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Riblets are one of the most interesting passive drag reduction techniques. They essentially consist of streamwise grooved surfaces. Despite interest in these devices, the literature does not offer numerical simulations of riblets in the presence of pressure gradient or more generally around complex aeronautical configurations because, due to their scale length (microns), direct simulations are unfeasible. In the present paper an accurate and efficient method for the numerical simulation of riblets around complex aeronautical configurations is proposed. Riblets are modeled by a proper wall boundary condition based on the slip length concept. Slip length concept has been used by many authors in different fields; in the present paper a relation between the slip length and riblet height valid also in nonlinear range of drag reduction curve is proposed for the first time. This new boundary condition has been implemented in a standard code solving the Reynolds averaged Navier-Stokes equations. Validation tests in subsonic and transonic flows are performed comparing the results with the available experimental data. The analysis provides an interesting insight into riblets performance in the presence of the pressure gradient. Drag reduction improvement evidenced in some experiments is still debated because it seems to contradict the fact that riblet effect is confined very near to the surface (i.e., it is a local effect) and an explanation was never proposed until now. The present analysis provides a first contribution to understand why riblet performance can improve in the case of airfoil flow. [ABSTRACT FROM AUTHOR]

Convection/conduction simulations have been performed to determine flow and heat transfer phenomena in steady-state, for a plate carrying few embedded discrete heaters, exposed to by a turbulent offset cooling jet. This configuration is relevant, for example, in thermal design of vehicle body segments in aerodynamics conditions: when realized in certain alloys, their configuration will be determined based their discrete structural state prompted by supplied electrical heating. In order to approach an appropriate thermal design of the plate and obtain their precise state, the space of geometric and operating variables needs to be explored by a thorough parametric study based on the governing momentum and energy equations. In this paper, the interaction between the impinging boundary layer and the conductive effects produced by such discrete heaters is explored, giving rise to a conjugate heat transfer situation. With a flexible notation for discretized heating and temperature-dependent conduction, dimensionless heat transfer is discussed spanning the entire range of design parameters. Results report considerable variation in heat transfer: as an example, air jet over polypropylene plates brings about peak Nusselt numbers between 2000 and 4000 for an inclined configuration at Re ≈ 1 × 10 6 based on nozzle width, with related strong temperature gradients that must be addressed during design, depending on discrete heaters' configuration and properties; whereas for alumina plates the peak Nusselt numbers fall down between 600 and 750, featuring much smoother temperature variations and consequent more stable structural states. • Addressing heat transfer from finite plate thickness with discrete streamwise heating sectors for Shape Memory Alloy morphing. • Study employs a coupled steady-state dimensionless model with sensitivity analysis for solid/fluid/thermal interactions. • Analyzed local Nusselt number and heat transfer dependency on design parameters; heated sectors temperature range varies considerably. • Thermal variations may lead to operation faults as stringent thermal regimes are required for Shape Memory Alloy morphing. • Study reveals nonlinearities in discretely-source heated plate thermal regimes, laying the foundation for rational design. [ABSTRACT FROM AUTHOR]

An exact Lamb vector-based theory for the computation and decomposition of the aerodynamic force in unsteady viscous flows is presented and analyzed. This decomposition allows for a correct and straightforward computation of the dynamic force derivatives even in strongly nonlinear flows. Theory has been applied to numerical solutions around a pitching and plunging plate at low (300) and high (106) Reynolds numbers. A breakdown between thrust and drag contributions is also obtained, evidencing the flow regions where the thrust force is generated. The obtained decomposition is compared with the classical analytical linear inviscid theories. In addition, a new mixed inertial-non-inertial formula is proposed for the computation of the aerodynamic force, which is more accurate when dealing with high Reynolds numbers flows. [ABSTRACT FROM AUTHOR]

A vorticity-based exact theory for the analysis of the aerodynamic force is here applied to three-dimensional aircraft configurations in steady transonic flow by postprocessing numerical solutions. A rigorous and unambiguous definition of lift-induced drag in compressible flows and its distinction from the profile component have been obtained. The equation is based on field integrals of the Lamb vector field highlighting the generation of the aerodynamic force in the rotational part of the flow only. Encountered numerical difficulties, arisen in high-transonic flow conditions, are first described. They have been overcome by a proper treatment of the numerical integration in the shock region where the accuracy of the numerical flow solution is poorer. Thus, a new exact formula is obtained for an accurate aerodynamic force computation in high-transonic and supersonic flows. In addition, a proper identification of the shock wave wake in the numerical solution allows for the decomposition of the profile drag in viscous and wave contributions. Applications are shown in the case of airfoil, elliptic wing and for the NASA Common Research Model wing-body configuration. Comparisons with classical drag breakdown methods are presented and the improvements obtained in the lift-induced drag analysis are discussed. [ABSTRACT FROM AUTHOR]

Recently, a definition of the lift-induced drag in terms of a field integral of the Lamb vector has been proposed in case of incompressible high-Reynolds-number flow and verified by postprocessing computational-fluid-dynamics solutions around wings. The possibility to extend this definition also to the case of compressible flows is investigated in this paper. An exact expression of the aerodynamic force in three-dimensional flows is discussed; it allows for a breakdown of the aerodynamic force (both drag and lift) in its physical contributions. Its applicability is analyzed in case of Reynolds-averaged Navier-Stokes numerical solutions around an elliptic wing in subsonic and transonic conditions. A rigorous and unambiguous definition of lift-induced drag is obtained. It still depends on the vortex force of the flow (the volume integral of the Lamb vector field), but a compressibility correction term is also to be taken into account. Both viscous and wave drag components can be computed by a surface integral of the Lamb vector field in the body wake. [ABSTRACT FROM AUTHOR]

