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A Priori Analysis of Acoustic Source Terms from Large-Eddy Simulation in Turbulent Pipe Flow

Graz University of Technology-Johannes Tieber, Helfried Steiner
  • Technical Paper
  • 2020-01-1518
To be published on 2020-06-03 by SAE International in United States
The absence of combustion engine noise pushes increasingly attention to the sound generation from other, even much weaker, sources in the acoustic design of electric vehicles. The present work focusses on the numerical computation of flow induced noise, typically emerging in components of flow guiding devices in electro-mobile applications. The method of Large-Eddy Simulation (LES) represents a powerful technique for capturing most part of the turbulent fluctuating motion, which qualifies this approach as a highly reliable candidate for providing a sufficiently accurate level of description of the flow induced generation of sound. Considering the generic test configuration of turbulent pipe flow, the present study investigates in particular the scope and the limits of incompressible Large-Eddy Simulation in predicting the evolution of turbulent sound sources to be supplied as source terms into acoustic analogies, which have been proposed for the computation of the acoustic pressure field. To this end, a comprehensive a priori analysis of fully resolved flow fields obtained from Direct Numerical Simulations (DNS) was carried out for different Reynolds numbers. The analysis of the…
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Numerical investigations on strong knocking combustion under compression ignition conditions

State Key Lab of Engines-Jiaying Pan
Tianjin University-Lin Chen, Jianfu Zhao
  • Technical Paper
  • 2020-01-1137
To be published on 2020-04-14 by SAE International in United States
Homogeneous charge compression ignition (HCCI) combined with high compression ratio is an effective way to improve engines’ thermal efficiency. However, the severe thermodynamic conditions at high load may induce knocking combustion thus damage engine body. In this study, compression ignition knocking characteristics were parametrically investigated through RCM experiments and simulation analysis. First, the knocking characteristics were optically investigated. The experimental results show that there even exists detonation when the knock occurs thus the combustion chamber is damaged. Considering both safety and costs, the effects of different initial conditions were numerically investigated and the results show that knocking characteristics is more related to initial pressure other than initial temperature. The initial pressure have a great influence on peak pressure and knock intensity while initial temperature on knock onset. Further analysis shows that knock intensity is mainly related to the energy density of the in-cylinder mixture and energy density is higher under higher pressure conditions. Then the effects of different cylinder wall temperature on the local auto-ignition thus knocking characteristics were further discussed. The results show that…
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Visualization of Turbulence Anisotropy in the In-cylinder Flow of Internal Combustion Engines

Graz University of Technology-Andreas Wimmer
LEC GmbH-Rajat Soni, Clemens Gößnitzer, Gerhard Pirker
  • Technical Paper
  • 2020-01-1105
To be published on 2020-04-14 by SAE International in United States
Turbulence anisotropy has a great influence on mixture formation and flame propagation in internal combustion engines. However, the visualization of turbulence in simulations is not straightforward; traditional methods lack the ability to display the anisotropic properties in the engine geometry. Instead, they use invariant maps, and important information about the locality of the turbulence anisotropy is lost. This paper overcomes this shortcoming by visualizing the anisotropy directly in the physical domain. Componentality contours are applied to directly visualize the anisotropic properties of turbulence in the three-dimensional engine geometry. Using an RGB (red, green, blue) color map, the three limiting states of turbulence (one-component, axisymmetric two-component and isotropic turbulence) are displayed in the three-dimensional physical domain. Thus, the assessment and interpretation of the results is straightforward and can easily be integrated into a normal post-processing workflow.This paper focuses on unsteady Reynolds-averaged Navier-Stokes equations methods and uses the RNG k-ε model in the simulations. Computational fluid dynamics simulations of the cold flow operation of a single-cylinder research engine demonstrate the strength of this visualization strategy. Different phases…
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The Prospect and Benefits of Using the Partial-Averaged Navier-Stokes Method for Engine Flows

