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International audience; The application of riblets on a typical regional turboprop configuration is discussed in this paper. The effect of the riblets is modeled as a singular roughness problem by a proper boundary condition at the wall. The model, already proposed in a previous paper, is briefly described. The drag prediction capabilities are verified by showing some airfoil flow applications. Then a typical wing-body of a regional aircraft is considered. The configuration has been designed to have extended natural laminar flow in cruise conditions. Riblets are applied at flow specifications representative of cruise in combination with the natural laminar flow technology and in climb/descent conditions. A comparison of the two technologies in terms of drag reduction is presented. Their combined application can result in a cruise drag reduction of more than 20%. The resulting fuel savings during a typical operational day are evaluated.

A numerical methodology for the prediction of aerodynamics of VAWT is proposed, coupling the Beddoes-Leishman (BL) model for the airfoil’s unsteady aerodynamic coefficients prediction with the Paraschivoiu Double Streamtube (DS) aerodynamic model for VAWT. The model couples the rotational dynamics of the wind turbine modeled by DS with the aerodynamic coefficients degradation due to the local flow unsteadiness on the blade modeled by BL. The results achieved were compared with a set of experimental data available in literature and with CFD simulation, showing the importance of the non-stationary BL model for the blade’s aerodynamic coefficients prediction. Furthermore the coupled DSBL model is able to provide key information about the non-stationary aerodynamic conditions experienced on the blade for design and optimization purposes.

An assessment of the impact of cruise ship emissions while hotelling in the port of Naples has been studied by means of wind tunnel and computational fluid dynamics (CFD) models. An area of about 1.2 km2 was reproduced at a scale of 1:500 for the wind tunnel experiments. The worst but most emission scenario with three cruise ships emitting at the same time was studied. Wind blows from the south-east with a speed of 3 m/s at funnel height in neutral stability conditions of the atmospheric boundary layer. Two different values of the velocity ratio UR = 1 and UR = 4 (funnel gas velocity/wind speed) were considered. In the experiments, Ethane was used as the tracer gas and the concentration was measured at 35 receptor points inside the urban structure and at different heights. Experimental data show good agreement with those estimated by numerically solving steady Reynolds-Averaged Navier-Stokes (RANS) with the k-ω shear-stress transport (SST) turbulence model. The results were used to analyse the accuracy of the predictions of the model CALifornia Puff (CALPUFF), testing two model options: the building downwash module and the parameterisation of the dispersion coefficients. The CALPUFF results are less accurate than the CFD simulations and show a general tendency to underestimate the experimental data. The optimization process improves the performance of CALPUFF. Finally, a more comprehensive analysis of the effect of a varying UR in the range 0.25–16 was undertaken using numerical models. The research provides useful insights to improve the assessment of the impact of ship emissions in port cities.

The breakdown of the aerodynamic force is an important topic for the aerodynamic designer. The information provided by straightforward surface stress integration near field method are not sufficient, therefore, the interest in the development of far field methods arised. In this article a review of the activities carried out at the University of Naples is provided, in particular showing the potentiality and the limitations of two classes of algorithms: the thermodynamic and the vortex-force methods. Some applications and comparisons on a non-conventional wing configuration (box wing) and on an advanced turbo-prop wing-body configuration are presented.

