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Vehicle Aerodynamics, 2018

2018-04-03
Vehicle aerodynamic development, drag reduction and fuel economy, handling and stability, cooling flows, surface soiling and water management, vehicle internal environment, tyre aerodynamics and modelling, aeroacoustics, structural response to aerodynamic loading, simulating the on-road environment, onset flow turbulence, unsteady aerodynamics, fundamental flow structures, new test methods and facilities, new applications of computational fluid dynamics simulation, competition vehicle aerodynamics.
Technical Paper

Guidelines on the Use of Experimental Sea for Modeling and Understanding Road Noise in Cars

1999-05-17
1999-01-1704
Over the last years, SEA has been recognized as a useful tool to model and analyze the high-frequency vibro-acoustic behavior of fully assembled complex structures. This paper discusses the experimental derivation of the loss factor model of a passenger car. The paper outlines the different steps which need to be taken to obtained a fully validated experimental SEA model. This includes the subdivision into subsystems, the PIM measurement campaign, the derivation of the loss factors and their associated confidence levels and the model validation. The paper further details how the experimental SEA model was used to quantify and investigate the airborne and structure-borne contributions to the interior noise level for a road noise test condition. The operational power inputs to the vehicle were indirectly determined from operational response measurements. A contribution analysis showed that airborne noise sources dominated structure-borne noise sources above 500Hz.
Technical Paper

Analysis of Vehicle Pillar Cavity Foam Block Effect on Interior Noise Using SEA

1999-05-17
1999-01-1701
Closed cell foam has been used for filling vehicle pillar cavities at select locations to block road noise transmitted through pillars. In the past, most pillar foam implementations in vehicle programs were driven by subjective improvements in interior sound. In this study road test results are used to correlate a detailed CAE (Computer-Aided Engineering) model based on the statistical energy analysis method. Noise reduction characteristics of pillar with a number of foam block fillings were then studied using the CAE model. The CAE models provided means to model and understand the mechanism of noise energy flow through pillar cavities. A number of insightful conclusions were obtained as result of the study.
Technical Paper

Evaluating Vehicle Interior Noise Quality Under Transient Driving Conditions

1999-05-17
1999-01-1683
This paper presents a software-driven procedure for continuous assessment facilitating an evaluation of non-stationary sound quality. The noise stimuli are presented to the test persons via headphones and a subwoofer from a personal computer. The key feature of the rating procedure is the “zonal pairwise comparison” for the time zones at the beginning and the end of the noise sequences. Evaluation of data together with time variant objective parameters by means of statistical methods is described. The results and models from multiple regession analysis are given.
Technical Paper

Quantification of Intake System Noise Using an Experimental Source-Transfer-Receiver Model

1999-05-17
1999-01-1659
Design optimisation with respect to interior noise is currently a topic of great concern for the automotive industry. An essential element in this process is to obtain a correct understanding of the various noise sources which are present, and the ways in which these sources propagate to the critical receiver. An experimental source-transfer-receiver methodology is presented, that allows quantifying the structure borne and airborne source strength of the intake system components and its contribution to the interior noise. The method allows interior noise optimisation after identification of the dominant contributors. The methodology is applied to identify the noise contribution of the air intake system to the interior noise of an 8-cylinder upper class vehicle. Correlation of the Structure Borne Transfer Path Analysis and Airborne Source Quantification models with physical decoupling experiments demonstrates a high correspondence.
Technical Paper

Intake/ Exhaust Noise Reduction with Rig Test Optimization – Case Studies

1999-05-17
1999-01-1660
The study employed the rig test method for the intake/exhaust noise investigation by using shaker. This article describes two case studies including 1.2 liter minivan and a 250 c.c. motorcycle. For the minivan case, it was verified that along with the reduction of 5∼8 dB(A) of intake noise the interior noise was also improved using the rig test optimization result. For the motorcycle case, It was found that there was very good correlation of the exhaust noise measured among the engine dynamometer, road test and rig test after the temperature effect was compensated. Hence, the study chose the rig test as a development tool to get prompt NVH evaluation results on the different exhaust pipe lengths and keep the development time schedule. From the results, it is concluded that the simple and cheap rig test evaluation technique is vital and a very effective tool to achieve the vehicle NVH development goal.
Technical Paper

