Dissertationen zum Thema „Wheel aerodynamics“

This thesis presents the work undertaken to assess potential improvements in high performance bicycles. There are several wheel options available for elite riders to use in competition and this research has investigated the aerodynamic properties of different wheel type. The research has also developed CFD and FEA models of carbon fibre bicycle wheels to assist in the wheel improvements process. An accurate and repeatable experimental test rig was developed to measure the aerodynamic properties of bicycle wheels in the wind tunnel, namely translational drag, rotational drag and side force. Both disk wheels and spoked wheels were tested. It was found that disk wheels of different hub widths have different aerodynamic properties with the 53mm wide Zen disk wheel requiring the lowest total power of the wheels tested. There was little difference between the translational power requirements of the wheels but there was greater variation in the rotational power requirements. Compression spoked wheels of 3 and 5 spokes were found to require less power than wire spoked wheels. There was little difference between the total power requirements of the compression spoked wheels tested, with the differences at 50km/hr being less than the experimental uncertainty. The Zipp 808 wheel demonstrated considerably lower axial force than all other wheels at 10° yaw angle, confirming Zipp design intention to have optimum wheel performance between 0-20°. The Zen 3-spoke wheel showed the lowest axial drag and side force at yaw of the compression spoked wheels tested and had similar side force results to the Zipp 808. CFD models of the disk and 3-spoke wheel achieved good agreement with the experimental results in terms of translational drag. Rotational drag did not agree so well, most likely due to the turbulence model being designed for higher Reynolds number flows. A FE model of the disk wheel was validated with experimental testing. In order to simplify modelling, the FE model of the 3-spoke wheel did not include the hub, which led to a large discrepancy with experimental results for the particular loading scenario. The experimental rig and CFD models were used to develop aerodynamic improvements to the wheel and the FE models were used to identify the implication of geometric changes to the wheel structural integrity. These improvements are not reported in this thesis due to the results being commercially sensitive.

Competitive performance of an F1 race car relies upon a well designed and highly developed aerodynamic system. In order to achieve this, total understanding of the downstream wake of exposed rotating wheels is essential. Components such as bargeboards and indeed much of the front wing are developed to provide pressure gradients and vortex structures to influence the wheel wake, ensuring high energy mass-flow to the sensitive leading edge of the underfloor and eventually the rear wing. Wind tunnel testing of model-scale deformable tyres has become a common occurrence in F1 in recent years although there is a significant lack of available literature, academic or otherwise, as to their use. This work has studied in detail the aerodynamic consequences which occur from the varying sidewall bulge and contact patch region making use of several techniques. These include scanning rotating tyre profiles under load, static contact patch size measurements, five-hole pressure probe wake measurements, particle image velocimetry (PIV) and load-cell drag measurements. CFD simulations utilising two industrial codes have also been performed to support the experimental work. Coordinates representing tyre profiles under a range of on-track conditions are available for other researchers to use as a basis for CFD studies. The work presented here includes a full range of representative on-track axle heights which far exceed the more conservative range usually tested in an industrial setting for longevity reasons. The most sensitive parameters for aerodynamic testing of wheels have been identified. For development of a full car, in decreasing order of priority, the following must be correctly matched to the realistic scenario: axle height, yaw condition (without glycerol - often used to reduce friction at the expense of a compromised tyre profile), camber angle, detailed internals, high inflation pressure, through-hub flow rate and least significantly the rotation of the internal brake rotor. The study of through-hub flows revealed that the external aerodynamic effect of the brake scoop inlet varies significantly with the amount of internal restriction. The pumping effect of the brake rotor was measured to be negligible compared to the restrictive effect of its internal passages and that leads to an effect known as inlet spillage with a negative cooling drag trend, whereby the drag of the wheel assembly decreases with increased through-hub flow.

The performance of current open wheeler race cars depends heavily on the effectiveness of the aerodynamic package of which the front wing and wheels make a significant contribution. Previous investigations have focused on the aerodynamic characteristics of each of these bodies in isolation. Investigations that have considered both working in unison have conflictingly reported that the wheel presence aids or hinders the wing???s performance while the wheel???s aerodynamic performance has been neglected. In order to obtain a more thorough understanding of the interaction of a wing and wheel, experimental results were used to validate a computational model used to investigate a wing and wheel in isolation and in combination. The combined wing and wheel investigation demonstrated that three main interactions can occur, depending on the selection of wing span, angle of attack and height used, while the wheel width and track were found to have little influence. The three interacting states differ in the path that the main and secondary wing vortices take around the wheel and the subsequent variation in the combined wake structure. In general, the wing in the presence of the wheel reduced the wing???s ability to generate downforce by up to 45% due to the high pressure regions generated forward of the wheel. This was also found to alleviate the adverse pressure gradients experienced by the wing, and also reduce the drag by up to 70%. For this reason, the downforce loss phenomenon was observed to occur at a height 0.08c to 0.32c lower in comparison to the same wing in isolation, dependant on the wing span. Wheel lift and drag values were also observed to reduce in the presence of a wing by up to 65% and 38% respectively due to the influence of the wing???s flow structures have on the wake of the wheel. As a result,it was shown that the combined wing and wheel downforce and drag optima differed by up to 75% and 25% respectively to those which would be estimated if the two bodies were investigated individually and the results summed highlighting the importance of investigating these two bodies in unison.

