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Journal Article

1-D Simulation Study of Divided Exhaust Period for a Highly Downsized Turbocharged SI Engine - Scavenge Valve Optimization

2014-04-01
2014-01-1656
Fuel efficiency and torque performance are two major challenges for highly downsized turbocharged engines. However, the inherent characteristics of the turbocharged SI engine such as negative PMEP, knock sensitivity and poor transient performance significantly limit its maximum potential. Conventional ways of improving the problems above normally concentrate solely on the engine side or turbocharger side leaving the exhaust manifold in between ignored. This paper investigates this neglected area by highlighting a novel means of gas exchange process. Divided Exhaust Period (DEP) is an alternative way of accomplishing the gas exchange process in turbocharged engines. The DEP concept engine features two exhaust valves but with separated function. The blow-down valve acts like a traditional turbocharged exhaust valve to evacuate the first portion of the exhaust gas to the turbine.
Journal Article

A Computational Approach to Assess Buffeting and Broadband Noise Generated by a Vehicle Sunroof

2015-04-14
2015-01-1532
Car manufacturers put large efforts into reducing wind noise to improve the comfort level of their cars. Each component of the vehicle is designed to meet its individual noise target to ensure the wind noise passenger comfort level inside the vehicle is met. Sunroof designs are tested to meet low-frequency buffeting (also known as boom) targets and broadband noise targets for the fully open sunroof with deflector and for the sunroof in vent position. Experimentally testing designs and making changes to meet these design targets typically involves high cost prototypes, expensive wind tunnel sessions, and potentially late design changes. To reduce the associated costs as well as development times, there is strong motivation for the use of a reliable numerical prediction capability early in the vehicle design process.
Journal Article

A Computational Approach to Evaluate the Automotive Windscreen Wiper Placement Options Early in the Design Process

2013-05-13
2013-01-1933
For most car manufacturers, wind noise from the greenhouse region has become the dominant high frequency noise contributor at highway speeds. Addressing this wind noise issue using experimental procedures involves high cost prototypes, expensive wind tunnel sessions, and potentially late design changes. To reduce the associated costs as well as development times, there is strong motivation for the use of a reliable numerical prediction capability early in the vehicle design process. Previously, a computational approach that couples an unsteady computational fluid dynamics solver (based on a Lattice Boltzmann method) to a Statistical Energy Analysis (SEA) solver had been validated for predicting the noise contribution from the side mirrors. This paper presents the use of this computational approach to predict the vehicle interior noise from the windshield wipers, so that different wiper placement options can be evaluated early in the design process before the surface is frozen.
Journal Article

A Fully Coupled, 6 Degree-of-Freedom, Aerodynamic and Vehicle Handling Crosswind Simulation using the DrivAer Model

2016-04-05
2016-01-1601
In a real-world environment, a vehicle on the road is subjected to a range of flow yaw angles, the most severe of which can impact handling and stability. A fully coupled, six degrees-of-freedom CFD and vehicle handling simulation has modelled the complete closed loop system. Varying flow yaw angles are introduced via time dependent boundary conditions and aerodynamic loads predicted, whilst a handling model running simultaneously calculates the resulting vehicle response. Updates to the vehicle position and orientation within the CFD simulation are achieved using the overset grid method. Using this approach, a crosswind simulation that follows the parameters of ISO 12021:2010 (Sensitivity to lateral wind - Open-loop test method using wind generator input), was performed using the fastback variant of the DrivAer model. Fully coupled aerodynamic and vehicle response was compared to that obtained using the simplified quasi-steady and unsteady, one way coupled method.
Journal Article

