Search

Laminar separation bubbles are one of the main critical aspects of flows at low Reynolds numbers in the range of 104 –105 . The flow separates in the laminar regime, the turbulence developing inside the recirculation region enhances the momentum transport, and the flow can reattach. Models based on the Reynolds-averaged Navier–Stokes equations suffer two of main issues: the determination of the transition onset and the level of the pressure recovery downstream of the reattachment of the flow. A model addressing both issues is presented in this paper. It is based on the γ transition model for the transition detection. The production of the turbulent kinetic energy κ has been properly enhanced thanks to a correlation found between the necessary boosting of κ and the intermittency function behavior within the bubble. The low-Mach-number and Reynolds-number flows around the Selig–Donovan 7003, Eppler 387, and NACA 0015 airfoils are analyzed. The results are compared to experimental data and large-eddy simulations available in the literature. The model can be applied to the analysis of an arbitrary airfoil without need of preliminary calculation of the transition point within the bubble.

Turbulence models are widely accepted in CFD codes in order to close Reynolds Averaged Navier Stokes equations. In the years more and more complex models were proposed to improve the reliability of...

The effect of partial slip flow on airfoil performance at high Reynolds numbers is analyzed in this paper. The link between the physical mechanism of drag reduction attained by many devices and the slip length concept has been well assessed in the literature. A slip length model is therefore here adopted in large eddy simulations to quantify the effect of slip flow on airfoil performance. The possibility to adopt a slip flow boundary condition to simulate riblets on airfoil is verified. Their effectiveness in reducing friction drag in turbulent flow has been well assessed since the end of the last century. Both theory and experiments proved that the effect of riblets only depends on the local Reynolds number. However, some experiments showed an increased effectiveness of riblets in the presence of pressure gradient. This secondary effect is still being debated and a physical explanation has not been found. This paper has the aim to provide a contribution to the understanding of this phenomenon. Large eddy simulations of flows around airfoils are proposed with an extensive analysis of riblet performance, obtained by a proper slip flow boundary condition. It is shown that riblets reduce the boundary layer displacement thickness inducing small but significant modifications to the pressure distribution, in particular in the adverse pressure gradient region. The reduced thickening of the equivalent body is the reason for the reduced form drag.

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.

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.

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.

This paper deals with the aerodynamic and aerothermodynamic design analysis of a conceptual aeroshape, designed to fit the constraints of VEGA launcher fairing and with the capability to perform an end-to-end mission from launch, orbit keeping, re-entry and landing on conventional runway. Aerodynamic and aerothermodynamic performances of the aeroshape under investigation were evaluated for the whole flight scenario by means of several numerical tools as low-order methods and computational fluid dynamics code. Results are provided in the paper and considered applicable to drive the choice of a more suitable aeroshape for a whole re-entry system development.

This paper reports a numerical investigation of the incompressible flow over a 25◦ backward-facing ramp. Different approaches and flow solvers are applied. URANS simulations have been performed by the CIRA-developed UZEN and the Open-FOAM codes. The CIRA-developed flow solver Spark-LES together with OpenFOAM have been applied to resolve the turbulent structures on a simplified geometry and a reduced computational domain resembling the separated flow region over the ramp. The activities are being performed in the framework of the CIRA-funded project SHAFT. The final aim is to investigate the control of the separation phenomenon by means of zero-net mass flux actuators. © 31st Congress of the International Council of the Aeronautical Sciences, ICAS 2018. All rights reserved.

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.

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.

The aim of this research was to assess dermal and respiratory exposure of workers to imidacloprid during manual operations with ornamental plants previously treated in greenhouses or tunnels. A total of 10 female workers, 5 in greenhouses and 5 in tunnels, were monitored for 3 or 5 consecutive days. Actual skin contamination, excluding hands, was evaluated using nine filter paper pads placed directly on the skin. To evaluate the efficacy of protective clothing in reducing occupational exposure we also placed four pads on top of the outer clothing. Hand contamination was evaluated by washing with 95% ethanol. Respiratory exposure was evaluated by personal air sampling. Respiratory dose was calculated on the basis of a lung ventilation of 15 l/min. Absorbed doses were calculated assuming a skin penetration of 10% and a respiratory retention of 100%. Dislodgeable foliar residues (DFRs) were determined during the days of re-entry in order to determine the dermal transfer factor. From the dependence of dermal exposure of hands from DFRs, a mean transfer factor was estimated to be 36.4 cm(2)/h. Imidacloprid was determined by liquid chromatography with selective mass detection and electrospray interface in all matrices analysed. Respiratory dose was 4.1+/-4.0 (0.1-14.3)% and 3.0+/-2.0 (0.6-6.9)% (mean+/-SD (range)) of the total real dose during work in tunnels and greenhouses, respectively. The estimated absorbed doses, 0.29+/-0.45 microg/kg (0.06-2.25 microg/kg) body weight and 0.32+/-0.18 microg/kg (0.07-0.66 microg/kg) body weight (mean+/-SD (range)) in tunnels and in greenhouses, respectively, were less than the acceptable operator exposure level of 0.15 mg/kg body weight and than the acceptable daily intake of 0.05 mg/kg body weight. The hands and exposed skin of all workers were found to be contaminated, indicating that greater precautions, such as daily changing of gloves and clothing, are necessary to reduce skin exposure.