Monoposto racecar development is routinely carried out using wheels supported not by the car suspension but by individual, externally-mounted stings. The interference effect of these stings was acknowledged but unquantified in the existing literature. Appraisal of the literature has found that the structure of a wheel wake was not understood, rendering it difficult to assess the support sting interference. These two issues were thus jointly addressed using experimental and computational methods. The two phases of this project each tested a different industrially-representative racecar wheel model. Phase One investigated a single wheel and sting combination, whilst Phase Two extended the work to include two further stings and a model racecar. Non-intrusive velocity measurements were made in the near wakes of the various combinations to extract vertical planes, perpendicular to the tunnel freestream. The measurements made behind the isolated wheels were used to investigate the main flow features of the wake. The flow surrounding an unsupported wheel was established computationally and used to evaluate the interference effects of the support sting. Different wheel support methods (three stings and the car suspension) were used to provide further insight into the sting interference effects and also the impact of sting design on those effects. Testing with and without the model racecar allowed evaluation of its effect on the wheel wake and sting interference. The main characteristics of the near-wake of an isolated wheel rotating in ground contact are proposed from analysis of the data generated in this study. A simplified model of the trailingvortex system induced in the wake of such a wheel is proposed to clarify contradictory literature. The specific interference effects of a wheel support sting are proposed with reference to the main characteristics of the wake. The mechanisms behind these effects are, where possible, identified and presented. The main impact of the support sting, and thus the root of several of the observed effects, is the modification of the axial flow through the wheel. The main effects of the presence of the car on the near-wake are proposed alongside the observation that the wake structure is not fundamentally different to that of an isolated wheel. The proposed sting interference effects are also observed in the presence of the car, albeit at a reduced level.

This study investigates the aerodynamics of nil inverted wing in ground effect, a race car wheel and the interaction between the two components, using numerical and experimental methods. The wheels were located behind the wing at flU overlap and gap of 20mm, and the wing ride height. iu the vertical direction was the primary variable. Models of 50% scale were used , giving a Reynolds number of 5.8 x 105 based on the wing chord . The Detached-Eddy Simulation model was validated against wind tunnel measurements including PIV, surface pressures and forces , where it was found to outperform a Reynolds averaged Navier-Stokes approach which used the Spalart-Allmaras turbulence model. It accurately predicted the wing vortex breakdown at low ride heights, which is of the bubble type with a spiralling tail, and the wake of the wheel. A mesh sensitivity study revealed that a finer mesh increased the amount of structures captured with the DES model, improving its accuracy.

Monoposto racecar development is routinely carried out using wheels supported not by the car suspension but by individual, externally-mounted stings. The interference effect of these stings was acknowledged but unquantified in the existing literature. Appraisal of the literature has found that the structure of a wheel wake was not understood, rendering it difficult to assess the support sting interference. These two issues were thus jointly addressed using experimental and computational methods. The two phases of this project each tested a different industrially-representative racecar wheel model. Phase One investigated a single wheel and sting combination, whilst Phase Two extended the work to include two further stings and a model racecar. Non-intrusive velocity measurements were made in the near wakes of the various combinations to extract vertical planes, perpendicular to the tunnel freestream. The measurements made behind the isolated wheels were used to investigate the main flow features of the wake. The flow surrounding an unsupported wheel was established computationally and used to evaluate the interference effects of the support sting. Different wheel support methods (three stings and the car suspension) were used to provide further insight into the sting interference effects and also the impact of sting design on those effects. Testing with and without the model racecar allowed evaluation of its effect on the wheel wake and sting interference. The main characteristics of the near-wake of an isolated wheel rotating in ground contact are proposed from analysis of the data generated in this study. A simplified model of the trailingvortex system induced in the wake of such a wheel is proposed to clarify contradictory literature. The specific interference effects of a wheel support sting are proposed with reference to the main characteristics of the wake. The mechanisms behind these effects are, where possible, identified and presented. The main impact of the support sting, and thus the root of several of the observed effects, is the modification of the axial flow through the wheel. The main effects of the presence of the car on the near-wake are proposed alongside the observation that the wake structure is not fundamentally different to that of an isolated wheel. The proposed sting interference effects are also observed in the presence of the car, albeit at a reduced level.