Far-field methods for aerodynamic drag calculation and breakdown around aircraft configurations by Computational Fluid Dynamics are widely adopted. Recent improvements and advances of one of these algorithms are discussed. Because these methods rely for breakdown purposes on the detection of the boundary-layer region around the body, an analysis of possible alternatives to the currently adopted boundary-layer sensor is proposed. Furthermore, a recently published study in the case of inviscid flow on the influence of the accuracy of the numerical solution at far field has been repeated in viscous flow. It shows how a far-field solution influences the computation of near-field drag, in particular, in high-lift conditions. Finally, an application to a complex high-lift three-dimensional configuration of an alternative method for the computation of the lift-induced drag is discussed. The method is based on the integration of the Lamb-vector field. [ABSTRACT FROM AUTHOR]

A new exact expression of the aerodynamic force acting on a body in steady high Reynolds number (laminar and turbulent) compressible flow is proposed. The aerodynamic force is obtained by integration of the Lamb vector field given by the cross product of vorticity times velocity. The result is obtained extending a theory developed for the incompressible case. A decomposition in lift and drag contribution is obtained in the two-dimensional case. The theory links the force generation to local flow properties, in particular to the Lamb vector field and to the kinetic energy. The theoretical results are confirmed analyzing numerical solutions obtained by a standard Reynolds Averaged Navier-Stokes solver. Results are discussed for the case of a two-dimensional airfoil in subsonic, transonic, and supersonic free stream conditions. [ABSTRACT FROM AUTHOR]

• Shape memory alloys are exploited to cast morphing appendices, to improve car's handling and fuel consumption rate. • A numerical simulation solving for thermo-fluid-structure interactions in turbulent air flow was implemented. • Variable space and a new dimensionless number were proposed for the thermally activated aerodynamics appendix. In the framework of vehicle aerodynamics, new integrated systems can be developed based on shape memory metal alloys (SMAs) capability to perform surface morphing. Such systems can be exploited to create appendices containing active composites that change shape in response to variable thermal inputs, in relation to the desired aerodynamic behavior. The purpose of these systems is to offer benefits in terms of vehicle's performance and fuel consumption rate. Even the design of the simplest geometry appendix, a finite horizontal plate aligned with a turbulent air flow, is nevertheless affected by three intertwined and nonlinear phenomena - namely the solid/fluid/thermal interactions. In order to approach the definition of appropriate design parameters, the space of operating variables must be explored by devising a numerical simulation encompassing the equation of structural motion and the energy and Reynolds Averaged Navier Stokes equations, complemented by a viable turbulence model. In this paper, a fully-coupled model encompassing all phenomena involved is tested by implementing a sensitivity analysis for a thermally activated morphing surface. Temperature, stress and velocity distributions are presented and discussed for a given geometry case. A new metrics leading to aerodynamic lift calculations is then proposed and demonstrated, that will simplify the preliminary design procedures. [ABSTRACT FROM AUTHOR]

In the frame of aerodynamic drag reduction for low-emission target, Natural Laminar Flow (NLF) control and riblets are the most interesting passive techniques. The drag breakdown in the case of riblets installed is a topical matter for understanding on which form of drag riblets act. Indeed, linear theories and flat-plate experiments show that riblets act on friction drag whereas other experiments in pressure-gradient flow revealed an increased performance of riblets that was not interpreted. A contribution to clarify this effect has been recently provided analyzing the effect of riblets on form drag in two-dimensional pressure-gradient flows. In the present paper the effect of riblets on pressure drag is discussed also in three-dimensional flows analyzing CFD solutions of the flow around an innovative regional turbo-prop aircraft (wing-body configuration) with NLF and riblets installed. For the first time, the contribution of each of two drag reduction systems is identified and a deep analysis on which form of drag riblets act in three-dimensional flow is proposed thanks to a far-field aerodynamic drag breakdown. [ABSTRACT FROM AUTHOR]

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]

A pilot plant of a solar chimney was tested for about 7 months in a suburban area near Naples (Italy) from February to August 2020. The solar chimney is 5 m high with a square-shaped collector of 4.5 m length on each side. In this paper we report and analyse data with the aim to study the fluid dynamic performances. Correlations between air flow and ambient parameters (solar irradiance, temperature, and relative humidity) are studied. A CFD model is developed to simulate the thermal and fluid dynamic behavior of the chimney. Results are useful for a better knowledge of the performances of solar chimneys and their main operating parameters such as air velocity, flow rate, temperature, and residence time that are very useful for the correct design of solar chimneys both as electrical power plants and as atmospheric pollutant abatement plants. • Experimental data of a pilot solar chimney in about six months are reported. • A fluid dynamic model correlates air velocity with ambient conditions. • The effect of air humidity is also studied. • A CFD model simulates fluid dynamic and thermal performances of the solar chimney. [ABSTRACT FROM AUTHOR]