A Parametric Study of Automotive Rear End Geometries on Rear Soiling

2017-03-28
2017-01-1511
The motivation for this paper is to consider the effect of rear end geometry on rear soiling using a representative generic SUV body. In particular the effect of varying the top slant angle is considered using both experiment and Computational Fluid Dynamics (CFD). Previous work has shown that slant angle has a significant effect on wake shape and drag and the work here extends this to investigate the effect on rear soiling. It is hoped that this work can provide an insight into the likely effect of such geometry changes on the soiling of similarly shaped road vehicles. To increase the generality of results, and to allow comparison with previously obtained aerodynamic data, a 25% scale generic SUV model is used in the Loughborough University Large Wind Tunnel. UV doped water is sprayed from a position located at the bottom of the left rear tyre to simulate the creation of spray from this tyre.
Journal Article

Analytical and Developmental Techniques Utilized in the Structural Optimization of a New Lightweight Diesel Engine

2015-06-15
2015-01-2298
Jaguar Land Rover (JLR) has designed and developed a new inline 4 cylinder engine family, branded Ingenium. In addition to delivering improved emissions and fuel economy over the outgoing engine, another key aim from the outset of the program was to reduce the combustion noise. This paper details the NVH development of the lead engine in this family, a 2.0 liter common rail turbo diesel. The task from the outset of this new program was to reduce the mass of the engine by 21.5 kg, whilst also improving the structural attenuation of the engine by 5 dB in comparison to the outgoing engine. Improving the structural attenuation by 5 dB was not only a key enabler in reducing combustion noise, but also helped to achieve a certified CO2 performance of 99 g/km in the all-new Jaguar XE model, by allowing more scope for increasing cylinder pressure forcing without compromising NVH.
Journal Article

Application of CFD to Predict Brake Disc Contamination in Wet Conditions

2016-04-05
2016-01-1619
Brake disc materials are being utilised that have low noise/dust properties, but are sensitive to contamination by surface water. This drives large dust shields, making brake cooling increasingly difficult. However, brake cooling must be delivered without compromising aerodynamic drag and hence CO2 emissions targets. Given that front brake discs sit in a region of geometric, packaging and flow complexity optimization of their performance requires the analysis of thermal, aerodynamic and multi-phase flows. Some of the difficulties inherent in this task would be alleviated if the complete analysis could be performed in the same CAE environment: utilizing common models and the same solver technology. Hence the project described in this paper has sought to develop a CFD method that predicts the amount of contamination (water) that reaches the front brake discs, using a standard commercial code already exploited for both brake disc thermal and aerodynamics analysis.
Technical Paper

Aspects of Numerical Modelling of Flash-Boiling Fuel Sprays

2015-09-06
2015-24-2463
Flash-boiling of sprays may occur when a superheated liquid is discharged into an ambient environment with lower pressure than its saturation pressure. Such conditions normally exist in direct-injection spark-ignition engines operating at low in-cylinder pressures and/or high fuel temperatures. The addition of novel high volatile additives/fuels may also promote flash-boiling. Fuel flashing plays a significant role in mixture formation by promoting faster breakup and higher fuel evaporation rates compared to non-flashing conditions. Therefore, fundamental understanding of the characteristics of flashing sprays is necessary for the development of more efficient mixture formation. The present computational work focuses on modelling flash-boiling of n-Pentane and iso-Octane sprays using a Lagrangian particle tracking technique.
Journal Article

Assessing the Aeroacoustic Response of a Vehicle to Transient Flow Conditions from the Perspective of a Vehicle Occupant

2014-04-01
2014-01-0591
On-road, a vehicle experiences unsteady flow conditions due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. Separated flow structures in the sideglass region of a vehicle are particularly sensitive to unsteadiness in the onset flow. These regions are also areas where strong aeroacoustic effects can exist, in a region close to the passengers of a vehicle. The resulting aeroacoustic response to unsteadiness can lead to fluctuations and modulation at frequencies that a passenger is particularly sensitive towards. Results presented by this paper combine on-road measurement campaigns using instrumented vehicles in a range of different wind environments and aeroacoustic wind tunnel tests.
Journal Article

Assessment of Broadband Noise Generated by a Vehicle Sunroof at Different Flow Conditions using a Digital Wind Tunnel