This diploma thesis deals with modeling and CFD calculation of aerodynamic characteristics of vehicle, influenced by loaded or unloaded tires and boundary conditions applied on this tires. These calculations are combined with three types of variable rear body shape of DrivAer vehicle. There is a complete analysis and evaluation of the effects of these factors.

Afin de faire face aux fortes températures rencontrées par les composantsen aval de la chambre de combustion, des prélèvements d’air plus frais sont réalisésau niveau du compresseur. Cet air alimente les cavités en pied de turbine et refroidiles disques rotor permettant d’assurer le bon fonctionnement de la turbine.Ce manuscrit présente une étude numérique de l’effet de ces écoulements de cavitéau pied de la turbine sur ses performances aérodynamiques. Les phénomènesd’interaction entre l’air de cavité en pied de turbine et l’air de veine principal est unphénomène encore difficilement compris. L’étude de ces phénomènes est réalisée autravers de différentes approches numériques (RANS, LES et LES-LBM) appliquéesà deux configurations pour lesquelles des résultats expérimentaux s ont disponibles.Une première configuration en grille d’aube linéaire en amont de laquelle différentesgéométries d’entrefer (interface entre plateforme rotor et stator) et débits de cavitépouvaient être variés. Une seconde configuration annulaire composée de deux étagesde turbine comprenant les cavités en pied et plus proche d’une configuration industrielle.Les pertes additionnelles associées à l’écoulement de cavité sont mesurées etétudiées à l’aide d’une méthode basée sur l’exergie (bilans d’énergie dans l’objectifde générer du travail)
In order to deal with high temperatures faced by the components downstreamof the combustion chamber, some relatively cold air is bled at the compressor.This air feeds the cavities under the turbine main annulus and cool down the rotordisks ensuring a proper and safe operation of the turbine. This thesis manuscriptintroduces a numerical study of the effect of the cavity flow close to the turbine hubon its aerodynamic performance. The interaction phenomena between the cav-ity andmain annulus flow are not currently fully understood. The study of these phenomenais performed based on different numerical approaches (RANS, LES and LES-LBM)applied to two configurations for which experimental results are avail-able. A linearcascade configuration with an upstream cavity and various rim seal geometries(interface between rotor and stator platform) and cavity flow rate avail-able. Arotating configuration that is a two stage turbine including cavities close to realisticindustrial configurations. Additional losses incurred by the cavity flow are measuredand studied using a method based on exergy (energy balance in the purpose togenerate work)

