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Technical Paper

Measurement of Exterior Surface Pressures and Interior Cabin Noise in Response to Vehicle Form Changes

2011-05-17
2011-01-1618
Automotive manufactures demand early assessment of vehicle form design against wind noise attribute to eliminate any engineering waste induced by late design changes. To achieve such an assessment, it is necessary to determine a measurable quantity which is able to represent vehicle form changes, and to understand the relationship between the quantity and vehicle interior cabin noise. This paper reports experimental measurements of vehicle exterior surface pressure and the interior cabin noise level in response to the change of exterior rear view mirror shape. Measurements show that exterior surface pressure on vehicle greenhouse panel is a primary factor of wind noise load to the interior cabin noise; they can be used in preliminary wind noise ranking. Care should be taken when using them in ranking vehicle form wind noise performance. It has been observed that a change in surface pressure on the front side window does not necessarily lead to a change in the interior cabin noise.
Technical Paper

PIV Analysis Comparing Flow Past NASCAR COT Rear Wing and Spoiler Traveling Forward and Backwards

2011-04-12
2011-01-1432
There have been claims that the rear wing on the NASCAR Car of Tomorrow (COT) race car causes lift in the condition where the car spins during a crash and is traveling backwards down the track at high speed [1,2]. When enough lift is generated, the race car can lose control and even become airborne. At least in part, to address this concern, a new rear spoiler was designed by NASCAR to replace the wing and prevent this dangerous condition. This paper looks at the flow characteristics of both the rear wing and the new spoiler using particle image velocimetry (PIV) to provide qualitative analysis as well as flow visualization. In particular, the interaction of these downforce devices with "roof flaps" (which are designed to prevent lift) is explored. These experiments are done in a continuous flow water tunnel having a cross section of 1.0 m2 using a simplified 10% scale model COT body with either a wing or spoiler attached.
Journal Article

Aerodynamic Investigation on the Effect of Varying Through-Hub Flow on a Formula One Front Wheel Assembly

2011-04-12
2011-01-1431
For open wheel race cars the front wheel flow and the interaction of its wake with downstream components is of significant importance. Considerable effort goes into the design of front wing end plates, barge boards and underfloor components in order to manage the front wheel flow. In this study a 50% scale Formula One front wheel assembly has been tested in the Durham University 2m₂ open jet wind tunnel to evaluate the effect of through-hub flow on its cooling drag and flow structures. Varying the amount of through-hub flow gave rise to a negative cooling drag trend whereby increasing the flow through the hub resulted in a decrease in drag. This observation has been explained both qualitatively and quantitatively by inlet spillage drag. Lower than optimum airflows through the brake scoop result in undesirable separation at the inside edge and hence, an increase in drag (reversing the cooling drag trend).
Technical Paper

An Investigation of Different Combustion Chamber Configuration, Intake Temperature, and Coolant Temperature in a HCCI Optical Engine

2011-08-30
2011-01-1765
The influence of different combustion chamber configuration, intake temperature, and coolant temperature on HCCI combustion processes were investigated in a single-cylinder optical engine. Two-dimensional images of the chemiluminescence were captured using an intensified CCD camera in order to understand the spatial distribution of the combustion. N-heptane was used as the test fuel. Three combustion chamber geometries with different squish lip, salient, orthogonal, reentrant shape, referred as V-type, H-type, and A-type respectively, were used in this study. Intake temperature was set to 65°C and 95°C, while coolant temperature was set to 85°C. The experimental data consisting of the in-cylinder pressure, heat release rate, chemiluminescence images all indicated that the different combustion chamber geometries result in different turbulence intensity in the combustion chamber, and thus affect the auto-ignition timing, chemiluminescence intensity, and combustion processes.
Technical Paper

SEA Wind Noise Load Case for Ranking Vehicle Form Changes

2011-05-17
2011-01-1707
Vehicle manufacturers demand early design assessment of vehicle wind noise attribute so as to eliminate engineering waste induced by late design changes. Vehicle wind noise attribute can be simulated with a Statistical Energy Analysis (SEA) model using exterior surface turbulence pressure on the vehicle greenhouse panel as the wind noise load. One important application of SEA wind noise model is the wind noise assessment for vehicle form design. Vehicle form optimization for wind noise plays an important role in lightweight vehicle architecture, since that reduction in the wind noise load will compensate the loss of vehicle body acoustic attenuation caused by down-gauge glazing and body panels. In this paper, two SEA wind noise load cases currently used in vehicle SEA wind noise modeling have been analyzed and evaluated against vehicle measurements.
Technical Paper

