| 1. |
- Gaylard, Adrian Philip, et al.
(författare)
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A Computational Investigation of Ground Simulation for a Saloon Car
- 2014
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 7:1, s. 111-123
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Tidskriftsartikel (refereegranskat)abstract
- Automotive aerodynamics measurements and simulations now routinely use a moving ground and rotating wheels (MVG&RW), which is more representative of on-road conditions than the fixed ground-fixed wheel (FG&FW) alternative. This can be understood as a combination of three elements: (a) moving ground (MVG), (b) rotating front wheels (RWF) and (c) rotating rear wheels (RWR). The interaction of these elements with the flow field has been explored to date by mainly experimental means.This paper presents a mainly computational (CFD) investigation of the effect of RWF and RWR, in combination with MVG, on the flow field around a saloon vehicle. The influence of MVG&RW is presented both in terms of a combined change from a FG&FW baseline and the incremental effects seen by the addition of each element separately.For this vehicle, noticeable decrease in both drag and rear lift is shown when adding MVG&RW, whereas front lift shows little change. The same trends are seen in both CFD and experimental data.The addition of MVG alone increases both drag and front lift, whereas rear lift decreases significantly. The addition of RWF alone has little effect on the global results (aside from lift), whereas the addition of RWR alone decreases both drag and rear lift significantly. Combining the incremental changes produces values that align well to the MVG&RW case, with the exception of front lift.This shows similar trends to previously published work, both the noticeable drag decrease due to the addition of MVG&RW, and the contributions of the individual components.
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| 2. |
- Bolzon, Micheal, 1990
(författare)
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Modeling Tire Tread Features
- 2020
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- This study details an investigation into the accuracy of a recently proposed tire rotation simulation approach, termed the "MRFg"method. Physical experiments and computational fluid dynamics (CFD) simulations were conducted on a sedan-type passenger vehicle with various tire treads and rims. Furthermore, the effects of the wind tunnel geometry on the method's accuracy was investigated. The experimental data consisted of drag coefficients, front and rear lift coefficients, base and door surface pressures, and wake surveys at various planes around the wheels. Overall, a comprehensive set of validation data was taken. The CFD simulations were transient, and the geometry closely replicated the experimental geometry, including the tires' deformations. Generally, the MRFg method predicted the effects of the various tread patterns on the drag coefficient to within four counts. Some outliers occurred. The MRFg method predicted some of the flowfield trends and magnitudes very well, but not others. The inclusion of the wind tunnel geometry significantly increased the accuracy of the methodology.
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| 3. |
- Bonitz, Sabine, 1985, et al.
(författare)
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Experimental Investigation of the Near Wall Flow Downstream of a Passenger Car Wheel Arch
- 2018
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 11:1, s. 22-34
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Tidskriftsartikel (refereegranskat)abstract
- The flow around and downstream of the front wheels of passenger cars is highly complex and characterized by flow structure interactions between the external flow, fluid exiting through the wheelhouse, flow from the engine bay and the underbody. In the present paper the near wall flow downstream of the front wheel house is analyzed, combining two traditional methods. A tuft visualization method is used to obtain the limiting streamline pattern and information about the near wall flow direction. Additionally, time resolved surface pressure measurements are used to study the pressure distribution and the standard deviation. The propagation of the occurring flow structures is investigated by cross correlations of the pressure signal and a spectral analysis provides the characteristic frequencies of the investigated flow. It is found that two main flow phenomena can be observed: one originates from flow exiting the upper wheelhouse and a second one resulting from a separation on the lower wheel house edge. The frequency spectrum reveals a dominant Strouhal number of 0.2. As the observed flow structures are attributed to the wheel-wheelhouse interaction, a closed wheelhouse configuration is also investigated and the results confirm that the fluctuations and observed flow structures are created by the flow interaction between the wheel, wheelhouse and the rotation of the wheel.
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| 4. |
- Bonitz, Sabine, 1985, et al.
(författare)
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Structures of Flow Separation on a Passenger Car
- 2015
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 8:1, s. 177-185
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Tidskriftsartikel (refereegranskat)abstract
- The phenomenon of three-dimensional flow separation is and has been in the focus of many researchers. An improved understanding of the physics and the driving forces is desired to be able to improve numerical simulations and to minimize aerodynamic drag over bluff bodies. To investigate the sources of separation one wants to understand what happens at the surface when the flow starts to detach and the upwelling of the streamlines becomes strong. This observation of a flow leaving the surface could be captured by investigating the limiting streamlines and surface parameters as pressure, vorticity or the shear stress. In this paper, numerical methods are used to investigate the surface pressure and flow patterns on a sedan passenger vehicle. Observed limiting streamlines are compared to the pressure distribution and their correlation is shown. For this investigation the region behind the antenna and behind the wheel arch, are pointed out and studied in detail. Besides the discussion of the correlation between limiting streamlines and the surface pressure distribution, it is discussed how the surface pressure and limiting streamline development is formed. It is shown how vortices emanating from the antenna influence the surface pressure and therefore the limiting streamline pattern. Behind the front wheel arch it is explained how the separation bubble upstream influences the development of the limiting streamlines further downstream.