Les émissions de particules hors-échappement, en particulier celles provenant des routes, sont devenues un important contributeur à la pollution de l'air liée au trafic. Ces particules pourraient contribuer à plus de la moitié de la concentration totale dans l'air. Les présents travaux de recherche développent et valident une méthodologie numérique pour analyser la remise en suspension de particules induite par une roue en rotation. Ils se concentrent sur l'identification des zones d'émission ainsi eu sur la compréhension du rôle de l'écoulement de l'air dans le détachement et le transport des particules dans le sillage.L'étude commence par des simulations d'écoulements diphasiques dans des régimes d'écoulement sous-critiques et critiques autour de cylindres statiques et rotatifs. Cette configuration constitue un cas fondamental bien établi, étroitement lié aux écoulements induits par les roues, pour l'étude de la transition de la couche limite, de la séparation, de la topologie des sillages et le transport de particules entraînées par les structures tourbillonnaires. Les résultats mettent en évidence l'influence cruciale du choix du modèle de turbulence dans la capture des transitions laminaires-turbulentes et dans l'amélioration des prédictions de l'écoulement du sillage. La rotation du cylindre affecte de manière significative la topologie du sillage et la dispersion des particules, avec des variations en fonction du régime d'écoulement et de la taille des particules.En s'appuyant sur les résultats de l'étude de l'écoulement autour d'un cylindre, des simulations ont été réalisées pour une roue isolée en rotation sur un sol en mouvement. Les simulations ont permis de capturer les principaux phénomènes d'écoulement, notamment la séparation de la couche limite, le pompage visqueux et les tourbillons de sillage cohérents tels que les structures de jetting, de formes en fer à cheval ou d'arche. Pour la phase particulaire, un modèle de détachement des particules a été introduit afin de simuler le processus de détachement, tandis que le suivi lagrangien des particules a été utilisé pour représenter le transport des particules en interaction avec l'écoulement. Les résultats ont permis d'identifier les zones d'émission prédominantes pour différentes tailles de particules, de quantifier les taux d'émission des particules et de caractériser les trajectoires de dispersion des particules dans le sillage proche et lointain de la roue.Enfin, l'étude a examiné les effets de la vitesse (nombre de Reynolds), du rapport d'aspect de la roue et de la charge surfacique sur la remise en suspension des particules. Des vitesses plus élevées ont impliqué des structures instationnaires du sillage plus intenses, accroissant les émissions et prolongeant le transport des particules en aval de la roue. Les roues plus larges augmentent les zones de détachement et les interactions tourbillonnaires, amplifiant considérablement les émissions. Des charges surfaciques plus élevées ont augmenté la masse des particules remises en suspension tout en modifiant les zones de dépôt au sol. Les résultats de cette étude ont permis de mieux comprendre les interactions entre les particules et les tourbillons, en démontrant la contribution des structures tourbillonnaires au transport des particules dans le sillage proche et lointain de la roue, ainsi qu'au dépôt des particules au sol.Ce travail fournit une bonne compréhension des émissions de particules remise en suspension induites par le passage d'une roue, offrant une approche de simulation validée pour analyser la contribution de la remise en suspension des particules à la pollution de l'air dans divers scénarios urbains
Non-exhaust particulate emissions, particularly from road dust, have emerged as a significant contributor to traffic-related air pollution. These particles could contribute to half of the particulate concentration found in the air. The present research develops and validates a numerical methodology to analyze particle resuspension induced by a rotating wheel. It focuses on identifying emission zones and understanding the role of airflow in particle detachment and transport within the wake flows.The study begins with simulations of particle-laden flows in subcritical and critical flow regimes around static and rotating cylinders. This configuration is a well-established fundamental case closely relevant to wheel-induced flows for investigating boundary-layer transition, flow separation, flow topology, and vortex-driven particle transport. Results highlight the critical influence of turbulence model choice in capturing laminar-to-turbulent transitions and improving wake flow predictions. Cylinder rotation significantly affects wake topology and particle dispersion, with variations depending on flow regime and particle size.Building on insights from the cylinder study, simulations were conducted for an isolated rotating wheel on a moving ground. The simulations captured key flow phenomena, including boundary-layer separation,” viscous pumping'', and coherent wake vortices such as jetting, horseshoe, and arch-shaped structures. For the particle phase, a particle detachment model was introduced to simulate the detachment process, while Lagrangian particle tracking was employed to simulate particle transport within the domain. The results allowed us to identify dominant emission zones for various particle sizes, quantify particle release rates, and characterize particles' dispersion patterns in the wheel's near and far wake.Finally, the investigation has further explored the effects of velocity (Reynolds number), wheel aspect ratio, and ground dust load on particle resuspension. Higher speeds intensified unsteady wake structures, enhancing emissions and extending particle transport downstream the wheel. Wider wheels increased detachment areas and vortex interactions, significantly amplifying emissions. Higher dust loads increased the resuspended particle mass while altering ground deposition patterns. The results of this investigation enhanced the understanding of particle-vortex interactions, demonstrating the contribution of vortical structures to particle transport in the wheel's near and far wake, as well as to particle deposition on the ground.This work provides a comprehensive understanding of wheel-induced particle resuspension emissions, offering a validated simulation approach for analyzing particle resuspension contribution to air pollution across diverse urban scenarios

Cette thèse, collaboration entre Michelin et l’ONERA, propose de mettre en œuvre des simulations instationnaires URANS grâce au code Navier-Stokes elsA de l’ONERA en vue d’analyser l’écoulement complexe 3D instationnaire se développant au voisinage des roues d'un véhicule et d’identifier les mécanismes à l’origine de la production de traînée.En effet, les roues (jantes et pneumatiques) constituent un nouvel axe de recherche prometteur en aérodynamique automobile car on estime de 20% à 40% la contribution des roues et passages de roues à la traînée totale. Cependant, leur optimisation nécessite en premier lieu une compréhension complète des phénomènes aérodynamiques mis en jeu. Les analyses spatio-temporelles menées sur roue isolée et sur véhicule pour trois types de pneumatiques (lisse, rugueux, avec sillons) apportent de nouveaux éléments de compréhension sur la physique de l’écoulement. Ce travail répond notamment aux limites principales des études précédentes grâce à la description de l'écoulement sur des géométries de référence incluant des pneumatiques déformés lisses et grâce à l’étude de l’instationnarité. Les analyses spatiales permettent de décrire l’organisation des structures tourbillonnaires sur roue isolée puis autour des roues avant et arrière d’un véhicule simplifié. Les analyses temporelles facilitent quant à elles la compréhension de la dynamique de l’écoulement par la mise en évidence de la génération des tourbillons et des mécanismes d’interaction avec la carrosserie. Des validations expérimentales sont effectuées à la fois sur roue isolée et sur véhicule en soufflerie. Enfin, l’utilisation de plusieurs types de pneumatiques démontre leur capacité à modifier les caractéristiques spatio-temporelles de l’ensemble de l’écoulement et à jouer ainsi sur la puissance dissipée par le véhicule via la traînée et le moment de rotation des roues
As a collaborative task between Michelin and ONERA, this thesis aims to investigate the complex unsteady 3D flow around car wheels and to identify the mechanisms of drag production linked to this part of the car thanks to URANS unsteady numerical simulations using ONERA’s Navier-Stokes code elsA. The wheels (i.e. rims and tyres) are indeed a promising research topic in the field of car aerodynamics. The part of the total drag due to the wheels and wheelhouses is indeed estimated between 20% and 40%. The first step towards wheel optimisation is to achieve full understanding of the aerodynamic phenomena produced around them. The analysis of the flow for three types of tyres (smooth, rough, grooved), both around isolated wheels and around a simplified vehicle, brings further understanding of the flow physics. This work completes previous studies in this field thanks to the description of basic flows around smooth wheels and the study of unsteady effects. It describes the arrangement of vortical structures around an isolated wheel and around the front and rear wheels of a simplified vehicle. Moreover, the analysis of the flow unsteadiness facilitates understanding of the flow dynamics by highlighting the generation of the main vortices and the interaction phenomena with the car body. The validation of numerical models is performed with specific experiments by Michelin on both an isolated wheel and a vehicle configuration. Finally, the use of different tyres shows their ability to modify both space and time characteristics of the whole flow, thus modifying the power dissipated by the car drag and the rotation moment of the wheels