Analysis of Numerical Simulation on Reducing Drag of Van Body Truck

2011-09-13
2011-01-2286
With the crisis of energy becoming more severity, the research of cutting down the drag of commercial vehicles is more and more important. In this work, to reduce the drag of a van body truck, aerodynamic drag reduction designs are carried out by the method of numerical simulation. Plates are fixed on the aft-body with different angle of declination. The effects of reducing drag are studied and the mechanism is discussed. The paper selects four rear add-on devices with different obliquity by 5deg, 10deg, 15deg and 20deg. Seen from the results of numerical simulation, the rear add-on device can reduce the drag effectively. The CFD simulations indicate that addition of the flat plates reduces the drag about 5∼8%. When the declination angle is 15deg, the effect is the best and the drag of the truck model is reduced by 8.9% comparing with the configuration without add-on device. This work can offer important references for the optimize design of van body truck.
Journal Article

Drag Reduction of a Modern Straight Truck

2011-09-13
2011-01-2283
A wind tunnel test program was conducted at the Langley Full Scale Tunnel (LFST) to evaluate the performance of five passive drag reduction configurations on a modern straight truck at full scale. Configurations were tested in a build-up fashion with results representing a cumulative effect. Tested configurations include a front valance, a front box fairing, a boat-tail, an ideal side-skirt, and a practical side-skirt. Configurations were evaluated over a nominal 9 degree yaw sweep to establish wind averaged drag coefficients using SAE J1252. Genuine replicate yaw sweeps were used in an uncertainty analysis. Results show up to 28% improvement in wind-averaged drag coefficient and that significant gains can be made in straight truck fuel economy, even at non-highway speeds.
Technical Paper

Aerodynamic Effects of Roof Deflector and Cab Side Extenders for Truck-Trailer Combinations

2011-09-13
2011-01-2284
Today there are a large variety of drag-reducing devices for heavy trucks that are commonly used, for example, roof deflectors, cab side extenders and chassis fairings. These devices are often proven to be efficient, reducing the total aerodynamic resistance for the vehicle. However, the drag-reducing devices are usually identical for a specific pulling vehicle, independent of the layout of the vehicle combination. In this study, three vehicle combinations were analyzed. The total length of the vehicles varied between 10.10 m and 25.25 m. The combinations consisted of a rigid truck in combination with one or two cargo units. The size of the gap between the cargo units differed between the vehicle combinations. There were also three configurations of each vehicle combination with different combinations of roof deflector and cab side extenders, yielding a total number of nine configurations.
Journal Article

Spray Pattern Optimization for the Duratec 3.5L EcoBoost Engine

2009-06-15
2009-01-1916
A systematic methodology has been employed to develop the Duratec 3.5L EcoBoost combustion system, with focus on the optimization of the combustion system including injector spray pattern, intake port design, piston geometry, cylinder head geometry. The development methodology was led by CFD (Computational Fluid Dynamics) modeling together with a testing program that uses optical, single-cylinder, and multi-cylinder engines. The current study shows the effect of several spray patterns on air-fuel mixing, in-cylinder flow development, surface wetting, and turbulence intensity. A few sets of injector spray patterns are studied; some that have a wide total cone angle, some that have a narrow cone angle and a couple of optimized injector spray patterns. The effect of the spray pattern at part load, full load and cold start operation was investigated and the methodology for choosing an optimized injector is presented.
Technical Paper

Advances in Variable Density Wall Functions for Turbulent Flow CFD-Simulations, Emphasis on Heat Transfer

2009-06-15
2009-01-1975
A new variable density / physical property wall function formalism has been developed. The new formalism is designed to extend the validity range of wall functions to cover both the low- and high-Reynolds-number domains so that the restrictions on the non-dimensional near-wall mesh resolution can be avoided. The new formalism also accounts for the temperature gradient induced variations of density, viscosity, heat conductivity and specific heat capacity. The new wall function formalism is constructed in conjunction with a modified low-Reynolds-number turbulence model in order to avoid the conflicting requirements of low- and high-Reynolds-number models on the near wall mesh resolution. The new formulation is validated with test simulations of strongly heated air flows in circular tube against measurements and Direct Numerical Simulation (DNS) results.
Journal Article