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| 5. |
- Elnady, Tamer, et al.
(författare)
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Investigation of the Acoustic Performance of After Treatment Devices
- 2011
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 4:2, s. 1068-1075
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Tidskriftsartikel (refereegranskat)abstract
- Diesel engines produce harmful exhaust emissions and high exhaust noise levels. One way of mitigating both exhaust emissions and noise is via the use of after treatment devices such as Catalytic Converters (CC), Selective Catalytic Reducers (SCR), Diesel Oxidation Catalysts (DOC), and Diesel Particulate Filters (DPF). The objective of this investigation is to characterize and simulate the acoustic performance of different types of filters so that maximum benefit can be achieved. A number of after treatment device configurations for trucks were selected and measured. A measurement campaign was conducted to characterize the two-port transfer matrix of these devices. The simulation was performed using the two-port theory where the two-port models are limited to the plane wave range in the filter cavity. These models are implemented in SIDLAB Software for the simulation of low frequency sound propagation in ducts, and SIDLAB was used to predict the transfer matrix of the tested configurations. This paper presents guidelines for dividing these complicated systems into a number of simple 1D elements. Specifically, strategies for modeling the side inlet and outlet end caps are documented. The model takes about 15 minutes to set-up and 15 seconds to solve which demonstrates the power of using two-port techniques in modeling exhaust systems. The comparisons show good agreement between the measured and simulated transmission loss in the plane wave region.
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| 6. |
- Elnady, T., et al.
(författare)
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Systematic Optimization of an Exhaust System to Meet Noise Radiation Criteria at Idle
- 2014
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 7:3
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Tidskriftsartikel (refereegranskat)abstract
- Exhaust noise is a major contributor to the radiated noise level of a vehicle, especially at idle. The radiated noise level has to meet a certain criteria based on regulation and consumer demand. In many cases, the problem appears after the vehicle is manufactured and the tailpipe noise measurement is performed indicating a high noise level that needs to be reduced. This paper describes one of those cases where the radiated noise level of a certain passenger car at idle was required to be reduced by 6 dB(A). The exhaust system consists of one main muffler and one auxiliary muffler. A 1D two-port model of the exhaust system including the two mufflers was built using commercial software. This model was validated against the measurement of the two-port matrix of both mufflers. The model was then used together with tailpipe noise measurements to estimate the characteristics of the source strength and impedance. Using a 1D model of the complete system, it was possible to propose several modifications for the vehicle manufacturer to choose from. A systematic optimization approach is presented in this paper describing several suggestions to reduce the radiated tailpipe noise.
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| 7. |
- He, Yuping, et al.
(författare)
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An Integrated Design Method for Articulated Heavy Vehicles with Active Trailer Steering Systems
- 2010
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 3:1, s. 158-174
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an integrated design method for active trailer steering (ATS) systems of articulated heavy vehicles (AHVs). Of all contradictory design goals of AHVs, two of them, i.e. path-following at low speeds and lateral stability at high speeds, may be the most fundamental and important, which have been bothering vehicle designers and researchers. To tackle this problem, a new design synthesis approach is proposed: with design optimization techniques, the active design variables of ATS systems and passive design variables of trailers can be optimized simultaneously; the ATS controller derived from this approach has two operational modes, one for improving lateral stability at high speeds and the other for enhancing path-following at low speeds. To demonstrate the effectiveness of the proposed approach, it is applied to the design of an ATS system for an AHV with a tractor and a full trailer. Simulation results illustrate that compared with the baseline vehicle, the one derived from the design synthesis approach decreases low-speed off-tracking by 35.2% and reduces high-speed rearward amplification ratio by 30.0%. The proposed approach may be used for identifying desired design variables and predicting performance envelopes in the early design stages of AHVs with ATS systems.
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| 8. |
- Hobeika, Teddy, 1988, et al.