The master thesis deals with the influence of a local change of temperature due to advection from disc brake to axial velocity field close to the rotating wheel of a car. The second goal is to set parameters applicable to various wheel discs and study of the influence of these parameters to aerodynamical properties of car and thermodynamical properties of the disc brake. The thesis is numerically executed in StarCCM+. The first part focuses on theoretical background about the numerical solution and current status of research. There are described disc parameters, geometry input and solver settings in the second part. The final part deals with a comparison of velocity fields for isothermal and thermodynamical model and evaluates the influence of parameters to velocity field, aerodynamical drag and thermodynamical performance of the brake.

Sur une maquette à l’échelle 2/5ième équipée d’un diffuseur et de pneus Michelin. La géométrie du véhicule, basée sur le modèle ASMO, a été modifiée précédemment à ce travail afin d’obtenir un angle d’attaque de l’écoulement sur les roues avant et un équilibre du sillage réaliste en présence de quatre roues tournantes. Cette configuration a servi de référence dans le cadre de cette étude.Il a été mis en évidence que la configuration de base avec un sillage équilibré peut facilement être modifiée d’un point de vue aérodynamique en changeant l’état des roues (en rotation ou pas) et le type de pneumatique, en particulier sur l’essieu arrière. Cela provient d’un effet global et d’une sensibilité importante de l’équilibre du sillage aux changements de débit au soubassement. A contrario, lorsque le sillage du véhicule se trouve déséquilibré, il devient plus robuste par rapport à des perturbations de soubassement comme un changement d’état des roues ou une modification des pneumatiques. Si l’on supprime les quatre roues ou uniquement les deux roues avant, le débit de quantité de mouvement au soubassement est grandement augmenté. Par contre, si l’on supprime le diffuseur (changement important de la géométrie du véhicule), celui-ci s’en trouve nettement réduit. Dans ces deux configurations, le sillage est très fortement déséquilibré vers le sol et devient indépendant aux modifications apportées sur les roues.Il a également été mis en évidence un effet plus local du sillage des roues sur la portance et la traînée du véhicule.En effet, la zone de dépression dans le sillage des roues avant a un effet sur la portance alors que le sillage des roues arrière pilote en partie la pression au culot et donc la traînée. Il a ainsi été observé une augmentation importante de la traînée du véhicule lorsque le sillage des roues arrière, non fermé, venait en interaction directe avec le sillage du véhicule
The thesis aims to provide a better understanding of the wheel-vehicle interaction, via experimental investigations on a 2/5-th scale vehicle with an underbody diffuser and 2/5-th scale wheels equipped with Michelin tires. The vehicle geometry, based on ASMO model, was modified prior to the PhD work, in order to achieve a reasonable front wheel yaw angle, and a realistic wake balance with four rotating wheels. It is the baseline configuration in the scope of this work.The findings demonstrate that the well-balanced wake of the baseline configuration can be easily modified by different wheel states or tire modifications, especially at the rear axle. This results from a global effect of the underbody momentum modifications, i.e. a high wake sensitivity to the underbody flow. On the contrary, when the vehicle mean wake develops into a non-balanced topology, it is more robust towards underbody perturbations such as different wheel states or tire modifications. By eliminating four wheels or front wheels, the underbody momentum flux is vastly increased; by eliminating the underbody diffuser, which is a vehicle geometry modification, the underbody momentum flux is significantly reduced. In these two circumstances, one can observea robust downwash from the roof, independent of the wheel states or tire modifications. Besides, there is a more local effect of the wheels near wakes on the aerodynamic lift and drag of the vehicle. Low pressure regions in the underbody downstream the front wheels have an effect on vehicle lift. The rear wheels impose pressure conditions on the vehicle base, influencing the vehicle drag. Particularly, the merging of nonclosed mean wakes of the rear wheels with the vehicle wake can give rise to strong penalty in vehicle drag

