Simultaneous Improvement of Vehicle Under-Hood Airflow and Cooling Drag Using 3D CFD Simulation

Zhang, Chunhui; Uddin, Mesbah; Xu, Song; Chen, Fu; Foster, Lee

doi:10.4271/2016-01-0200

Cited by 12 publications

(10 citation statements)

References 23 publications

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“…The combination of air-duct, inclined CRFM, and side grille opening sealing were investigated to achieve a simultaneous improvement of the radiator performance and cooling drag reduction. The benefits of such design changes have been well demonstrated by the authors in a previous study [42].…”

Section: Cases Investigatedmentioning

confidence: 67%

Turbulence Modeling Effects on the CFD Predictions of Flow over a Detailed Full-Scale Sedan Vehicle

Zhang

Bounds

Foster³

et al. 2019

Fluids

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In today’s road vehicle design processes, Computational Fluid Dynamics (CFD) has emerged as one of the major investigative tools for aerodynamics analyses. The age-old CFD methodology based on the Reynolds Averaged Navier–Stokes (RANS) approach is still considered as the most popular turbulence modeling approach in automotive industries due to its acceptable accuracy and affordable computational cost for predicting flows involving complex geometries. This popular use of RANS still persists in spite of the well-known fact that, for automotive flows, RANS turbulence models often fail to characterize the associated flow-field properly. It is even true that more often, the RANS approach fails to predict correct integral aerodynamic quantities like lift, drag, or moment coefficients, and as such, they are used to assess the relative magnitude and direction of a trend. Moreover, even for such purposes, notable disagreements generally exist between results predicted by different RANS models. Thanks to fast advances in computer technology, increasing popularity has been seen in the use of the hybrid Detached Eddy Simulation (DES), which blends the RANS approach with Large Eddy Simulation (LES). The DES methodology demonstrated a high potential of being more accurate and informative than the RANS approaches. Whilst evaluations of RANS and DES models on various applications are abundant in the literature, such evaluations on full-car models are relatively fewer. In this study, four RANS models that are widely used in engineering applications, i.e., the realizable k - ε two-layer, Abe–Kondoh–Nagano (AKN) k - ε low-Reynolds, SST k - ω , and V2F are evaluated on a full-scale passenger vehicle with two different front-end configurations. In addition, both cases are run with two DES models to assess the differences between the flow predictions obtained using RANS and DES.

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Section: Cases Investigatedmentioning

confidence: 67%

Turbulence Modeling Effects on the CFD Predictions of Flow over a Detailed Full-Scale Sedan Vehicle

Zhang

Bounds

Foster³

et al. 2019

Fluids

Self Cite

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“…Current cooling air flow CFD studies can be traced to work undertaken on generic models such as the Ahmed body, modified with an internal duct, as performed by Barnard [1,2]. More recent work in the field has taken advantage of modern computational resources in modeling full vehicle airflow problems on production automotive geometries such as Large Saloons [3,4,5] and SUVs [3,6,7,8,9].…”

Section: Cooling Air Flowsmentioning

confidence: 99%

“…[10,11,12,13]. Other relevant work in this subject has focused on studying the effect of various components on the system [5,9,14].…”

