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Öğe Assessment of a Two Equation Eddy-Viscosity Turbulence Model in Crosswind Simulation of a Heavy Ground Vehicle(Sae Int, 2022) Tunay, Tural; Drugge, Lars; O'Reilly, Ciaran J.The present study assesses the use of a two-equation eddy-viscosity turbulence model, which is a shear-stress transport (SST) k-omega turbulence model, in two-way coupled aerodynamics and vehicle dynamics simulation of a heavy ground vehicle subjected to crosswind. The obtained results are compared with the corresponding results of the improved delayed detached-eddy simulation (IDDES) conducted at similar conditions from the previous literature. The aim is to evaluate the effects of different turbulence models used in aerodynamics simulations to resolve the vehicle dynamics results in two-way coupled simulations. The results present that the absolute relative percent differences between the lateral displacement, yaw angle and roll angle results of the SST k-omega and the IDDES simulations are less than 1%, 3%, and 10%, respectively. As for the aerodynamics results, the absolute relative percent differences between the lateral force, yaw moment, and roll moment of the SST k-omega and the IDDES simulations are less than 7.3%, 8.5%, and 10.0%, respectively. The results also show that the magnitudes of the lateral force, roll moment, and yaw moment are mostly increased due to the crosswind excitations among all other force and moment components. The yaw moment presents the fastest response to the crosswind excitations.Öğe Computational and experimental investigations of the vortical flow structures in the near wake region downstream of the Ahmed vehicle model(Elsevier, 2016) Tunay, Tural; Yaniktepe, Bulent; Sahin, BesirThe present study aims to investigate flow characteristics downstream of the Ahmed vehicle model using both experimental and computational methods. Ahmed vehicle model having 1/4 scale and 25 slant angle is employed at Reynolds number of Re-H=1.48x10(4). Investigations are conducted in two parts. In the first part, Large Eddy Simulation (LES) method is used to resolve the flow structures downstream of the Ahmed model, computationally. In the second part, the technique of the particle image velocimetry (PIV) is employed to obtain the flow fields downstream of the Ahmed model. The PIV and LES investigations provides time-averaged and instantaneous velocity field results, such as vorticity contours, streamline topology, velocity profiles and spectral analysis of the flow velocity. Flow features that have been predicted by computational study are in a good harmony with the results predicted by experimental studies both on the slanted surface and in the near wake region downstream of the Ahmed model. Results present that characteristics of flow features that exist on the rear slanted surface and in the near wake region of the Ahmed model exhibit great variations in a very short distance in both stream-wise and vertical direction of the flow.Öğe Computational and experimental investigations of the vortical flow structures in the near wake region downstream of the Ahmed vehicle model(Elsevier, 2016) Tunay, Tural; Yaniktepe, Bulent; Sahin, BesirThe present study aims to investigate flow characteristics downstream of the Ahmed vehicle model using both experimental and computational methods. Ahmed vehicle model having 1/4 scale and 25 slant angle is employed at Reynolds number of Re-H=1.48x10(4). Investigations are conducted in two parts. In the first part, Large Eddy Simulation (LES) method is used to resolve the flow structures downstream of the Ahmed model, computationally. In the second part, the technique of the particle image velocimetry (PIV) is employed to obtain the flow fields downstream of the Ahmed model. The PIV and LES investigations provides time-averaged and instantaneous velocity field results, such as vorticity contours, streamline topology, velocity profiles and spectral analysis of the flow velocity. Flow features that have been predicted by computational study are in a good harmony with the results predicted by experimental studies both on the slanted surface and in the near wake region downstream of the Ahmed model. Results present that characteristics of flow features that exist on the rear slanted surface and in the near wake region of the Ahmed model exhibit great variations in a very short distance in both stream-wise and vertical direction of the flow.