The diploma thesis is focused on computational examination of influence of boundary condition settings in CFD software on the final aerodynamic characteristics of a vehicle. The flow analysis is carried out around a vehicle with and without the rotation of the wheels and along with the stationary and moving road. Furthermore, there is demonstrated the method of the CFD model composition and there is described the influence of rotating wheels on vehicle aerodynamic characteristics.

The aerodynamics of an exposed racing car wheel have been analysed using experimental and computational (CFD) techniques. A 40% full-scale pneumatic tyre/wheel assembly was used for the experimental investigations and the exact geometry was replicated in the CFD model. The wheel had an aspect ratio of 0.53 and the tests were conducted at a Reynolds number, based on the wheel diameter, of 2.5 x 10 . Both rotating and stationary wheels were tested with moving and fixed ground-planes, respectively. The experiments were conducted using new and existing methods of data acquisition and analysis. A non-intrusive radio telemetry system was successfully designed and developed that enabled surface static pressure data to be transmitted from a rotating wheel to a local PC. Other experimental techniques included the use of particle image velocimetry (PIV) and a pneumatic non-embedded five-hole pressure probe to investigate the flow-field about the wheel. The early flow separation, which is a characteristic of the rotating wheel, was observed in the surface static pressure distributions and PIV velocity fields. Lift and drag forces were found to decrease as a result of wheel rotation, which agreed with the work of other investigators, and the mechanisms responsible for such force reductions are postulated. The wake structures were investigated and showed weaker streamwise vorticity for the rotating wheel compared to the stationary wheel. The most important and remarkable aspect of this work was the experimental observation and subsequent CFD prediction of the rear jetting flow mechanism whose existence was previously theoretically predicted by another investigator. The PIV velocity fields clearly show the rear jetting phenomenon and this is further corroborated by a negative pressure peak in the surface pressure distributions on the wheel centreline. The effects the rear jetting phenomenon has on the wake mechanics, and hence the forces acting on the rotating wheel, are postulated.

This research contributes to the knowledge on aerodynamic wing - wheel interaction. Hereto an experimental and computational study has been performed, during which the wing ride height and the wing - wheel overlap and gap have been considered as the primary variables. The wheel drag for the combined configuration is generally lower at low ride heights and higher at high ride heights compared to the case without wing. This results primarily from changes in the flow separation over the top of the wheel - partly induced by the wing circulation - from the channel flow along the inside of the wheel and from the vortex interaction in the wheel wake. The wing downforce increases at low ride heights due to the wheel presence, but reduces at high ride heights. The modified channeling effect, vortex and separation effects govern the wing flow field, although the wheel circulation acts as an additional mechanism for downforce enhancement and limitation. The wing - wheel interaction has been studied extensively for a baseline configuration, using forces, on-surfaces pressures for the wing and wheel, oil flow and PIV data. A reduced set of data has been obtained for alternative overlap and gap settings. An increase in overlap generally leads to a reduction in wheel drag and wing downforce. A larger gap setting has relatively little influence on the wheel drag at low ride heights, but shifts the higher ride height part of the curve to lower values. The wing downforce is generally slightly lower when the gap increases. An analogy between the wing - wheel configuration and a multi-element airfoil has been used to partly explain the aerodynamic interaction between the components, based on the cross flow along the flap trailing edge. The application of a steady RANS computational approach with Spalart Allmaras turbulence model has been assessed for a baseline configuration over a range of ride heights. Qualitatively, the flow field is predicted fairly accurately, but the flow quantities correlate less satisfactory with the experiments. The downstream interaction in underpredicted, resulting in lower values for the wheel drag, in particular at high ride heights. The use of non-conformal zones around the wing is one of the causes for this discrepancy.

