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Material Properties of Granular Ice Layers Characterized Using a Rigid-Body-Penetration Method: Experiments and Modeling

Technical University of Darmstadt-Markus Schremb, Kenan Malicevic, Louis Reitter, Ilia Roisman, Cameron Tropea
Published 2019-06-10 by SAE International in United States
Accretion and shedding of ice layers is a serious problem for various engineering applications. In particular, ice layers growing due to ice crystal impingement on warm parts of an aircraft jet engine pose a severe hazard since they seriously affect safe operation of an aircraft. The material properties, and in the first place the strength of an ice layer, are crucial for the mechanisms leading to, and taking place during, both accretion and shedding of an ice layer. In the present study, the apparent yield strength of dry granular ice layers is examined employing a novel rigid-body-penetration approach. Dynamic projectile penetration into granular ice layers of varying porosity and ice grain size is experimentally investigated for different projectile impact velocities using a high-speed video system and post-processing of the captured video data. The obtained data for the total penetration depth of the projectile is used to calculate the apparent yield strength of the ice layer based on theoretical modeling of the projectile dynamics during penetration. Finally, the experimental method and theoretical modeling employed in the…
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MUSIC-Haic: 3D Multidisciplinary Tools for the Simulation of In-Flight Icing due to High Altitude Ice Crystals

Darmstadt University of Technology-Ilia Roisman, Cameron Tropea
General Electric Aviation-Paolo Vanacore
Published 2019-06-10 by SAE International in United States
Icing is a major hazard for aviation safety. Over the last decades an additional risk has been identified when flying in clouds with high concentrations of ice-crystals where ice accretion may occur on warm parts of the engine core, resulting in engine incidents such as loss of engine thrust, strong vibrations, blade damage, or even the inability to restart engines. Performing physical engine tests in icing wind tunnels is extremely challenging, therefore, the need for numerical simulation tools able to accurately predict ICI (Ice Crystal Icing) is urgent and paramount for the aeronautics industry, especially regarding the development of new generation engines (UHBR = Ultra High Bypass Ratio, CROR = Counter rotating Open Rotor, ATP = Advanced Turboprop) for which analysis methods largely based on previous engines experience may be less and less applicable. The European research project MUSIC-haic has been conceived to fill this gap and has started in September 2018. MUSIC-haic brings together the main European research institutions working on icing modelling as well as engine manufacturers and aircraft manufacturers. The project will…
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Ice Nucleation in the Presence of Electric Fields: An Experimental Study

TU Darmstadt, High-Voltage Laboratories-Jens-Michael Löwe, Volker Hinrichsen
TU Darmstadt, SLA-Markus Schremb, Cameron Tropea
Published 2019-06-10 by SAE International in United States
In the present study, ice nucleation in sessile water drops during continuous cool down is studied experimentally under the impact of a constant electric field, to determine its influence on heterogeneous nucleation. The experimental setup enables simultaneous observation of multiple drops under well-defined conditions with and without an electric field and at temperatures down to -40 °C. A single experimental run contains 40 drops exposed to the same conditions. Drops with a well-defined size are produced employing a drop-on-demand drop generator. Based on multiple experimental runs using the same drops, the nucleation behavior is analyzed using statistical methods to determine the drop survival curves and nucleation site densities for varying conditions. Besides the influence of the electric field, the influence of different drop ensembles is investigated for a constant cooling rate of 5 K/min. A comparison of the experiments with and without an electric field is used to elaborate its influence on heterogeneous ice nucleation.
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Investigations on the Influence of Fuel Oil Film Interaction on Pre-ignition Events in Highly Boosted DI Gasoline Engines

Karlsruhe Institute of Technology-Heiko Kubach, Alex Weidenlener, Juergen Pfeil, Thomas Koch
Technische Universität Darmstadt-Hannah Kittel, Ilia V. Roisman, Cameron Tropea
Published 2018-04-03 by SAE International in United States
Premature and uncontrolled flame initiation, called pre-ignition (PI), is a prominent issue in the development of spark-ignited engines. It is commonly assumed that this abnormal combustion mode hinders progress in engine downsizing, thus inhibiting development of more efficient engines. The phenomenon is primarily observed in highly turbocharged spark ignited (SI) engines in the full load regime at low engine speeds. Subsequent engine knock induces extremely high peak pressures, potentially causing severe engine damage.The mechanisms leading to this phenomenon are not completely understood; however, it is quite plausible that a multiphase process is responsible for the pre-ignition. One effect could be the interaction between injected fuel drops and the oil film on the cylinder liner. Under certain conditions, droplets of oil or oil/fuel mixture can detach or splash from the film, leading to pre-ignition at the droplet surface towards the end of the compression phase.To gain further understanding of the possible mechanisms leading to pre-ignition events it is important to know under which conditions splash effects on the film can cause droplet detachment. In this paper…
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Scale-Resolving Simulation of an ‘On-Road’ Overtaking Maneuver Involving Model Vehicles