Application of Computational Fluid Dynamics for Flow Force Optimization of a High Pressure Fuel Injector Spill Valve

1999-05-03
1999-01-1537
Development of Caterpillar Fuel Systems' MEUI-B injector has involved application of Computational Fluid Dynamics (CFD) in order to improve performance of the high pressure spill valve. Initial performance bench testing with concept stage experimental injectors indicated that the chamber pressure was decaying at an unacceptably slow rate, and the valve demonstrated erratic behavior at some operating conditions. The slow pressure decay and inconsistent spill valve motion were believed to be caused by flow forces generated during the low lift portion of the spill valve opening event. This theory was pursued by utilizing CFD to design two valves for testing in the next phase of the injector development cycle: A baseline geometry, similar to the original concept injector valve, and a new design incorporating localized seat geometry changes for inducing flow force assisted valve opening.
Technical Paper

Shoebox Converter Design for Thinwall Ceramic Substrates

1999-05-03
1999-01-1542
Shoebox catalytic converter design to securely mount thinwall substrates with uniform mounting mat Gap Bulk Density (GBD) around the substrate is developed and validated. Computational Fluid Dynamic (CFD) analysis, using heat transfer predictions with and without chemical reaction, allows to carefully select the mounting mat material for the targeted shell skin temperature. CFD analysis enables to design the converter inlet and outlet cones to obtain uniform exhaust gas flow to achieve maximum converter performance and reduce mat erosion. Finite Element Analysis (FEA) is used to design and optimize manufacturing tool geometry and control process. FEA gives insight to simulate the canning process using displacement control to identify and optimize the closing speed and load to achieve uniform mat Gap Bulk Density between the shell and the substrate.
Technical Paper

An Integrated Study of the Ford PRODIGY Aerodynamics using Computational Fluid Dynamics with Experimental Support

2000-04-02
2000-01-1578
The Ford P2000 prototype vehicle represents Ford Motor Company's commitment towards environmental stewardship through high fuel efficiency and low tailpipe emission. Low aerodynamic drag coefficient (Cd), weight reduction, and power train efficiency improvements are required in order to accomplish the overall fuel economy target. The objective of this study is to establish an aerodynamic efficient body shape (Cd = .20) that meets the cost, weight, styling, package and fuel economy targets. Furthermore, this vehicle must be able to be operated and manufactured. A new computational fluid dynamics (CFD) method based on a lattice gas approach was piloted for developing and evaluating body shape design alternatives in support of the P2000 PRODIGY aerodynamic objective. Wind tunnel tests were performed to further explore the aerodynamic opportunities that are beyond the capability of the computational method as well as validate the CFD prediction.
Technical Paper

Aerodynamics of the Bell P-39 Airacobra and P-63 Kingcobra

2000-05-09
2000-01-1678
This paper provides a retrospective of the aerodynamics of the Bell P-39 Airacobra and the Bell P-63 Kingcobra. Design details and information obtained from several drag reduction investigations conducted on these aircraft are presented. Additionally, results from a modern Computational Fluid Dynamics analysis of these aircraft are shown.
Technical Paper

Using CFD For Humidity Clearing Simulation of a Composite Headlamp

2000-04-02
2000-01-1598
The headlamp designs of today and the future will be increasingly complex to match the increasingly dramatic vehicle designs. These complex shapes require lamps that are vented to relieve pressure and thermal stresses. Specifying headlamp vent locations to optimize humidity clearing while minimizing dust intrusion is often a trial and error process requiring several iterations using prototypes. Computational Fluid Dynamics external flow simulations can provide an accurate view of the lamp external air flow and pressure gradients which allows the designer to specify vent locations for maximum air exchange. CFD can thus reduce the need for prototyping and testing while reducing cost.
Technical Paper