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.

In a numerical simulation the choice of a turbulence model must be a compromise between physical modelling and computational cost. The CIRA RANS flow solver has been applied, by employing a large set of turbulence models, to typical aerodynamic applications for which certified experimental data are available in literature. The transonic flows over an airfoil and a wing placed in a wind tunnel, both characterized by a strong shock-boundary layer interaction with an induced separation, and the high lift flow around a multi component airfoil are taken into consideration. An evaluation, in terms of accuracy and numerical behaviour, of some common turbulence models ranging from one-equation to high order, using the same code and numerics, is presented. Satisfactory and consistent results have been achieved; the more sophisticated the turbulence model the more accurate the simulation is. The SST Menter κ – ω turbulence model has shown, for the applications investigated, the best compromise between the physical capabilities and the numerical stiffness.

The viability and accuracy of large-eddy simulation (LES) with wall modeling for high Reynolds number complex turbulent flows is investigated by considering the flow around a circular cylinder in the supercritical regime. A simple wall stress model is employed to provide approximate boundary conditions to the LES. The results are compared with those obtained from steady and unsteady Reynolds-averaged Navier–Stokes (RANS) solutions and the available experimental data. The LES solutions are shown to be considerably more accurate than the RANS results. They capture correctly the delayed boundary layer separation and reduced drag coefficients consistent with experimental measurements after the drag crisis. The mean pressure distribution is predicted reasonably well at ReD=5×105 and 106. However, the Reynolds number dependence is not captured, and the solution becomes less accurate at increased Reynolds numbers.

The paper presents the results of a research activity that aims to investigate the control effect of fast rising pulse Dielectric Barrier Discharge actuators (DBD) in high speed flow conditions. At this aim, several experimental tests have been performed on a 2D wind tunnel model in subsonic and transonic conditions to collect information concerning effects of DBD actuators on the main aerodynamic aerofoil performance. The Mach number was varied between 0.4 and 0.85 at angles of attack ranging between -2° and 8° and Reynolds numbers between Re=1.7∙10 6 and Re=2.5∙10 6 . The aerofoil geometry selected for these tests was the supercritical BAC3-11 profile with 11% of maximum thickness. During the experiments, quantitative measurements have been made through steady and instantaneous pressure sensors. In particular, 45 pressure taps and 10 high frequency pressure transducers were installed on the surface of the model. The experimental data were used to develop and validate numerical tools, able to predict the plasma behaviour in presence of convective fields and, therefore, to support the design and setting of more effectiveness DBD actuator. A Computational Fluid Dynamics (CFD) solver developed at CIRA has been used for numerical simulations. A theoretical model for dielectric barrier discharge (DBD) via bodyforce and power density terms has been implemented in order to support the experimental test campaign.

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.

This paper deals with the computational fluid dynamics analysis of a capsule entering the Earth atmosphere, at the end of a sample return mission. Several two-dimensional axissymmetric simulations have been performed to assess the flowfield environment past a sphere-cone capsule, by using non-equilibrium reacting gas approximations. Heat shield ablation and effects of flow plasma radiation on capsule aeroheating are also accounted for, also if in a non-coupled approach with the flowfield analysis. the issue of aerodynamic and aerothermodynamic performance of the entry spacecraft in the framework of a superorbital re-entry scenario is addressed.

L’uso di acque “non convenzionali”, come le acque reflue e quelle salmastre, per fini diversi da quelli potabili, quali sono quelli agricoli, si pone come un’azione concreta di recupero della risorsa e di salvaguardia ambientale, in particolare per quelle zone del Mezzogiorno d’Italia, dove la risorsa idrica costituisce un bene di grande valore. Obiettivo del presente articolo, è stato quello di stimare l’apporto idrico e di delineare quello economico che la fertirrigazione con acque reflue trattate potrebbe avere sull’agricoltura della provincia di Lecce. Sulla base degli impianti esistenti in tale ambito territoriale, sono state effettuate alcune proposte di realizzazione di sistemi di riuso individuando, per ciascun sistema, la quantità delle acque reflue depurate utilizzabili, la superficie irrigabile, le principali opere necessarie ed i relativi costi d’impianto

In un contesto di crescente bisogno di flessibilità, prontezza di risposta e qualità dell’organizzazione dei sistemi e dei processi produttivi, la gestione manuale di un sistema qualità diventa sempre più insostenibile e diviene necessaria e vitale, invece, l’adozione di sistemi automatizzati, vale a dire supportati da strumenti informatici in grado di consentire l’applicazione in tempo reale dei modelli qualità, il controllo dei processi, la raccolta e l’elaborazione delle informazioni (zero carta). In tale contesto, nella presente nota, è stato evidenziato che l’adozione dei servizi internet e il mutamento delle aziende sempre più verso modelli di “imprese estese” possono rivelarsi strategie vincenti in grado di far produrre alle imprese prodotti sempre nuovi, di qualità superiore e a prezzi più bassi.