AVL LIST GmbH-Branislav Basara
Technical University of Darmstadt-Suad Jakirlic, Lukas Kutej, Cameron Tropea
Published 2018-04-03 by SAE International in United States
Aerodynamic properties of a BMW car model taking over a truck model are studied computationally by applying the scale-resolving PANS (Partially-averaged Navier-Stokes) approach. Both vehicles represent down-scaled (1:2.5), geometrically-similar models of realistic vehicle configurations for which on-road measurements have been performed by Schrefl (2008). The operating conditions of the modelled ‘on-road’ overtaking maneuver are determined by applying the dynamic similarity concept in terms of Reynolds number consistency. The simulated vehicle configuration constitutes of a non-moving truck model and a car model moving against the air flow, the velocity of which corresponds to the car velocity. The presently modelled ‘on-road’ overtaking maneuver is designed by reference to the complementary ‘quasi stationary’ event investigated experimentally in full-scale wind tunnel of the BMW Group in Munich/Ascheim by fixing the truck model at eight discrete positions relative to the car model, Schreffl (2008); accordingly, the results obtained are discussed also by reference to these measurements, in addition to the results of the realistic ‘on-road’ investigations. The turbulence modelling focus of the present work is on the validation of the…
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Critical Assessment of Some Popular Scale-Resolving Turbulence Models for Vehicle Aerodynamics

SAE International Journal of Passenger Cars - Mechanical Systems

Audi AG-Peter Unterlechner
Technical University of Darmstadt-Suad Jakirlic, Lukas Kutej, Cameron Tropea
  • Journal Article
  • 2017-01-1532
Published 2017-03-28 by SAE International in United States
Some widely-used scale-resolving turbulence models are comparatively assessed in simulating the aerodynamic behavior of a full-scale AUDI-A1 car configuration. The presently considered hybrid RANS/LES (RANS – Reynolds-Averaged Navier-Stokes; LES – Large-Eddy Simulation) models include the well-known DDES (Delayed Detached-Eddy Simulation) scheme and two further variable-resolution formulations denoted by PANS (Partially-Averaged Navier-Stokes; Basara, 2011) and VLES (Very LES; Chang et al., 2014). Whereas the DDES method represents the originally proposed formulation based on the one-equation Spalart-Almaras model (Spalart et al. 2006), whose RANS/LES interface position is directly correlated to the underlying grid resolution, the other two models represent ‘true’ seamless formulations, providing a smooth transition from Unsteady RANS to LES in terms of a dynamic “resolution parameter” variation. The latter parameter is evaluated by contrasting the length scale related to the residual turbulence of both PANS and VLES methods to the grid spacing. The dynamics of residual motion in both methods is modelled by a four equation model (Hanjalic et al., 2004). All computations are performed by the OpenFOAM code. The PANS and VLES formulations, in…
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Eddy-resolving Simulations of the Notchback ‘DrivAer’ Model: Influence of Underbody Geometry and Wheels Rotation on Aerodynamic Behaviour

AVL North America Inc.-Branislav Basara
Technical University of Darmstadt-Suad Jakirlic, Lukas Kutej, Daniel Hanssmann, Cameron Tropea
Published 2016-04-05 by SAE International in United States
The present work deals with a computational study of a ‘DrivAer’ car model, the rear-end shape of which corresponds to the Notchback configuration (Heft et al. [1] and Heft [2]). The study investigates the effects of the underbody geometry and wheel rotation on the aerodynamic performance. The configurations with detailed and smooth underbody as well as with stationary and rotating wheels are considered. The computational model applied relies on a VLES (Very Large Eddy Simulation) formulation, Chang et al. [3]. The residual turbulence related to the VLES framework is presently modelled by a RANS-based (Reynolds-Averaged Navier-Stokes), four-equation (D(k,ɛ,ζ, f)/Dt) near-wall eddy-viscosity model, Hanjalic et al. [4]. In addition to the equations governing the kinetic energy of turbulence (kus) and its dissipation rate (ɛus), it solves a transport equation for the quantity , representing a key parameter, as it models the velocity scale in the expression for the corresponding turbulence viscosity. In addition to VLES, all considered flows are simulated within both RANS and Unsteady RANS (URANS) frameworks using the same background model formulation representing the…
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Impact of Supercooled Liquid Drops onto Cold Solid Substrates