CFD Approach for Optimum Design of DI Combustion System in Small Versatile Diesel Engine

1999-09-28
1999-01-3261
The simulation techniques play important role on contemporary engine design. In this study, computer fluid dynamics approach (CFD) was focused to design the intake and combustion system of the direct injection diesel engine for versatile use. A practicality was stressed as much as an accuracy to correspond to designer and researcher's requirements, such as close relationship to the engine performance and short period of computation. The correlation of the trapping efficiency and the swirl ratio was mainly focused. A steady flow rig tests and engine operation data were combined to improve their quality mutually.
Technical Paper

An Assessment of a Stratified Scavenging Process Applied to a Loop Scavenged Two-Stroke Engine

1999-09-28
1999-01-3272
Stratified scavenging has been applied to two-stroke engines to improve fuel consumption and reduce exhaust emissions. To evaluation how this is achieved a stratified scavenging process was simulated using a three-gas single-cycle scavenging apparatus. The experiment simulated the fuel stream entering the rear transfer port of a five port cylinder and air streams entering the remaining ports. The scavenging efficiency and fuel trapping are calculated after the cycle by examining the cylinder contents. The design of the apparatus is particularly suited to investigating cylinder design changes during the prototype stage of engine development. A simulation of the stratified scavenging experiment using the Computational Fluid dynamics (CFD) code VECTIS, showed good correlation with measured results. The simulation provides a real insight into the cylinder flow behaviour of the separate fuel and air streams entering the cylinder.
Technical Paper

AVL SDIS Mk.II - Low Cost Automotive FI Applied to 2-Stroke Engines for Future CARB - Regulations

1999-09-28
1999-01-3285
The basic Semi-Direct-Injection System (SDIS) which is already in production for PWC and applied to small 2-wheeler engines features a low-pressure fuel injection system injecting through the rear scavenge port window in the cylinder symmetry plane onto the piston crown. The patented new SDIS Mk.II System [1] injects through an (additional) scavenge port window that is positioned above the scavenge ports and is controlled by a window in the piston skirt. This new arrangement allows longer injection duration and also other injector positions and directions. A CFD simulation by AVL's FIRE-CFD-code with moving piston and exhaust gas dynamics compares the different injector positions and directions for WOT and rated speed and for a part throttle low speed case. The SDIS Mk.II injection system consists of mass-produced automotive parts thus giving a low cost approach for present 2-stroke engines requiring only moderate engine modifications.
Technical Paper

Numerical Study of Fuel/Air Mixture Preparation in a GDI Engine

1999-10-25
1999-01-3657
Numerical simulations are performed to investigate the fuel/air mixing preparation in a gasoline direct injection (GDI) engine. A two-valve OHV engine with wedge combustion chamber is investigated since automobiles equipped with this type of engine are readily available in the U.S. market. Modifying and retrofitting these engines for GDI operation could become a viable scenario for some engine manufactures. A pressure-swirl injector and wide spacing injection layout are adapted to enhance mixture preparation. The primary interest is on preparing the mixture with adequate equivalence ratio at the spark plug under a wide range of engine operating conditions. Two different engine operating conditions are investigated with respect to engine speed and load. A modified version of the KIVA-3V multi-dimensional CFD code is used. The modified code includes the Linearized Instability Sheet Atomization (LISA) model to simulate the development of the hollow cone spray.
Technical Paper

Performance of Prototype High Pressure Swirl Injector Nozzles for Gasoline Direct Injection