In questa nota sulle acque reflue, viene delineato l’ambito normativo comunitario, nazionale e regionale di riferimento per la disciplina dell’utilizzo di tali acque in agricoltura. Uno dei maggiori ostacoli da superare per lo sviluppo dell’irrigazione con acque reflue trattate è proprio la normativa statale allora in vigore: normativa vaga ed imprecisa, per certi aspetti, eccessivamente rigida e di dettaglio, per altri. Dall’esame della complessiva legislazione italiana esaminata, si auspica una minore severità nella fissazione dei limiti di alcuni parametri dell’acqua utilizzabile, dal momento che limiti così restrittivi non sono previsti per acque di altra provenienza (fiumi, laghi, ecc.) e non hanno alcun riscontro negli altri paesi industrializzati.

Attualmente, una buona parte delle aziende agricole sono troppo piccole per poter sostenere adeguatamente l'industria, mancando anche di un'appropriata organizzazione e di linee produttive efficienti e moderne. Ciò, di conseguenza, determina aumenti dei costi della materia prima industriale, con qualità non sempre adeguate a mercati sempre più esigenti. Per garantire il futuro del settore si rende quindi necessario conciliare lo sviluppo delle industrie di trasformazione con la produzione agricola, con le nuove tecnologie, con l'ambiente, con le moderne esigenze e consuetudini alimentari. Allo scopo di fornire un quadro della situazione in provincia di Lecce, nella presente nota, viene innanzitutto tracciato un profilo generale della struttura del settore industriale, traendo spunto dai dati CERVED-Movimprese, dopodiché, grazie alle risultanze di una rilevazione diretta su un campione di industrie (tutte facenti parte dell'Assindustria di Lecce), viene incentrata l'attenzione sulle problematiche dei comparto in modo da cogliere, in maniera approfondita, gli aspetti critici dell’attività produttiva e della gestione dei rifiuti prodotti delle aziende esaminate.

This paper presents a numerical investigation of the flow around the Ahmed model. This is an automotive-type configuration with a rear slanted part. Experiments have been performed for different angles φ of the slanted part, and have shown a maximum of the aerodynamic drag when φ = 30◦. This angle corresponds to a change in the structure of the wake developing on the rear part of the body. Numerical simulations have been performed by employing different turbulence modelling techniques. Two angles of the slanted part, one smaller (φ = 25◦) and one bigger (φ = 35◦) than the critical angle, are considered. The main aim of the paper is to evaluate the capabilities of a CIRA Navier-Stokes flow solver in simulating a complicated turbulent flow field. The paper can also contribute to the assessment of the detached eddy simulation in reproducing the features of massively separated flows.

In the framework of the European High Lift Programme EUROLIFT II the numerical and experimental validation of high lift configurations initiated in EUROLIFT are being pursued. This present contribution describes a summary of the CFD improvements carried out in this project. The improvements cover turbulence modeling and grid generation. More sophisticated turbulence models beyond the eddy viscosity concept are evaluated as well as unsteady effects and efficiency enhancement through wall function approaches. Different techniques to reduce the number of nodes in unstructured grids have been implemented in partners grid generators, mainly through the stretching of elements and introduction of hexahedral elements. The overlapping grid technique for high lift flows are demonstrated as well. Efficiency enhancement through wall functions show that the cost can be reduced to about 50% or more. The computed results agree well with results from near wall resolved grids in the linear range but the maximum lift is over-predicted. Explicit algebraic Reynolds stress models as well as full differential Reynolds stress models improve the predictions in the maximum lift region compared to standard eddy viscosity models. Introducing stretching of unstructured grids along leading and trailing edges as well as introducing hexahedral elements can substantially reduce the number of grid nodes while maintaining the solution accuracy. Overlapping grid techniques for high lift flows show good results but some grid dependencies are observed.