Technical Univ. of Darmstadt-Hai Li, Ilia Roisman, Cameron Tropea
Published 2015-06-15 by SAE International in United States
Airframe icing caused by supercooled large droplets (SLD) has been identified as a severe hazard in aviation. This study presents an investigation of impact of a supercooled drop onto superhydrophobic and partially wettable substrates. Drop impact, spreading and rebound were observed using a high-speed video system. The maximum spreading diameter of an impacting drop on partially wettable surfaces was measured. The temperature effect on this parameter was only minor for a wide range of the drop and substrate temperatures. However solidification hindered receding when both the drop and substrate temperatures were below 0°C. The minimum receding diameter and the speed of ice accretion on the substrate were measured for various wall and drop temperatures. The two parameters increased almost linearly with the decrease of the wall temperature, but eventually leveled off beyond a certain substrate temperature. The speed of ice accretion on the substrate was significantly higher than the growth rate of free ice dendrites at a certain supercooling. These disparities are attributed to formation of multiple initial nucleation sites and the liquid flow. These…
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Surface Energy Influence on Supercooled Water Crystallization: A Computational Study

TAKATA AG, EMEA New Devices Engineering-Antonio Criscione
Technical Univ. of Darmstadt-Suad Jakirlic, Ilia Roisman, Cameron Tropea
Published 2015-06-15 by SAE International in United States
Numerical experiments have been presently conducted aiming at studying the influence of the surface energy on the crystallization process of supercooled water in terms of the supercooling degrees. The mathematical model consists primarily of the equation governing the thermal energy field solved independently in both phases in accordance with the two-scalar approach by utilizing the Stefan condition at the interface to couple both temperature fields. The computational algorithm relying on the level-set method for solid-liquid interface capturing has been appropriately upgraded aiming at accuracy level increase with respect to the discretization of the thermal energy equation and the normal-to-interface derivative of the temperature field. The model describes the freezing mechanism under supercooled conditions, relying on the physical and mathematical description of the two-phase moving-boundary approach. The relevant numerical algorithm is implemented into the open source software OpenFOAM®. The results obtained illustrate the stabilizing effect of the surface energy compared to the level of supercooling. The effect of the anisotropy of the interfacial energy on the ice nucleus growth, resulting in a six-fold crystal shape, is…
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Computational Study of the Aerodynamics of a Realistic Car Model by Means of RANS and Hybrid RANS/LES Approaches

SAE International Journal of Passenger Cars - Mechanical Systems

AVL List GmbH-Branislav Basara
Technische Universitaet, Darmstadt-Suad Jakirlic, Lukas Kutej, Cameron Tropea
  • Journal Article
  • 2014-01-0594
Published 2014-04-01 by SAE International in United States
The aerodynamic properties of a BMW car model, representing a 40%-scaled model of a relevant car configuration, are studied computationally by means of the Unsteady RANS (Reynolds-Averaged Navier-Stokes) and Hybrid RANS/LES (Large-Eddy Simulation) approaches. The reference database (geometry, operating parameters and surface pressure distribution) are adopted from an experimental investigation carried out in the wind tunnel of the BMW Group in Munich (Schrefl, 2008). The present computational study focuses on validation of some recently developed turbulence models for unsteady flow computations in conjunction with the universal wall treatment combining integration up to the wall and high Reynolds number wall functions in such complex flow situations. The turbulence model adopted in both Unsteady RANS and PANS (Partially-Averaged Navier Stokes) frameworks is the four-equation ζ − f formulation of Hanjalic et al. (2004) based on the Elliptic Relaxation Concept (Durbin, 1991). The latter model mimics the sub-scale model in the PANS method representing a hybrid RANS/LES strategy, proposed recently by Basara et al. (2011). Herewith a seamless transition from Unsteady RANS to the direct numerical simulation (DNS)…
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