When it comes to vehicle aerodynamics, wheels have always a primary importance due to their high drag contribution, expecially if they cannot be shrouded. For a vehichle such as a F1 car, wheel total drag contribution reaches high percentage, such as 30-40%. This study has the purpose to investigate the aerodynamic behaviour of a non-deformable rotating flat sided wheel without hubs. The testcase is supposed to have dimensions of a 2018 F1 front tyre. A Computational Fluid Dynamics (CFD) approach, by using Open-FOAM (OF), is used to catch the main flow features, vortex structures and forces involved. A lot of time is spent to get a good mesh around the wheel with OF internal mesher due to the ground presence. Widely used Spalart-Allmaras, κ-ω SST, Realizable κ-ε codes are implemented first. Then the analysis is concentrated to κ-ω SST LM and several built-in DES models: κ-ω SST DES, Spalart-Allmaras DES, Spalart-Allmaras DDES. In the transtional model the goal is to look for laminar-turbulent boundary layer transition. In the DES/DDES approaches it is desiderable to see more detailed flow fields and a reduction of turbulent viscosity in regions where the mesh is fine enough to perform a local LES. As a consequence, comparisons between models output data and catching capabilities are made. Furthermore, the feasibility of using a DES approach with respect to RANS in automotive problems is analyzed in the case mesh grids don’t allow a fine wall resolution. Experimental data matching the testcase considered don’t exist but literature, however, provides a good agreement with the results for similar researches.

Improving the aerodynamic performance in one of the major challenges in the engineering research applied to racing bicycle. In fact, aerodynamic drag is the main source of losses in cycling and causes between 70% and 90% of total losses in flat road pace (i.e., when not climbing). Moreover, also lateral forces imposed by crosswinds play an important role because they can destabilize the bike itself. The body of the cyclist is actually the most important source of drag, because of its relevant frontal area. However, it is necessary to improve also the bike’s components aerodynamics, which account for about the 33% of the total drag. This quite relevant percentage is mainly due to the wheels and the frame design. According to Greenwell, wheel drag is responsible for 10% to 15% of total aerodynamic drag; therefore improving the design of this component can reduce the resistance of the bicycle by 2-3%. These numbers, in view of the high level required by either the today’s competitions or the bicycle market justify the effort involved in cycling components aerodynamics. The aim of this work isto assess the capability of CFD RANS simulations to predict the aerodynamic performance of modern racing bicycle wheels, and therefore build a numerical testing method to help the comparison between different solution and design. The Thesis is subdivided in five chapters after an introduction to bicycle aerodynamics and a literature review of the previous literature regarding the wheel aerodynamics; we give a look at the theory regarding the computational fluid dynamics and the different model used in this work. An initial method is build tested validated and refined showing the capabilities of the CFD to resolve the aerodynamic forces on a rotating wheel using a simpler steady-state analysis, applying the MRF method imposing a rotating frame to the region containing the wheel. Different wheels were tested and the results compared with wind tunnel results obtained by Campagnolo; using this method we compared different design and introduced a performance index to characterize the wheel performances. We performed brief analysis using and unsteady state model and a rigid body motion to compare the method with the steady model. Good agreement with experimental wind tunnel studies suggests that the approach we outline holds considerable promise. Owing to the flexibility of this methodology, it is now possible to use CFD to provide more definitive answers on some of the open questions within the competitive cycling and triathlon communities. Additional word regard the testing of an open-source code, because commercial codes are indeed expensive, we tried a simple three-spoke model with the OpenFOAM code, and highlight the pro and the cons of an open-source code. Finally, there is a brief description of different force balance layouts.
Migliorare l'aerodinamica delle biciclette da competizione è molto importante, infatti, a seconda delle condizioni, la resistenza aerodinamica è tra il 70% e il 90% della resistenza totale, oltretutto le forze laterali possono influire la stabilità del veicolo. Questo lavoro si occupa principalmente dell'aerodinamica delle ruote per biciclette da competizione nel tentativo di sviluppare un modello matematico CFD per calcolare le prestazioni di diversi profili e configurazioni, le ruote infatti sono responsabili tra il 10% e il 15% del drag di una moderna bici da competizione. Il lavoro è suddiviso in 5 capitoli, nella prima è dedicata alla letteratura scientifica sull'argomento, sull'aerodinamica della bici e delle ruote in specifico, la seconda è dedicata alla teoria delle simulazioni fluidodinamiche, poi si passa alla costruzione del metodo di lavoro, al primo modello sviluppato, i primi risultati e le conseguenti modifiche al modello e alla validazione con dati della galleria del vento, ottenendo un buon livello di validazione del metodo, in seguito ho sviluppato un modello su software opensource OpenFoam. In conclusione una breve descrizione di possibili pedane di forza utilizzabili per i test in galleria del vento.