2015-06-15
2015-01-2321
For the automotive industry, the quality and level of the wind noise contribution has a growing importance and therefore should be addressed as early as possible in the development process. Each component of the vehicle is designed to meet its individual noise target to ensure the wind noise passenger comfort level inside the vehicle is met. Sunroof broadband noise is generated by the turbulent flow developed over the roof opening. A strong shear layer and vortices impacting on the trailing edge of the sunroof are typical mechanisms related to the noise production. Sunroof designs are tested to meet broadband noise targets. Experimentally testing designs and making changes to meet these design targets typically involves high cost prototypes, expensive wind tunnel sessions and potentially late design changes.
Technical Paper

Assessment of a Vehicle's Transient Aerodynamic Response

2012-04-16
2012-01-0449
A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, due to the unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. There is increasing concern about potential differences between the steady flow conditions used for development and the transient conditions that occur on the road. This paper seeks to determine if measurements made under steady state conditions can be used to predict the aerodynamic behaviour of a vehicle on road in a gusty environment. The project has included measurements in two full size wind tunnels, including using the Pininfarina TGS, steady-state and transient inlet simulations in Exa Powerflow, and a campaign of testing on-road and on-track. The particular focus of this paper is on steady wind tunnel measurements and on-road tests, representing the most established development environment and the environment experienced by the customer, respectively.
Journal Article

Base Pressure and Flow-Field Measurements on a Generic SUV Model

2015-04-14
2015-01-1546
The pressure on the base of a vehicle is a major contributor to the aerodynamic drag of all practical vehicle geometries, and for some vehicles, such as an SUV, it is particularly important because it can account for up to 50% of the overall drag. Understanding the mechanisms that influence the base pressure and developing our simulation tools to ensure that base pressure is accurately predicted are essential requirements for the vehicle design and engineering process. This paper reports an experimental study to investigate the base pressure on a specifically designed generic SUV model. The results from ¼ scale wind tunnel tests include force and moment data, surface pressures over the base region and particle image velocimetry (PIV) in the wake. Results are presented for the vehicle in different ride height, underfloor roughness and wheel configurations and the paper includes some description of the experimental errors. Some initial CFD simulations are also reported.
Technical Paper

CFD Simulation of Side Glass Surface Noise Spectra for a Bluff SUV

2006-04-03
2006-01-0137
Simulation of local flow structures in the A-pillar/side glass region of bluff SUV geometries, typical of Land Rover vehicles, presents a considerable challenge. Features such as relatively tight A-pillar radii and upright windscreens produce flows that are difficult to simulate. However, the usefulness of aerodynamics simulations in the early assessment of wind noise depends particularly on the local accuracy obtained in this region. This paper extends work previously published by the author(1) with additional data and analysis. An extended review of the relevant published literature is also provided. Then the degree to which a commercial Lattice-Boltzman solver (Exa PowerFLOW™) is currently able to capture both the local flow structure and surface pressure distribution (both time averaged and unsteady) is evaluated. Influential factors in the simulation are shown to be spatial resolution, turbulence and boundary layer modelling.
Journal Article

CFD-based Modelling of Flow Conditions Capable of Inducing Hood Flutter

2010-04-12
2010-01-1011
This paper presents a methodology for simulating Fluid Structure Interaction (FSI) for a typical vehicle bonnet (hood) under a range of onset flow conditions. The hood was chosen for this study, as it is one of the panels most prone to vibration; particularly given the trend to make vehicle panels lighter. Among the worst-case scenarios for inducing vibration is a panel being subjected to turbulent flow from vehicle wakes, and the sudden peak loads caused by emerging from a vehicle wake. This last case is typical of a passing manoeuvre, with the vehicle suddenly transitioning from being immersed in the wake of the leading vehicle, to being fully exposed to the free-stream flow. The transient flowfield was simulated for a range of onset flow conditions that could potentially be experienced on the open road, which may cause substantial vibration of susceptible vehicle panels.
Technical Paper