Öğe Effect of corrugated channel phase shifts on flow structures and heat transfer rate(Elsevier Science Inc, 2018) Tokgoz, Nehir; Tunay, Tural; Sahin, BesirThe study of quantitative visualization of flow hydrodynamics, turbulent flow characteristics and time-dependent development and disappearance of vortices in cavities of corrugated channel regarding enhancements of heat transfer is limited in the literature. For this reason, the aim of the work is to search the effects of two different phase shifts, phi (i.e. 90 degrees, 0 degrees) of corrugated channels on flow hydrodynamics and the rate of heat transfer for Reynolds numbers varying from 3 x 10(3) to 6 x 10(3). The technique of particle image velocimetry (PIV) which has the capability of observing turbulent unsteady flows and provide instantaneous velocity vectors covering defined flow fields were employed. An effective fluid mixture occurs between the core and the separated flow regions due to the occurrence of a rapid vortex shedding downstream of the entrance of cavities. Along the lower and upper sides of hollow spaces, these shedding vortices spin either counterclockwise or clockwise to stimulate entrainment. In addition, the effects of turbulent flow hydrodynamics on convective heat transfer were also investigated numerically. Numerical results of flow hydrodynamic were found to be consistent with the experimental results. Heat transfer augmentation was reported as a conclusion of different parameters including different phase shifts, phi, aspect ratios, s/H and Reynolds numbers, Re.Öğe Effects of rear slant angles on the flow characteristics of Ahmed body(Elsevier Inc., 2014) Tunay, Tural; Sahin, Besir; Ozbolat, VeliAhmed body is a simplified vehicle model which retains important features of real ground vehicles. Present study aims to investigate effects of rear slant angles (?=25°, 30° and 35°) on time-averaged and instantaneous flow characteristics downstream of the Ahmed body because angle of the rear slanted surface considerably affects the flow characteristics. The particle image velocimetry (PIV) technique is employed to measure the flow field in the symmetry plane z=0 downstream of the Ahmed body. Demonstration and detailed discussions of the flow features are provided using time-averaged velocity vectors, streamlines, vorticity and TKE contours. Three critical flow points are revealed in the wake downstream of the Ahmed body. Namely, they are focus point 1 (F1), focus point 2 (F2) and saddle point (S). Variations in slant angle ? cause shift in the locations of these critical flow points. Effects of change of slant angle ? on each critical flow point vary according to their locations in the wake. Instantaneous vorticity contours and spectral analysis of the velocity field are also provided. As a result of the spectral analysis, a single dominant frequency location is only detected for ?=25°, on the other hand two dominant frequency locations are detected for ?=30° and 35° in the wake. Mean stream-wise and vertical velocity components are compared with available data in the literature. Although there are some discrepancies between the present and previous results at certain locations in the flow field, general agreement between these results is reasonably good when taking the difference between Reynolds numbers of the two studies into account. © 2014 Elsevier Inc.Öğe Experimental investigation of the flow around a simplified ground vehicle under effects of the steady crosswind(Elsevier Science Inc, 2018) Tunay, Tural; Firat, Erhan; Sahin, BesirCrosswinds which stem from on-road flow conditions can deteriorate a ground vehicle's driving performance. In spite of the numerous studies investigating aerodynamics of the ground vehicles in the previous literature, there is still a need for thorough understanding of the underlying flow phenomena related to crosswind sensitivity of the ground vehicles. Therefore, the present study is aimed to investigate characteristics of the flow features around the ground vehicles under steady crosswind conditions within a range of yaw angles 0 degrees <= beta <= 15 degrees using the Ahmed vehicle model with rear slant angles of alpha = 25 degrees and 35 degrees. Throughout the investigations, flow visualizations using dye injection technique and velocity measurements using particle image velocimetry PIV technique are conducted. The Reynolds number of the flow which is based on the free stream flow velocity U = 200 mm/s and height of the model H = 72 mm is Re-H = 1.4 x 10(4). Results are presented in terms of time averaged vorticity contours and streamline patterns together with velocity magnitude ((< u >(2)+ < w >(2))(1/2)/U) of the flow fields. Additionally, turbulence quantities such as Reynolds stresses < u'w' >/U-2 and turbulent kinetic energy TKE are presented and discussed in details. Results of the present study show that characteristics of the flow features in the near wake region downstream of the Ahmed model are very sensitive to the effects of the crosswind.