Numerical Investigation of Non-Reacting and Reacting Diesel Sprays in Constant-Volume Vessels

2009-06-15
2009-01-1971
A numerical investigation on a series of Diesel spray experiments in constant-volume vessels is proposed. Non reacting conditions were used to assess the spray models and to determine the grid size required to correctly predict the fuel-air mixture formation process. To this end, not only computed liquid and vapor penetrations were compared with experimental data, but also a detailed comparison between computed and experimental mixture fraction distributions was performed at different distances from the injector. Grid dependency was reduced by introducing an Adaptive Local Mesh Refinement technique (ALMR) with an arbitrary level of refinement. Once the capabilities of the current implemented spray models have been assessed, reacting conditions at different ambient densities and temperatures were considered. A Perfectly Stirred Reactor (PSR) combustion model, based on a direct integration of complex chemistry mechanisms over a homogenous cell, was adopted.
Technical Paper

Scattering Matrix Evaluation with CFD in Low Mach Number Flow Ducts

2009-05-19
2009-01-2040
We present an efficient methodology to perform calculations of acoustic propagation and scattering by components in ducts with flows. In this paper a methodology with a linearized Navier-Stokes equations solver in frequency domain is evaluated on a two-dimensional geometry of an in-duct area expansion. The Navier-Stokes equations are linearized around a time-independent mean flow that is obtained from an incompressible Reynolds Averaged Navier-Stokes solver which uses a k-ε turbulence model and adaptive mesh refinement. A plane wave decomposition method based on acoustic pressure and velocity is used to extract the up and downstream propagating waves. The reflection of the acoustic waves by the induct area expansion is calculated and compared to both measurements and analytical models. Frequencies in the plane wave range up to the cut-on frequency of the first higher order propagating acoustical mode are considered.
Technical Paper

Simulation of Scavenging Process, Internal Mixture Preparation, and Combustion of a Gasoline Direct Injection Two-Cylinder Two-Stroke Engine

2009-11-03
2009-32-0046
The continuous improvement of the numerical methods together with the increase of computer power allows the simulation of more and more complex technical problems even for increasing calculation domains. In order to get effective and significant results for the two-stroke two-cylinder engine, the simulation of the complete geometry with both cylinders and the complete exhaust port is required. However, the simulation requires several revolutions until the gas dynamic inside the exhaust port achieves a steady state. Hence, the simulation of a two-cylinder two-stroke engine consumes a lot of calculation time; nevertheless it is still acceptable in the development process of a new engine. This paper covers the discussion of the simulation of a two-stroke two-cylinder high-performance engine using the commercial CFD Code Fluent 6.3.26. The used settings for the simulation, like the turbulence model, injection settings, combustion model and reduced reaction mechanism are presented.
Technical Paper

Study on Similarity of Pumping Flow in Engine Crankcase

2009-11-03
2009-32-0051
For the prediction of pumping loss in the engine crankcase at the early stage of engine design, a similarity law of the pumping loss on parallel cylinders with the phase difference of 180 degrees has been derived from the sum of the power loss due to the drag force of airflow through the cylinder bulkhead holes and the inertia force of fluid. It has been found that the mean effective pressure in the crankcase is in proportion to the square of the mean flow velocity at the bulkhead holes. Then, in order to validate the similarity law, by using a prototype engine with inline four cylinders, the pumping loss was estimated by subtracting the frictional loss with special pistons that had air holes, from the power loss in which the area of the bulkhead holes and engine speed were changed. The experimental results of the pumping loss were normalized by the similarity law. As a consequence, it has been shown that the pumping loss obeys the law.
Technical Paper

Cooperative Steer Control on Motorcycle between Rider and Active Support Torque

2009-11-03
2009-32-0060
In this research, we aim at the construction of a steering cooperation-type front-wheel steering control system to reduce the rider's steering load by stabilizing the behavior of the motorcycle when turbulence in the direction of a roll occurs during low-speed driving. Finally, a front-wheel steering control system that considers cooperation with a rider's steering based on the experimental result is constructed, and the utility is verified by simulation.
Technical Paper

Exterior Styling of an Intercity Transport Bus for Improved Aerodynamic Performance