Section: Cooling Air Flowsmentioning

confidence: 99%

Complete Body Aerodynamic Study of three Vehicles

Simmonds¹,

Pitman²,

Tsoutsanis³

et al. 2017

SAE Technical Paper Series

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Cooling drag, typically known as the difference in drag coefficient between open and closed cooling configurations, has traditionally proven to be a difficult flow phenomenon to predict using computational fluid dynamics. It was seen as an academic yardstick before the advent of grille shutter systems. However, their introduction has increased the need to accurately predict the drag of a vehicle in a variety of different cooling configurations during vehicle development. This currently represents one of the greatest predictive challenges to the automotive industry due to being the net effect of many flow field changes around the vehicle. A comprehensive study is presented in the paper to discuss the notion of defining cooling drag as a number and to explore its effect on three automotive models with different cooling drag deltas using the commercial CFD solvers; STARCCM+ and Exa PowerFLOW. The notchback DrivAer model with under-hood cooling provides a popular academic benchmark alongside two fully-engineered production cars; a large saloon (Jaguar XJ) and an SUV (Land Rover Range Rover). Initially three levels of spatial discretization were used with three steady-state RANS solvers (k-ɛ realizable, k-ω SST and Spalart-Allmaras) to ascertain whether previous work using RANS on the large saloon studying cooling flows could be replicated on other vehicle shapes. For both the full-production vehicles, all three turbulence models were capable of predicting the cooling drag delta within 5 counts (0.005 C d). However, the DrivAer model was much more sensitive to both changes in turbulence models and mesh sizes. For the SA turbulence model only the drag coefficient was well predicted, for the other two RANS models no amount of grid refinement allowed the models to correctly predict the flow field. It was seen when comparing the k-ɛ realizable and SA turbulence models the difference in cooling drag was attributed to the rear of the vehicle. This highlighted that despite similar drag values from the cooling package, the cooling deltas were very different, suggesting that cooling drag cannot be thought of as open-closed drag with the addition of drag due to the cooling package. Further work on the DrivAer model expanded on the RANS simulations utilizing the eddy-resolving methods, IDDES and LBM, as validation cases. Oscillations which were seen in the SA and k-ω SST RANS turbulence models were shown to be of similar levels to those in the transient methods indicating a pseudo-unsteadiness present in the steady-state solvers and the importance of resolving it. Drag and lift coefficient absolute values were compared showing that only the IDDES method with sliding wheels and LBM method could obtain physical results for the majority of the tested criteria.

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“…On the other hand, Nouzawa, et al, considered the engine cooling air in the system of a real vehicle consisting of: 1) flow around the front-end shape; 2) flow between the grille and the radiator; and 3) flow within the engine compartment and scavenging, with experimental analysis [7]. Recently numerical simulation on the cooling drag has been carried out in the system as each real vehicle [8] [9] [10]. In addition, with regard to the engine-compartment aerodynamics, other than documentations about drag and cooling efficiency, there are few publications about the running stability such as reduction of lift and about the side-wind stability, and therefore further research will be necessary.…”

Section: Introductionmentioning

confidence: 99%

Reduction of Aerodynamically Undesirable Influences Due to Engine Cooling Flow in Road Vehicle

Sawaguchi¹,

Takakura²

2020

JFCMV

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The purpose of this research is to clarify causes for the change in aerodynamic characteristics of a road vehicle model due to engine cooling flow in wind-tunnel experiments with the moving-belt ground board, in order to propose methods to reduce the drag and lift. With regard to engine cooling flow, the air-intake system was adjusted with variable opening area and position for the engine loading system of FF and FR with and without a radiator. A simplified 1/5 scale vehicle model was manufactured with transparent externals around the engine for flow visualization. The overall results show that with enlargement of the opening area, the drag and the front lift increased and the rear lift decreased. The flow visualization and the measurements of underfloor velocity and surface pressure indicated the cause of the characteristics changes. Enlargement of the opening area causes flow disturbance by merging of the scavenging flow and the underfloor flow, which has blockage effects for the upstream of each flow with keeping high pressure in the engine compartment and causes pressure loss under the floor behind the engine unit. The difference between the two engine loading systems lies indirection and location of the engine unit, which causes the differences of how the flow features affect the aerodynamic characteristics. The effect of the radiator is to reduce the range of changes in drag and lift. Finally, it is discussed that the principle of reducing drag and lift is to suppress interference of scavenging flow, and concrete methods are proposed.

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Simultaneous Improvement of Vehicle Under-Hood Airflow and Cooling Drag Using 3D CFD Simulation

Cited by 12 publications

References 23 publications

Turbulence Modeling Effects on the CFD Predictions of Flow over a Detailed Full-Scale Sedan Vehicle

Turbulence Modeling Effects on the CFD Predictions of Flow over a Detailed Full-Scale Sedan Vehicle

Complete Body Aerodynamic Study of three Vehicles

Reduction of Aerodynamically Undesirable Influences Due to Engine Cooling Flow in Road Vehicle

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