Öğe Experimental investigation of the flow around a simplified ground vehicle under effects of the steady crosswind(Elsevier Science Inc, 2018) Tunay, Tural; Firat, Erhan; Sahin, BesirCrosswinds which stem from on-road flow conditions can deteriorate a ground vehicle's driving performance. In spite of the numerous studies investigating aerodynamics of the ground vehicles in the previous literature, there is still a need for thorough understanding of the underlying flow phenomena related to crosswind sensitivity of the ground vehicles. Therefore, the present study is aimed to investigate characteristics of the flow features around the ground vehicles under steady crosswind conditions within a range of yaw angles 0 degrees <= beta <= 15 degrees using the Ahmed vehicle model with rear slant angles of alpha = 25 degrees and 35 degrees. Throughout the investigations, flow visualizations using dye injection technique and velocity measurements using particle image velocimetry PIV technique are conducted. The Reynolds number of the flow which is based on the free stream flow velocity U = 200 mm/s and height of the model H = 72 mm is Re-H = 1.4 x 10(4). Results are presented in terms of time averaged vorticity contours and streamline patterns together with velocity magnitude ((< u >(2)+ < w >(2))(1/2)/U) of the flow fields. Additionally, turbulence quantities such as Reynolds stresses < u'w' >/U-2 and turbulent kinetic energy TKE are presented and discussed in details. Results of the present study show that characteristics of the flow features in the near wake region downstream of the Ahmed model are very sensitive to the effects of the crosswind.Öğe Large Eddy Simulation of the Biased Wake Flow Downstream of Circular Cylinders with a Slit(2023) Tunay, TuralThe characteristics of flow around slit-inserted cylinders were investigated using the three-dimensional large eddy simulation (LES). In the investigations, three different slit width-to-cylinder diameter ratios, i.e., s/D = 0.1, 0.2 and 0.3, together with regular cylinder were used. Slits were placed inside the cylinders with a zero-inclination angle, ? = 0o. The Reynolds number of the flow was ReD = 3900 based on the cylinder diameter, D, and free stream velocity, U?. The results presented that the jet flow emerging from the slits deviated in crossflow direction forming a biased wake flow downstream of the slit cylinders. Compared with the regular cylinder, relative per cent reductions in drag coefficients of the slit cylinders with s/D = 0.1, 0.2 and 0.3 were 3.1%, 11.3% and 6.5%, respectively. The rates of turbulence quantities in downstream wakes of the slit cylinders were reduced. Formations of shear layers in the downstream wake changed drastically as the slit width-to-diameter ratio, s/D, increased.Öğe Numerical Investigation of the Passive Flow Control Around a Circular Cylinder(2023) Tunay, TuralThe effects of a perforated cylinder on the passive flow control around a circular cylinder mounted on a wall were investigated. The perforated cylinder was placed outside of the single circular cylinder concentrically. The large-eddy simulation was used to resolve the flow field. The study was aimed at both reducing the drag coefficient of the single cylinder and controlling the fluctuating forces acting on the single cylinder caused by vortex shedding in the downstream wake. The results showed that the structure of the downstream wake flow of the single cylinder changed significantly after placing the perforated cylinder. For example, von Karman vortices disappeared, and the maximum magnitude of turbulent kinetic energy, TKE, in the downstream wake was reduced. The time-averaged drag coefficient of the single cylinder was decreased by 69%. In addition, the maximum value of the lift coefficient of the single cylinder was reduced by eight times when the perforated cylinder was placed outside the single cylinder.