2009-12-13
2009-28-0060
In this work, an intercity bus has been redesigned with enhanced exterior styling, reduced aerodynamic drag and increased comfort for the passengers. Extensive product study and market study were carried out and aspirations and frustrations of commuters were recorded. An operating intercity bus was benchmarked and analyzed for styling, aerodynamic performance and comfort. Fluent, a commercial CFD code was used to evaluate the aerodynamic performance. Principles of product design were used to analyse the styling and comfort. The benchmarked high floor bus was redesigned with low - floor for reduced aerodynamic drag. The exterior was redesigned with emphasis on improvised aerodynamic performance and appealing looks. The interior was modified to meet aspirations of the commuters. The results of the redesigned exterior body showed a reduction of Cd from 0.53 to 0.29 and overall aerodynamic drag reduction by 60% due to combined effect of reduced Cd and frontal area.
Technical Paper

IMPROVEMENT OF PERFORMANCE AND EMISSION CHARACTERISTICS OF A DI DIESEL ENGINE WITH TURBULENCE INDUCED PISTON (INTERNAL JET PISTON) USING BIODIESEL BLENDS

2009-12-13
2009-28-0035
Biodiesel derived from vegetable oil are quite promising alternative fuels for diesel engines, because of their low environmental impact and has potential as an alternative fuel for diesel engine without any modification on the engine Use of vegetable oils in diesel engines leads to slightly inferior performance and higher smoke emissions due to their high viscosity. The performance of vegetable oils can be improved by modifying them through the transesterification process. In this study, an attempt is made to investigate the influence of turbulence inducement using internal jets in a Direct Injection (DI) diesel engine combustion chamber with diesel and palm oil methyl ester (POME). The turbulence in engine cylinder is induced by providing internal jets on the piston crown, located diametrically opposite on the piston crown. The working fluid has a tangential entry into the bowl through these holes.
Technical Paper

Kinematic Analysis of Multi-Axle Steering System for Articulated Vehicle

2009-01-21
2009-26-0067
Steering of non-driven axles of semi-trailer results in improvement of maneuverability during negotiating sharp turn and reduces tyre drag and wear by relieving locked-in forces in comparison to non-steered axles. Among few, command steering mechanism is reported to be most efficient method of steering of articulated vehicles. In this type, the axles of semi-trailer are steered in relation with the articulation of tractor. The articulation angle of tractor is sensed by an actuation mechanism integrated on trailer at fifth wheel location and transferred hydraulically to the steering linkages. Mathematical equations have been developed based on Ackerman's Principle to estimate theoretical steering angle when Tractor-Trailer negotiate any turn. Steering linkage geometry has been conceptualised, kinematically modelled and analysed by using ADAMS. Equations developed for theoretical steering angles are incorporated in ADAMS as run time functions.
Technical Paper

Numerical Investigations on Crosswind Aerodynamics and its Effect on the Stability of a Passenger Car

2009-01-21
2009-26-0059
In crosswind, or while passing another vehicle in still air, the flow around an automobile becomes asymmetric, thus altering the yawing moment, drag and lift. This paper discusses the details of crosswind aerodynamics of a typical sedan. The investigations, limited to numerical analysis, were carried out to predict the drag and lift coefficients, and the yaw moments on the selected car using a commercially available CFD software, FLUENT. The analysis was carried out for three car speeds, six crosswind angles and five crosswind velocities in various combinations. The results have shown that the drag coefficient initially decreases at 15° crosswind angle and then increases as the crosswind angle is increased. Further, the drag coefficient, lift coefficient and the yaw moment increase as the crosswind velocity increases. It is observed that the flow field around the car, especially at the rear, changes substantially with a change in the crosswind angle.
Technical Paper

The Lattice-Boltzmann-VLES Method for Automotive Fluid Dynamics Simulation, a Review

2009-01-21
2009-26-0057
The lattice Boltzmann (LB) method has been successfully used in conjunction with a Very Large-Eddy Simulation (VLES) turbulence modeling approach for over a decade for the accurate prediction of automotive fluid dynamics. Its success lies in the unique underlying physics that is significantly different from traditional computational fluid dynamics methods. In this paper, we provide a complete description of the method followed by a set of examples which show its use in the automotive industry. We will first provide a review of the physics and numerical methods. Here the LB method and its relationship to kinetic theory and the Navier-Stokes equations will be briefly discussed. We will summarize the strengths of LB method, especially for the solution of transient flows in extremely complex geometries. The VLES turbulence modeling method will be presented next, as well as how VLES neatly fits into the LB framework.
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