1999-10-25
1999-01-3654
Prototype intermittent swirl-generating nozzles for gasoline direct injection application were fabricated by modifying MPI injector nozzles. Design parameters include geometric configuration of nozzle internal flow passage such as orifice diameter and length, needle geometry and swirler passage designs. Operating parameters are considered such as injection pressure, ambient pressure, injected fuel mass and duration of injector opening. Performances of the nozzles have been characterized in terms of static and transient flow rate, initial and overall spray angle, penetration, mean droplet diameter and drop size distribution. Computational fluid dynamic modeling of internal flow for the nozzles provided additional insight in addition to the experimental measurements. Sprays from the prototype nozzle used for measurement in this study exhibited the general features of swirl injection sprays.
Technical Paper

Light Truck Aerodynamic Simulations Using a Lattice Gas Based Simulation Technique

1999-11-15
1999-01-3756
Several studies have been conducted in an effort to bring Computational Fluid Dynamics (CFD) out of the research arena (5) and into the product design environment as a useful aerodynamic design tool. The focus of these studies has ranged from extremely simple shapes to more complex geometries representative of real vehicles. This paper presents the results of real vehicle applications in which CFD was used to predict the aerodynamic effect of proposed surface modifications. The simulation data was generated using a numerical method derived from lattice gas theory to evaluate the aerodynamic effect of surface modifications. The commercial software Powerflow was used to prepare the model, perform the simulation and post-process the results. These case studies were performed in parallel with real vehicle development programs. The depth of experimental comparison data was limited by traditional vehicle program timing and budget constraints.
Technical Paper

Correlating the Diesel Spray Behavior to Nozzle Design

1999-10-25
1999-01-3555
This paper studies the effect of nozzle geometry on the flow characteristics inside a diesel fuel injection nozzle and correlates to the subsequent atomization process under different operating conditions, using simple turbulent breakup model. Two kinds of nozzles, valve covered orifice (VCO) and mini-SAC nozzle, with various nozzle design parameters were studied. The internal flow inside the nozzle was simulated using 3-D computational fluid dynamics software with k-ε turbulence model. The flow field at the nozzle exit was characterized by two parameters: the fuel discharge coefficient Cd and the initial amplitude parameter amp0. The latter parameter represents the turbulence characteristics of the exit flow. The effects of nozzle geometry on the mean velocity and turbulent energy distribution of the exit flow were also studied. The characteristics of the exit flow were then incorporated into the spray model in KIVA-II to study the effect of nozzle design on diesel spray behavior.
Technical Paper

Torque Converter Analytical Program for Blade Design Process

2000-03-06
2000-01-1145
In this paper, an integrated torque converter design process is described which improves converter performance while reduces the design cycle time and number of hardware iterations. The process utilizes a suite of tools to achieve the objectives. For quick and flexible geometry layout, the TORUS DESIGN TOOL is employed to create the underlying 2D-torus geometry with given packaging constraints. The BLADE DESIGN TOOL is subsequently used to generate 3D sheet-metal type profiles for the impeller, turbine, and reactor blades. The tool is equipped with a parametric capability for blade curvature and blade angle control to meet the performance requirements. The AIRFOIL DESIGN TOOL utilizes a sophisticated, parameterized algorithm to generate the desired airfoil shape around the reactor camber-line for improved performance.
Technical Paper

Development of a Closed Loop, Full Scale Automotive Climatic Wind Tunnel

2000-03-06
2000-01-1375
A closed loop full-scale automotive climatic wind tunnel is described. The tunnel simulates wind and rain as well as several road conditions. It generates under controlled heat loading, wind speeds of up to 50kmh with different approach boundary conditions, rains from drizzle to cloudburst and road inclines up to 15° in any direction. The design and optimization process of the tunnel functions is outlined and examples of its use in vehicle development are given. The size constraint and the need for a compact design are important features of the tunnel. The tunnel provides an important test bed for close scrutiny of the relationship between rain ingress, vehicle speed, road condition, heat loading and vehicle geometry. The tunnel can also be used to study vehicle thermal management, vehicle thermal comfort, engine cold starting, and wipers efficiency in sever cold weather.
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