag reduction localised on the wing. By installing riblets only on the upper surface of the wing, total drag reduction remains at 1.7%, with a surface coverage that is only 29%, thus yielding a significant improvement in the cost–benefit ratio. [ABSTRACT FROM AUTHOR]