Öğe On coupling methods used to simulate the dynamic characteristics of heavy ground vehicles subjected to crosswind(Elsevier, 2020) Tunay, Tural; Drugge, Lars; O'Reilly, Ciaran J.Ground vehicles often encounter turbulent flows with wide range of scales, e.g. crosswind gusts, when moving on-road conditions. Crosswinds can be considered as an important factor in heavy vehicle's roll-over accident due to their relatively high center of gravity and lateral surface area. However, there are few studies which investigate effects of crosswinds on heavy vehicles. Furthermore, existing studies have generally focused on lateral or yaw dynamics of heavy vehicles and neglected their roll dynamics. Therefore, effects of crosswinds on heavy ground vehicles should be understood in all aspects in order to design less wind-sensitive vehicles especially at early stages of their design processes. Inherently, crosswind studies require a multidisciplinary approach which involves coupling between aerodynamics and vehicle dynamics. In the present study, investigation of effects of the coupling methods, e.g. one-way and two-way couplings, between aerodynamics and vehicle dynamics simulations are aimed by considering both lateral and roll dynamics of heavy vehicles which are subjected to crosswind gust. Vehicle dynamics and aerodynamics results are presented. Results of the one-way coupled simulations, in general, overestimate the absolute maximum values of the vehicle dynamics results. However, differences in lateral displacement results Delta y(max) are less than 0.2 m for the studied case.Öğe The Effects of Different Drivers' Steering Inputs on the Response of Heavy Ground Vehicles to Crosswind Disturbances(Mdpi, 2024) Tunay, Tural; Drugge, Lars; O'Reilly, Ciaran J.Featured Application The control, stability, or even safety of a vehicle can be influenced by crosswinds. The findings of the current study can be helpful for the reliable design of ground vehicles with less wind sensitivity early in their development processes. The development of lateral disturbance compensation algorithms and autonomous vehicles can also benefit from the results of the study.Abstract The general approach in the previous studies was to ignore the driver's steering contribution to a vehicle while investigating the interactions between crosswind and vehicle. Therefore, the goal of this study is to find out how steering inputs by drivers affect a heavy-ground vehicle's dynamic reaction to crosswinds. In the investigation, a two-way interaction between vehicle dynamics and aerodynamic simulations was employed. The steering inputs of drivers were modelled using a driver model taken from the previous literature that is able to reproduce the steering responses of a human driver. The study's findings demonstrated that the steering inputs made by drivers significantly impacted how the vehicle responded to crosswinds. For instance, the greatest lateral displacement of the least skilled driver (Driver 1) was around 1.53 times the greatest lateral displacement of the most skilled driver (Driver 3) at the delay time of t delta,delay = 0.5 s in the steering input. Additionally, the maximum lateral displacement results of Driver 1 and Driver 3 at t delta,delay = 1.0 s became 1.39 and 1.56 times greater than their maximum lateral displacement results at t delta,delay = 0.5 s. Similarly, the total steering inputs of Driver 1 and Driver 3 at t delta,delay = 1.0 s were 1.4 and 2.2 times greater than their total steering inputs at t delta,delay = 0.5 s, respectively. In general, the results of a driver who is more skilled than Driver 1 (Driver 2) fall in between the respective results of Driver 1 and Driver 3. On the other hand, each driver's total steering inputs at t delta,delay = 0.5 s were roughly the same as their total steering inputs at t delta,delay = 0 s. In all delay scenarios for the start of the driver's steering inputs, the drivers' steering inputs amplified the yaw moment applied to the vehicle. Meanwhile, they diminished the lateral force and roll moment.Öğe The Significance of Roll on the Dynamics of Ground Vehicles Subjected to Crosswind Gusts by Two-Way Coupled Simulation of Aero- and Vehicle Dynamics(Springer International Publishing Ag, 2020) Tunay, Tural; O'Reilly, Ciaran J.; Drugge, LarsImprovements in vehicle technologies in recent decades enable the use of lighter materials and the development of control systems for autonomous vehicles. However, these improvements lead to a need for better understanding of how flow phenomena affect crosswind stability of ground vehicles which will enable the design of the less wind-sensitive vehicles. Therefore, the present study investigates the significance of roll on the dynamics of ground vehicles subjected to crosswind gusts. It includes a multidisciplinary approach in which there is a two-way coupled simulation between aerodynamics and vehicle dynamics equations. As a result of the investigations, significant differences have been found between the computations considering no-roll and roll motions.