The characterization and reproduction of tyre behaviour for vehicle modelling is a topic of particular interest both for real-time driver in the loop simulations and for offline performance optimization algorithms. Since the accuracy of the tyre forces and moments can be achieved by the accurate physical modelling of all the phenomena concerning the tyre-road interaction, the link between the tyre thermal state and the tyre frictional performance turns into a crucial factor. An integrated numerical methodology, allowing to couple the full 3D CFD (Computational Fluid Dynamics) flux within the internal chamber of the tyre with an equivalent discrete 3D structure model, is proposed with the aim to completely represent the tyre thermodynamic convective behaviour in the steady-state operating conditions. 3D CFD model enables the evaluation of the internal distribution of the gas temperature and of the thermal powers exchanged at each sub-wall in detail. This allows to increase the reliability of the tyre thermodynamic modelling with a particular reference to the proper managing of the aero-thermal flow of the brake disc impact on the rim temperature and therefore on the internal gas dynamics in terms of temperature and pressure, being able to optimize the tyre overall dynamic performance in both warm-up and stabilized thermal conditions. The steady RANS (Reynolds Averaged Navier–Stokes) simulations have been performed employing the 3D CFD model in a wide range of angular velocities with the aim to calculate the convective thermal flux distributions upon rim and inner liner surfaces. The simulation results have been then exploited to derive the convective heat transfer coefficients per each sub domain to be employed within the real-time tyre physical thermal model, with the peculiar advantage of an enhanced model reliability for thermal characteristics. To validate the proposed methodology, the tyre thermal model outputs, in terms of temperatures of internal and external layers, have been validated towards the acquired ones within the specific routine performed on tyre force and moment test bench, confirming an excellent agreement with the experimental data in the entire range of operating conditions explored.

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.

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.

The effectiveness of riblets in reducing friction drag has been well assessed by many experi- ments in flat plate and channel flow in the end of the last century. Both theory and experiments showed that the effect of riblets only depends on the local Reynolds number, however some experiments in pressure gradient flow showed increased effectiveness of riblets. This effects are still debated because a physical motivation on the effect of riblets on form drag was not provided. Recently a model based on slip length concept for riblets simulation at high Reynolds numbers has been proposed in RANS solver, providing a contribution to understanding the origin of the increased effectiveness of riblets in pressure gradient flow. In the present paper the model is extended to Large Eddy Simulation methods and applied to the analysis of airfoil flows. The analysis provides a reliable analysis of the effect of pressure gradient on riblet performance.

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.

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.

The effectiveness of the riblets, one of the most interesting drag-reduction device, is discussed in this paper. Numerical simulations by the Reynolds-averaged Navier–Stokes equations with the riblets properly taken into account are presented. Riblets are modeled as a singular roughness problem by modifying the classical Wilcox boundary condition for rough walls. The boundary condition is able to predict the flow features in the low roughness range (transitional roughness) where riblets operate. A brief discussion of the simulations performed to validate the model is first presented. Then, a complex wing–body configuration is analyzed, and the overall effect of riblets on the aerodynamic coefficients is evaluated. Calculations of a complete aircraft configuration at transonic conditions show how a proper optimized choice of the riblet height can significantly improve the drag reduction.

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.

International audience; The application of the riblets to a typical regional turbo-prop configuration is discussed in this paper. The effect of the riblets is modelled as a singular roughness problem by a proper boundary condition proposed by University of Napoli. The model is described and first its application to 2D flows is presented. Then a typical wing-body of a regional aircraft is considered. The configuration has been designed to have a natural laminar flow for a large extent of the wing in cruise conditions. Riblets are applied at flow specifications representative of cruise in combination with the laminar flow technology and in climb/descent conditions. The save of fuel achievable in a typical operative day of such an aircraft has been also estimated.

An unconventional expression of the aerodynamic force in unsteady viscous flow is pre- sented. It is based on the computation of the Lamb vector field, and it allows for a physical breakdown of the force. The unsteady aerodynamic force acting on an oscillating flat plate in incompressible viscous regime is discussed and the key role of the Lamb vector, and more generally of vorticity, on the aerodynamic force generation, is enlightened. It allows for an innovative method to exactly compute dynamic force derivatives in strongly non linear two-dimensional flows has been derived thanks to the present decomposition. The results have been confirmed analysing and post processing numerical solutions of the flow around a pitching plate and a pitching airfoil at low and high Reynolds numbers. A breakdown between thrust and drag contributions is also obtained, evidencing, for instance, the flow regions were the thrust force is generated. The obtained decomposition is compared with the classical analytical linear inviscid theories of Theodorsen & Mutchler and von Karman & Sears. Finally, a new mixed inertial-non inertial formula is proposed, more accurate when dealing with high Reynolds numbers flows.