(författare)
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Force Based Measurement Method for Cooling Flow Quantification
- 2017
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 10:2, s. 619-627
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Tidskriftsartikel (refereegranskat)abstract
- AbstractQuantification of heat exchanger performance in its operative environment is in many engineering applications an essential task, and the air flow rate through the heat exchanger core is an important optimizing parameter. This paper explores an alternative method for quantifying the air flow rate through compact heat exchangers positioned in the underhood of a passenger car. Unlike conventional methods, typically relying on measurements of direct flow characteristics at discrete probe locations, the proposed method is based on the use of load-cells for direct measurement of the total force acting on the heat exchanger. The air flow rate is then calculated from the force measurement. A direct comparison with a conventional pressure based method is presented as both methods are applied on a passenger car’s radiator tested in a full scale wind tunnel using six different grill configurations. The measured air flow rates are presented and discussed over a wide range of test velocities. The advantages and draw backs of both approaches are compared and discussed in detail. The proposed method is non-intrusive, leaving the heat exchanger core intact, with no need for integration of measurement points over the core region. Due to the measuring principle, the load-cell method will inherently over-predict the air-flow rate. This error is quantified and an empirical correction function is investigated. This paper shows that the corrected force based method determines the air flow rate through a heat exchanger with an accuracy similar to that of traditional pressure/velocity methods while offering a considerable number of advantages.
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| 9. |
- Hobeika, Teddy, 1988, et al.
(författare)
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Investigation of the Influence of Tyre Geometry on the Aerodynamics of Passenger Cars
- 2013
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 6:1, s. 316-325
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that wheels are responsible for a significant amount of the total aerodynamic drag of passenger vehicles. Tyres, and mostly rims, have been the subject of research in the automotive industry for the past years, but their effect and interaction with each other and with the car exterior is still not completely understood. This paper focuses on the use of CFD to study the effects of tyre geometry (tyre profile and tyre tread) on road vehicle aerodynamics. Whenever possible, results of the numerical computations are compared with experiments.More than sixty configurations were simulated. These simulations combined different tyre profiles, treads, rim designs and spoke orientation on two car types: a sedan and a sports wagon. Two tyre geometries were obtained directly from the tyre manufacturer, while a third geometry was obtained from our database and represents a generic tyre which covers different profiles of a given tyre size. All geometries were deformed based on measured wind tunnel data under a defined load and rotating conditions of 100 kph.Results have shown that the main grooves consistently lead to a decrease of both drag and lift. The edge pattern however, did not show a clear trend for drag and lift with respect to the different configurations studied, although its influence was always more noticeable on the sports wagon. The larger profile of the generic tyre resulted in higher drag and lift values with relation to the tyres obtained from the manufacturer. For a given rim, a drag difference was observed between two tyre geometries with same profile but different tyre tread. These findings lead to the conclusion that tyre profile, as well as tyre pattern, are important to consider. These results were confirmed by wind tunnel tests. In conclusion, the work of aerodynamic optimization of rims cannot be separated from the tyre itself.
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| 10. |
- Hobeika, Teddy, 1988, et al.
(författare)
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Tyre Pattern Features and their Effects on Passenger Vehicle Drag
- 2018
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Ingår i: SAE International Journal of Passenger Cars - Mechanical Systems. - : SAE International. - 1946-3995 .- 1946-4002. ; 11:5, s. 401-413
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Tidskriftsartikel (refereegranskat)abstract
- In light of the drive for energy efficiency and low CO 2 emissions, extensive research is performed to reduce vehicle aerodynamic drag. The wheels are relatively shielded from the main flow compared to the exterior of the passenger car, however, they are typically responsible for around 25% of the overall vehicle drag. This contribution is large as the wheels and tyres protrude into the flow and change the flow structure around the vehicle underbody. Given that the tyre is the first part of the wheel to get in contact with the oncoming flow, its shape and features have a significant impact on the flow pattern that develops. This study aims at identifying the general effects of two main tyre features, the longitudinal rain grooves and lateral pattern grooves, using both CFD and wind tunnel tests. This is performed by cutting generic representations of these details into identical slick tyres. Combinations of the two resulted in four physical tyre patterns that are tested on both a production and a closed rim. The test setup is reproduced in CFD taking the tyre deformation under loading into account. Due to the tyre's deformation, Moving Reference Frame - grooves (MRFg) was used to model rotation, while the rim spokes were modelled with the sliding mesh approach. The results indicate that the rain grooves play a significant role in reducing drag when introduced on a slick tyre both in test and simulations, while the results from adding lateral grooves were less consistent dependent on the rim-tyre combination. The interaction between the longitudinal and lateral grooves could be observed on the overall vehicle drag. In general, CFD is able to predict the drag changes for different tyre patterns with good accuracy for the open rim, however the closed rim case proved to be more challenging.
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