Öğe Two-way coupled aerodynamics and vehicle dynamics simulations of a heavy ground vehicle subjected to crosswind of various frequencies(Sage Publications Ltd, 2023) Tunay, TuralThe present study investigates the dynamic characteristics of a heavy ground vehicle subjected to crosswind with various frequencies using two-way coupled simulations between aerodynamics and vehicle dynamics, including the driver's steering inputs. Four different reduced frequencies of crosswind, which are equal to 4.2, 2.1, 1.3 and 0.9, are used. The results show that the absolute maximum magnitudes of the vehicle's lateral dynamic and aerodynamic characteristics increase inversely proportional with the reduced frequencies of crosswinds without the driver's steering input. However, when the driver's steering input is included in the vehicle's response to the crosswind disturbances, the vehicle's lateral dynamic characteristics increase by the largest amount for reduced frequencies of 1.3 and 2.1. Furthermore, for a reduced frequency of 0.9, the driver's steering inputs attenuate the unfavourable amplifications in the vehicle's lateral dynamic characteristics. In the present study, the reasons for the increase in the vehicle's lateral dynamic characteristics in the cases of reduced frequencies equal or greater than 1.3 with the driver's steering input are explained. Additionally, the results show that the vehicle is not controlled within the 0.5 m lateral margins of the road when the steering starts with a time delay of 1.0 s for reduced frequencies equal to or lower than 2.1.Öğe Two-way coupled aerodynamics and vehicle dynamics simulations of a heavy ground vehicle subjected to crosswind of various frequencies(Sage Publications Ltd, 2023) Tunay, TuralThe present study investigates the dynamic characteristics of a heavy ground vehicle subjected to crosswind with various frequencies using two-way coupled simulations between aerodynamics and vehicle dynamics, including the driver's steering inputs. Four different reduced frequencies of crosswind, which are equal to 4.2, 2.1, 1.3 and 0.9, are used. The results show that the absolute maximum magnitudes of the vehicle's lateral dynamic and aerodynamic characteristics increase inversely proportional with the reduced frequencies of crosswinds without the driver's steering input. However, when the driver's steering input is included in the vehicle's response to the crosswind disturbances, the vehicle's lateral dynamic characteristics increase by the largest amount for reduced frequencies of 1.3 and 2.1. Furthermore, for a reduced frequency of 0.9, the driver's steering inputs attenuate the unfavourable amplifications in the vehicle's lateral dynamic characteristics. In the present study, the reasons for the increase in the vehicle's lateral dynamic characteristics in the cases of reduced frequencies equal or greater than 1.3 with the driver's steering input are explained. Additionally, the results show that the vehicle is not controlled within the 0.5 m lateral margins of the road when the steering starts with a time delay of 1.0 s for reduced frequencies equal to or lower than 2.1.Öğe Two-Way Coupled Aerodynamics and Vehicle Dynamics Crosswind Simulation of a Heavy Ground Vehicle in Winter Road Conditions(Springer Science and Business Media Deutschland GmbH, 2022) Tunay, Tural; Drugge, Lars; O’Reilly, Ciarán J.The present study investigates the dynamic characteristics of a heavy ground vehicle that is subjected to crosswind on winter roads by two-way coupled simulations of aerodynamics and vehicle dynamics. Three different road friction coefficients, ? = 1.0, 0.3 and 0.15, were investigated, representing dry, snowy, and icy road conditions, respectively. Results show that the lateral displacements of the vehicle on the icy road are 13%, 20% and 26% more than the corresponding lateral displacements of the vehicle on the dry road at maximum crosswind velocities of w cw,max = 3.5 m/s, 4.5 m/s and 5.5 m/s, respectively. Additionally, at w cw,max? 4.5 m/s and a crosswind length of three times the vehicle length, corresponding to the reduced frequency of k = 2.1, the crosswind might cause the driver to lose control of the vehicle, causing it to cross the road’s lateral margins in all road conditions which could result in an accident. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.