A vorticity based exact theory for the computation and breakdown of the aerodynamic force is here applied to the analysis of three-dimensional aircraft configurations in steady transonic flow conditions by post-processing numerical CFD solutions. A rigorous and unambiguous definition of lift-induced drag in compressible flows and its distinction from the profile components (viscous and wave) has been obtained. The equation is based on field integrals of the Lamb vector field, the cross product of vorticity times velocity. It highlights the generation of the aerodynamic force in the rotational part of the flow only (mid field formula). The encountered numerical difficulties are described; they arise in particular when the freestream Mach number approaches one. 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. Applications are shown in the case of two-dimensional airfoil, elliptic wing (in transonic flow) and for the NASA CRM wing-body configuration. Comparisons with with classical drag breakdown methods based on the entropy drag concept are also presented and the improvements obtained in particular in the lift induced drag analysis are discussed.

Some aspects in the implementation of a turbulence model revealed critical for the correct prediction of the flow characteristics in the case of a low Reynolds number flow (10 4 –10 5 ) around an airfoil. In particular the treatment of the transition point setting strongly influenced the computed solution. This effect was not found in case of high Reynolds number.

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 post processing CFD solutions around wings. The possibility to extend this definition also to the case of compressible flows is investigated in this paper. In particular an exact expression of the aerodynamic force is discussed and its applicability is analyzed in case of RANS numerical solutions around an elliptic wing in subsonic and transonic conditions. A rigorous and unambiguous definition of lift induced drag is obtained. The lift induced drag still depends on the vortex force of the flow (the volume integral of the Lamb vector field), but a compressibility correction term (providing a thrust contribution) is also to be taken into account for.

The effectiveness of the riblets, one of the most interesting drag-reduction device, is discussed in this paper. Numerical simulations by the Reynolds Averaged Navier-Stokes equations with the riblets properly taken into account are presented. It is proposed to model riblets as a singular roughness problem by modifying the classical Wilcox boundary condition for rough walls. The boundary condition is able to predict the flow features in the low roughness range (transitional roughness) where riblets operate. First, the results for the incompressible flow around a flat plate and for airfoils at subsonic and transonic speed are compared with the available experimental data. Then, a complex configuration is analyzed and the overall effect of riblets on the aerodynamic coefficients evaluated. Calculations of a complete aircraft configuration at transonic conditions show how a proper optimized choice of the riblet height can significantly improve the drag reduction.

A numerical method to simulate flows in presence of laminar separation bubbles is presented and discussed in this paper. The method is based on the RANS equations, employs the κ − ω SST-LR turbulence model and makes use of an empirical criterion to individuate the point where the turbulence is activated. The method is applied to different airfoils at low and high Reynolds numbers. The low-Reynolds number flow around the SD 7003 and NACA 0012 airfoils is considered as test-case that present a long separation bubble. Then the high-Reynolds number flows around the S809 and S827 airfoils are taken into consideration. Both these airfoils present a laminar zone and very tiny bubbles over a broad range of incidences. Satisfactory results have been achieved for the low-Reynolds number cases. Good results have been obtained for the S809 airfoil imposing transition following the experimental measurements. Some discrepancies have been noted for the S827 airfoil.

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.