Nonostante la cellulosa sia il più abbondante dei carboidrati presenti in natura, essa non si trova mai pura: nei semi del cotone è presente in quantità pari a 95% circa, nel legno è presente al 40-55%. I trattamenti convenzionali di isolamento della cellulosa dal legno si basano sull’attacco e l’eliminazione della lignina e delle emicellulose. I processi termo-meccanici comunemente utilizzati o non riescono a separare completamente la cellulosa dalle sostanze incrostanti o non riescono ad evitarne una certa degradazione. Una soluzione potrebbe essere l’uso di appropriati solventi che, penetrando nelle zone interne più cristalline della cellulosa, provocano la riduzione delle forti interazioni inter-molecolari, consentendone il recupero quasi esclusivo. Nella nota, si esaminano i principali tipi di tali solventi, evidenziandone, tra le altre, le possibilità economiche e commerciali di utilizzo.

Launch vehicles are generally characterized by a flight trajectory which covers a wide envelope of Mach and Reynolds numbers ranging respectively from transonic to hypersonic and from million tens to tenths. The wind tunnel simulation of these extremely wide flight envelopes is an hard task, and extrapolation of the experimental aerodynamic coefficients to flight conditions is often required. In this report a CIRA experience in the ground to flight extrapolation process on launch vehicles will be presented with reference to the special case of the VEGA, a new European small launcher. The experimental characterization of the VEGA external aerodynamics was performed from M=0.5 to M=7 along the flight trajectory. The ground to flight extrapolation procedure adopted was supported by CFD computations performed by CIRA with the ZEN code. Several wind tunnel conditions were rebuilt, and numerical trends with Reynolds of the aerodynamic coefficients were computed. Both the wind tunnel tests measurements and the numerical simulations permitted the individuation of the trends with Reynolds number of the aerodynamic coefficients of the launcher. Final results of the extrapolation procedure are the aerodynamic coefficients expressed as analytical functions of the Reynolds number, that allowed the computation of the aerodynamics of the model geometry at launcher full scale conditions.

Synthetic Jet technology needs robust and fast simulation tools to grow up as expected by industrial community. The activity presented in this paper is part of a research eort carried out at the Italian Aerospace Research Center (CIRA). The aim is to improve the accuracy of Reynolds-Averaged Navier-Stokes (RANS) techniques in predicting the eect of steady and unsteady flow control devices in medium/high Reynolds number compressible flows. The control of separation is studied by reproducing numerically a low Mach number 2D flow over an hump model which has been tested at NASA Langley Transonic Cryogenic Tunnel. The choice of the above case is related to the presence of an adverse pressure gradient as occurring in a classical airfoil. A boundary condition modelling for synthetic jets is presented along with comparisons between numerical and experimental data.

The purpose of this paper is to assess the capabilities of the newly developed tool U-ZEN, a code solving the Unsteady Reynolds Averaged Navier-Stokes equations. The activity is being performed within a CIRA project focusing on Flow Control; the specific goal for the CFD task is to simulate the unsteady flow phenomena due to particular fluid dynamic conditions (Mach, Reynolds, !) or to time dependent boundary conditions (e.g. flow control devices) around complex 3D configurations. The CIRA steady state flow solver ZEN (Zonal Euler Navier-Stokes) has been extended to treat unsteady problems by introducing a time discretization scheme, namely the Dual Time Stepping (DTS) technique. The validation is performed simulating unsteady flows around bluff obstacles or airfoils/wings at high angles of attack which are available experimental test cases.

Over the last few years a large effort has been devoted at CIRA to the analysis of capabilities and limits of the FWH formulations. Nevertheless, following the trend of most research institutions and industries, a new code implementing the Kirchhoff formulation has been developed and tested. The possibility of using in parallel this new code with the ones solvin the FWH equation permits to increase the CIRA capabilities in the prediction of the acoustic disturbance. The main aim of the paper is to show the reliability of the new Kirchhoff solver in rotor and propeller noise predictions.

RANS simulations of boundary layer flows with stationary and pulsating active control devices have been carried out. Two computational codes and several turbulence models have been compared to available experimental data. Two configurations have been selected: a twodimensional bump with a slot and a threedimensional circular, oscillating jet. The results for the first test case indicate that the sensitivity of the results to the choice of the RANS closure is higher for the flow without control. None of the model used allows to predict this baseline flow with satisfactory agreement. The results for the threedimensional problem are in good agreement with the measurements away from the orifice but pronounced differences are observed in the vicinity of the jet.

This paper deals with the aerodynamic and aerothermodynamic analysis of a conceptual aeroshape, designed to fit the constraints of VEGA launcher fairing and with the capability to perform an end-to-end mission from launch, orbit keeping, re-entry and landing on conventional runway. Aerodynamic and aerothermodynamic performances of the aeroshape under investigation were evaluated for the whole flight scenario by means of several numerical simulations with in-house developed and commercial codes. Compilation of the numerical Data-Base, consisting of about 170 runs, and vehicle’s aerodynamics performances are shown from low subsonic to hypersonic regime. Analysis and discussion of the results with comparisons between different numerical tools and CFD codes are given.