AVL LIST GmbH-Branislav Basara, Zoran Pavlovic
Texas A&M University-Sharath Girimaji
  • Technical Paper
  • 2020-01-1107
To be published on 2020-04-14 by SAE International in United States
This paper presents calculations of engine flows by using the Partially-Averaged Navier Stokes (PANS) method (Girimaji [1]; [2]). The PANS is a scale-resolving turbulence computational approach designed to resolve large scale fluctuations and model the remainder with appropriate closures. Depending upon the prescribed cut-off length (filter width) the method adjusts seamlessly from the Reynolds-Averaged Navier-Stokes (RANS) to the Direct Numerical Solution (DNS) of the Navier-Stokes equations. The PANS method was successfully used for many applications but mainly on static geometries, e.g. Basara et al. [3]; [4]. This is due to the calculation of the cut-off control parameter which requires that the resolved kinetic energy is known and this is usually obtained by suitably averaging of the resolved field. Such averaging process is expensive and impractical for engines as it would require averaging per cycles. A recently published work on PANS (Basara et al. [5]) opens a prospect of more cost-effective engine calculations. This new PANS approach solves the additional equation for a total resolved turbulent kinetic energy which enables continuous (in situ) update of the…
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LES Modeling Study on Cycle-to-Cycle Variations in a DISI Engine

Honda R&D Co., Ltd.-Hiroyoshi Taniguchi
RWTH Aachen University-Tobias Falkenstein, Marco Davidovic, Antonio Attili, Mathis Bode, Hongchao Chu, Heinz Pitsch
  • Technical Paper
  • 2020-01-0242
To be published on 2020-04-14 by SAE International in United States
The reduction of cycle-to-cycle variations (CCV) is a prerequisite for the development and control of spark-ignition engines with increased efficiency and reduced engine-out emissions. To this end, Large-Eddy Simulations can improve the understanding of stochastic in-cylinder phenomena during the engine design process, if the employed modeling approach is sufficiently accurate. To assess the predictive capabilities of the turbulent combustion model used in this work, an engine-relevant Direct Numerical Simulation (DNS) dataset of premixed flame propagation in homogeneous isotropic turbulence is considered for a-posteriori investigations. LES predictions using the Flame Front / Progress Variable Equation Model are demonstrated to be in good agreement with the DNS results. Integral flame propagation results are shown to be unaffected by the choice of two eddy viscosity models, although some differences in the SFS velocity distributions near the flame front exist between the Dynamic Smagorinsky Model (DSM) and the Coherent Structure Model (CSM). The validated combustion model has been applied to investigate CCV in a direct-injected spark ignition (DISI) engine under fuel-lean conditions with respect to a stoichiometric baseline operating…
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Acoustic performance analysis of automotive HVAC duct designs using a Lattice-Boltzmann based method and correlation with Semi-anechoic chamber.

Dassault Systemes-Prasad Sivakumar, Adrien Mann, Minsuk Kim
FCA Engineering India Pvt., Ltd.-Sivaji Pasupuleti
  • Technical Paper
  • 2020-01-1263
To be published on 2020-04-14 by SAE International in United States
Acoustic comfort of automotive cabins has progressively become one of the key attributes of vehicle design, with wind noise and HVAC noise being two of the key contributors to noise levels heard inside the car. With the increasing prevalence of hybrid technologies and electrification and the associated reduction in powertrain noise levels, the industry has seen an increasing focus on understanding HVAC noise, as it is a main source of noise in the cabin if not the single one when the vehicle is stopped. The complex turbulent flow path through the ducts, combined with acoustic resonances can potentially lead to significant noise generation, both broadband and tonal. In order to avoid time consuming and expensive late stage design changes, or avoid being hit by low consumer rating ignoring the issues, it is important to identify potential problems early in the design process and take appropriate measures to rectify them. In this study, the noise characteristics of three HVAC duct designs are studied using a commercial CFD code based on the Lattice-Boltzmann method. The noise spectra…
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A Quasi-Dimensional SI Burn Rate Model for Predicting the Effects of Changing Fuel, Air-Fuel-Ratio, EGR and Water Injection

FKFS-Michael Grill
IVK, University of Stuttgart-Sebastian Hann, Michael Bargende
  • Technical Paper
  • 2020-01-0574
To be published on 2020-04-14 by SAE International in United States
As a result of the shifted R&D focus from internal combustion engines to electrified powertrains, resources for the development of internal combustion engines are restricted more and more. With that, the importance of highly efficient engine development tools is increased. In this context, 0D/1D engine simulation offers the advantage of low computational effort and fast engine model set-up. To ensure a high predictive ability of the engine simulation, a reliable combustion model is needed. Considering the increasing interest in alternative fuels, the aspect of predicting the fuel influence on combustion is of special importance. To reach these targets, the change of engine combustion characteristics with changing fuels and changing air-fuel-ratios is investigated systematically in a first step. For this purpose, engine test bed data is compared with expected fuel-dependent flame wrinkling trends based on Markstein / Lewis-number theory. Furthermore, the possibility of influences caused by the Darrieus-Landau instability is evaluated. Based on these comparisons, an existing combustion model is improved by adapting the sub-models for laminar and turbulent flame speed as well as the approach…
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Wake study on isolated, detailed and rotating car wheels