The development of composite scaffolds with well-organized architecture and multi-scale properties (i.e. porosity, degradation) represents a valid approach for achieving a tissue-engineered construct capable of reproducing the medium- and long-term in vitro behaviour of hierarchically complex tissues such as spongy bone. To date, the implementation of scaffold design strategies able to summarize optimal scaffold architecture as well as intrinsic mechanical, chemical and fluid transport properties still remains a challenging issue. In this study, poly ɛ -caprolactone/polylactid acid (PCL/PLA) tubular devices (fibres of PLA in a PCL matrix) obtained by phase inversion/salt leaching and filament winding techniques were proposed as cell instructive scaffold for bone osteogenesis. Continuous fibres embedded in the polymeric matrix drastically improved the mechanical response as confirmed by compression elastic moduli, which vary from 0.214 ± 0.065 to 1.174 ± 0.143 MPa depending on the relative fibre/matrix and polymer/solvent ratios. Moreover, computational fluid dynamic simulations demonstrated the ability of composite structure to transfer hydrodynamic forces during in vitro culture, thus indicating the optimal flow rate conditions that, case by case, enables specific cellular events—i.e. osteoblast differentiation from human mesenchymal stem cells (hMSCs), mineralization, etc. Hence, we demonstrate that the hMSC differentiation preferentially occurs in the case of higher perfusion rates—over 0.05 ml min –1 —as confirmed by the expression of alkaline phosphate and osteocalcin markers. In particular, the highest osteopontin values and a massive mineral phase precipitation of bone-like phases detected in the case of intermediate flow rates (i.e. 0.05 ml min –1 ) allows us to identify the best condition to stimulate the bone extracellular matrix in-growth, in agreement with the hydrodynamic model prediction. All these results concur to prove the succesful use of tubular composite as temporary device for long bone treatment.

Tissue engineering creates biological tissues that aim to improve the function of diseased or damaged tissues. In this chapter, we examine the promise and shortcomings of “top-down” and “bottom-up” approaches for creating engineered biological tissues. In top-down approaches, the cells are expected to populate the scaffold and create the appropriate extracellular matrix and microarchitecture often with the aid of a bioreactor that furnish the set of stimuli required for an optimal cellular viability. Specifically, we survey the role of cell material interaction on oxygen metabolism in three-dimensional (3D) in vitro cultures as well as the time and space evolution of the transport and biophysical properties during the development of de novo synthesized tissue-engineered constructs. We show how to monitor and control the evolution of these parameters that is of crucial importance to process biohybrid constructs in vitro as well as to elaborate reliable mathematical model to forecast tissue growth under specific culture conditions. Furthermore, novel strategies such as bottom-up approaches to build tissue constructs in vitro are examined. In this fashion, tissue building blocks with specific microarchitectural features are used as modular units to engineer biological tissues from the bottom up. In particular, the attention will be focused on the use of cell seeded microbeads as functional building blocks to realize 3D complex tissue. Finally, a challenge will be the potential integration of bottom-up techniques with more traditional top-down approaches to create more complex tissues than are currently achievable using either technique alone by optimizing the advantages of each technique.

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.

2D URANS CFD simulations were conducted to study the effect of short–time variations of wind velocity on mass transfer rate between street canyons and the atmospheric boundary layer (ABL). A street canyon with a height–to– width ratio (aspect ratio) of three was considered as a case study. The study is of practical interest since it illustrates a skimming flow regime, the regime where pollutants are less effectively exchanged between the canyon and the above atmosphere, typically found in many urban areas in Mediterranean countries. Short–time variations of wind velocity magnitude were simulated assuming a sinusoidal function with average magnitude = 4 m s −1 ; amplitude ±2 m s −1 and period from 1 to 40 s, and subsequently with short–time averaged (0.1 s, 1 s and 10 s) real world data measured with an ultrasonic anemometer (50 Hz). Mass transfer rate between the canyon and the ABL was evaluated as the rate of reduction of spatially averaged concentration of a passive pollutant, carbon monoxide (CO), in the street canyon. Results show that mass transfer rate increases with the frequency of short–time variations. In CFD studies pertaining to pollutant dispersion in street canyons, wind hourly average velocity is usually assumed as a reference value to simulate real world cases. Our results show that this input data must be completed with additional information about the extent of variation in wind intensity and its frequency in the hour.