When analyzing the aerodynamic characteristics of a road vehicle, the flow around the basic body shape is complicated by the presence of the rotating wheels. Even though on most vehicles the wheels are partially shrouded their effect on the flowfield is still considerable. Despite this, very little is understood about the flow around a rotating wheel. This thesis describes the development of a validated steady state Reynolds Averaged Navier-Stokes CFD model to investigate the flow around automobile wheels. As all the previous investigations into the aerodynamic characteristics of wheel flows had been experimental, preliminary computational studies were performed. The basis of these was the 2D circular cylinder. The effects of cylinder rotation and ground proximity were modelled, and strategies for boundary conditions and mesh topology were developed. This work was extended into 3D with the modelling of an isolated wheel, both rotating and stationary. Using existing experimental data for validation, an extensive investigation into the effects of solver numerics, symmetry planes, turbulence models, and the method of turbulent closure was performed. An optimum solver configuration was developed which comprised of the RNG k-E turbulence model with full boundary layer closure. It was accurately predicted that the rotating wheel generates less lift and drag than the equivalent stationary wheel. A number of postulated experimental flow features were captured in the final solutions. Using a parallel experimental study to provide further validation data, the CFD model was extended to incorporate an asymmetric shroud containing a wheelhouse cavity. The influence of the rotation of the wheel, the geometry of the shroud, and the thickness of the stationary groundplane boundary layer were investigated. The rotating wheel now produced more drag than the equivalent stationary wheel. Reductions in wheel drag were found with a reduction in the ride height of the shroud, and with the addition of spoilers to the lower front edge of the shroud. Increasing the stationary groundplane boundary layer thickness also reduced the wheel drag. The effects of these changes on the wheel surface pressure distributions are presented.

The design and manufacture of lightweight electric vehicles is becoming increasingly important with the rising cost of petrol, and the effects emissions from petrol powered vehicles are having on our environment. The University of Waikato and HybridAuto's Ultracommuter electric vehicle was designed, manufactured, and tested. The vehicle has been driven over 1800km with only a small reliability issue, indicating that the Ultracommuter was well designed and could potentially be manufactured as a solution to ongoing transportation issues. The use of titanium aluminide components in the automotive industry was researched. While it only has half the density of alloy steel, titanium aluminides have the same strength and stiffness as steel, along with good corrosion resistance, making them suitable as a lightweight replacement for steel components. Automotive applications identified that could benefit from the use of TiAl include brake callipers, brake rotors and electric motor components.

The aim of the master’s thesis is an investigation of volume mesh quality, turbulent models and models of rotation and their influence on aerodynamic coefficients of rotating wheels. Mesh independence study and near-wall prism layer modelling are also of high importance. Subsequently, the appropriate turbulent model is used for research of wheel rotation on drag and lift on a front and rear axle of the vehicle compared to the stationary case.

The present study focuses on investigating the aerodynamical interaction between a threeelement wing and wheel in ground effect, regarding the Formula One regulations change set for 2022 - amongst the changes is the declutter of the front wing, consequently reducing its complexity. This was accomplished by conducting a three-dimensional computational analysis, using a Detached Eddy Simulation approach, on a simplified one-quarter CAD model, built from the ground up following the regulations imposed by the FIA. The main goal was to examine how changing the front wing pressure distribution affected wheel aerodynamics, which will then influence the feeding process of the underbody, due to their proximity and subsequent flow interaction. This was done by varying the angle of attack of the second flap on the wing. The CFD study was divided into two sections: a flow analysis and a force analysis. On the flow analysis, one focused on determining the location and intensity of flow energy losses; visualizing the flow structures around the wing and wheel; and, where possible, identifying and comprehending the mechanisms behind the observed flow phenomena. On the force analysis, the transient variations of the force coefficients were examined to better understand how the unsteadiness of the vortices influenced the wing’s performance. The flow investigation indicated that the wheel wake structure is significantly influenced by the wing’s flap configuration, showing different shapes to the different geometries tested. This is mainly due to the fact that different flap configurations produce different upwash flow fields, leading to a separation point variation on top of the wheel. This variation then affects the downwash observed behind the central region of the wheel, for a vertical plane. The force investigation showed that the location of the region of instability influences the behaviour of the transient oscillations, regarding the forces acting on the wing: bearing in mind that vortex breakdown occurs near the wing’s trailing edge, higher drag force fluctuations are detected, when compared to downforce fluctuations – a shared pattern across the geometries tested.

В магистерской диссертации определены закономерности изменения тягово-эксплуатационных свойств и конструктивной безопасности автопоезда при модернизации тягово-сцепного устройства, уточнены методики определения параметров опорно-поворотного устройства с наклонной поворотной платформой, предложены конструкции тягово-сцепных устройств и представлены результаты испытаний масштабной модели автопоезда на ленточной конвейерной дорожке.
This master thesis the regularities of the change of traction and the performance and structural safety of the trains when upgrading trailer hitch, refined methods of determining the parameters of support-rotating device with a tilted turntable and the proposed design of the hitch and the results of tests of scale model train on a conveyor track.