Audi AG-Lukas Haag, Vincent Zander
Technische Universitat Munchen-Jan Reiß, Jonas Sebald, Thomas Indinger
  • Technical Paper
  • 2020-01-0686
To be published on 2020-04-14 by SAE International in United States
Wheels on passenger vehicles cause about 25% of the aerodynamic drag. The interference of rims and tires in combination with the rotation result in strongly turbulent wake regions with complex flow phenomena. This wake structures interact with the flow around the vehicle. To understand the wake structures of wheels and their aerodynamic impact on the aerodynamic drag of the vehicle, the complexity was reduced by investigating a standalone tire in the windtunnel. Besides the influence of geometry changes on the acting forces, the wake region behind the wheel is investigated via Particle Image Velocimetry (PIV). The average flow field behind the investigated wheels is captured with this method and offers insight into the flow field. The investigation of the wake region allows to attribute changes in the flow field to the change of tires and rims. Due to increased calculation performance sophisticated CFD simulations can capture detailed geometries like the tire tread and the movement of the rim. Therefore, the wake investigation via PIV is a usable basis to compare it to results of such…
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Simulation of Transient On-Road Conditions in a Closed Test Section Wind Tunnel Using a Wing System with Active Flaps

FKFS-Andreas Wagner, Jochen Wiedemann
German Aerospace Center DLR-Henning Wilhelmi, James Bell, Daniela Heine, Claus Wagner
  • Technical Paper
  • 2020-01-0688
To be published on 2020-04-14 by SAE International in United States
Typical automotive research in wind tunnels is conducted under idealized, stationary, low turbulence flow conditions. This does not necessarily reflect the actual situation in traffic. Thus, there is a considerable interest to simulate the actual flow conditions. Because of this, a system for the simulation of the turbulence intensity I, the integral linear scale L and the transient angle of incidence β measured in full-scale tests in the inflow of a test vehicle was developed and installed in a closed-loop, closed test section wind tunnel. The system consists of four airfoils with movable flaps and is installed in the beginning of the test section. Time-series of the flow velocity vector are measured in the empty test section to analyze the system’s envelope in terms of the turbulence intensity and the integral length scales. It is shown that the length scales in spanwise and in driving (streamwise) direction can be varied from 0.15 m to 7.9 m and from 0.15 m to 2.5 m, respectively, depending on the frequency of the flap movement. The maximum obtained…
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Measurements and Correlations of Local Cylinder-Wall Heat-Flux Relative to Near-Wall Chemiluminescence across Multiple Combustion Modes

Zachary Shechtman
Sandia National Laboratories-Zheming Li, Mark Musculus
  • Technical Paper
  • 2020-01-0802
To be published on 2020-04-14 by SAE International in United States
Minimizing heat transfer (HT) losses is important for both improving engine efficiency and increasing exhaust energy for turbocharging and exhaust aftertreatment management, but engine combustion system design to minimize these losses is hindered by significant uncertainties in prediction. Empirical HT correlations such as the popular Woschni model have been developed and various attempts at improving predictions have been proposed since the 1960s, but due to variations in facilities and techniques among various studies, comparison and assessment of modelling approaches among multiple combustion modes is not straightforward. In this work, simultaneous cylinder-wall temperature and OH* chemiluminescence high-speed video are all recorded in a single heavy-duty optical engine operated under multiple combustion modes. The cylinder-wall HT is derived from the measured transient temperature and compared with Woschni HT correlation predictions using both bulk and estimated local gas-temperatures. The local Woschni correlation predictions of heat flux and the HT coefficient for spark ignition (SI) and homogeneous charge compression ignition (HCCI) match surprisingly well with measurements. Uncertainty analysis shows that the modeled results falls in the measurements uncertainty. For…