Complete Body Aerodynamic Study of three Vehicles

2017-03-28
2017-01-1529
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.
Journal Article

Development of a Virtual Multi-Axial Simulation Table to Enhance the Prognosis of Loads on Powertrain Mounting System During Durability Applications

2017-03-28
2017-01-0420
Vibration Isolation is the key objective of engine mounting systems in the automotive industry. A well-designed, robust engine mount must be capable of isolating the engine assembly from road-based excitations. Owing to high vibration inputs, engine mounts are susceptible to wear and failure. Thus, the durability of engine mounts is a cause for concern. A design validation methodology has been developed at Jaguar Land Rover using Multibody Dynamics (MBD) to enhance the prognosis of engine mount loads during full - vehicle durability test events. This paper describes the development of a virtual multi-axial simulation table rig (MAST Rig) to test virtual engine mount designs. For the particular example considered in this paper, a simple sinusoidal input is applied to the MAST Rig. The development of the virtual MAST Rig has been described including details of the modelling methodology.
Technical Paper

Effects of Charging System Variability on the Performance and Fuel Economy of a Supercharged Spark-Ignition Engine

2015-04-14
2015-01-1286
The paper discusses the effects of various charging system technologies on the performance and fuel consumption of a modern supercharged engine, the Jaguar Land Rover AJ126 3.0 litre V6. The goal of the project was to improve performance and reduce the fuel consumption of the standard engine by researching new technologies around the supercharger. As standard the AJ126 engine uses an Eaton R1320 supercharger with a fixed ratio drive from the crankshaft and no clutch.
Technical Paper

Engine Test Data Quality Requirements for Model Based Calibration: A Testing and Development Efficiency Opportunity

2013-04-08
2013-01-0351
This paper documents some of the findings from a joint JLR and AVL project which was conducted at the JLR Gaydon test facility in the UK. A testing and development efficiency concept is presented and test data quality is identified as a key factor. In support of this methods are proposed to correctly measure and set targets for data quality with high confidence. An illustrative example is presented involving a Diesel passenger car calibration process which requires response surface models (RSMs) of key engine measured quantities e.g. engine-out emissions and fuel consumption. Methods are proposed that attempt to quantify the relationships between RSM statistical model quality metrics, test data variability measures and design of experiment (DOE) formulation. The methods are tested using simulated and real test data.
Journal Article

Evaluation of Non-Uniform Upstream Flow Effects on Vehicle Aerodynamics

2014-04-01
2014-01-0614
Historically vehicle aerodynamic development has focused on testing under idealised conditions; maintaining measurement repeatability and precision in the assessment of design changes. However, the on-road environment is far from ideal: natural wind is unsteady, roadside obstacles provide additional flow disturbance, as does the presence of other vehicles. On-road measurements indicate that turbulence with amplitudes up to 10% of vehicle speed and dominant length scales spanning typical vehicle sizes (1-10 m) occurs frequently. These non-uniform flow conditions may change vehicle aerodynamic behaviour by interfering with separated turbulent flow structures and increasing local turbulence levels. Incremental improvements made to drag and lift during vehicle development may also be affected by this non-ideal flow environment. On-road measurements show that the shape of the observed turbulence spectrum can be generalised, enabling the definition of representative wind conditions.
Journal Article

Evaluation of the Aerodynamic and Aeroacoustic Response of a Vehicle to Transient Flow Conditions

2013-04-08
2013-01-1250
A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. Unsteady effects occurring in the sideglass region of a vehicle are particularly relevant to wind noise. This is a region close to the driver and dominated by separated flow structures from the A-pillar and door mirrors, which are sensitive to unsteadiness in the onset flow. Since the sideglass region is of particular aeroacoustic importance, the paper seeks to determine what impact these unsteady effects have on the sources of aeroacoustic noise as measured inside the passenger compartment, in addition to the flow structures in this region. Data presented were obtained during on-road measurement campaigns using two instrumented vehicles, as well as from aeroacoustic wind tunnel tests.
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