TY - CHAP A1 - Kerstein, Alan R. A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Klein, Rupert A1 - Gonzalez-Juez, Esteban D. A1 - Schmidt, Rodney T1 - Computational modeling of scalar transport and buoyancy effects in turbulent flows using ODTLES T2 - Bulletin of the American Physical Society Y1 - 2012 UR - http://meeting.aps.org/Meeting/DFD12/Event/176984 N1 - 65th Annual Meeting of the APS Division of Fluid Dynamics, Sunday–Tuesday, November 18–20, 2012 San Diego, California VL - 57 IS - 17 ER - TY - GEN A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko A1 - Peters, Norbert T1 - Probability density functions in the cloud-top mixing layer Y1 - 2010 UR - http://iopscience.iop.org/1367-2630/12/8/085010/pdf/1367-2630_12_8_085010.pdf ER - TY - GEN A1 - Schmidt, Heiko A1 - Jiménez, Carmen T1 - Numerical study of the direct pressure effect of acoustic waves in planar premixed flames T2 - Combustion and Flame Y1 - 2010 UR - http://www.sciencedirect.com/science/article/pii/S001021801000088X SN - 1556-2921 VL - 157 IS - 8 SP - 1610 EP - 1619 ER - TY - GEN A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko A1 - Peters, Norbert T1 - Two-fluid formulation of the cloud-top mixing layer for direct numerical simulation T2 - Theoretical and computational fluid dynamics N2 - A mixture fraction formulation to perform direct numerical simulations of a disperse and dilute two-phase system consisting of water liquid and vapor in air in local thermodynamic equilibrium using a twofluid model is derived and discussed. The goal is to understand the assumptions intrinsic to this simplified but commonly employed approach for the study of two-layer buoyancy reversing systems like the cloud-top mixing layer. Emphasis is placed on molecular transport phenomena. In particular, a formulation is proposed that recovers the actual nondiffusive liquid-phase continuum as a limiting case of differential diffusion. High-order numerical schemes suitable for direct numerical simulations in the compressible and Boussinesq limits are described, and simulations are presented to validate the incompressible approach. As expected, the Boussinesq approximation provides an accurate and efficient description of the flow on the scales (of the order of meters) that are considered. KW - Free convection KW - Free turbulent flows KW - Multiphase KW - Stratocumulus clouds Y1 - 2010 U6 - https://doi.org/10.1007/s00162-010-0182-x SN - 1432-2250 SN - 0935-4964 VL - 24 IS - 6 SP - 511 EP - 536 ER - TY - GEN A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko A1 - Peters, Norbert T1 - Buoyancy reversal in cloud-top mixing layers T2 - Quarterly Journal of the Royal Meteorological Society Y1 - 2009 U6 - https://doi.org/10.1002/qj.417 SN - 1477-870X VL - 135 IS - 641 SP - 963 EP - 978 ER - TY - GEN A1 - Moeck, Jonas Pablo A1 - Oevermann, Michael A1 - Klein, Rupert A1 - Paschereit, Christian Oliver A1 - Schmidt, Heiko T1 - A two-way coupling for modeling thermoacoustic instabilities in a flat flame Rijke tube T2 - Proceedings of the Combustion Institute Y1 - 2009 U6 - https://doi.org/10.1016/j.proci.2008.05.062 SN - 1540-7489 VL - 32 IS - 1 SP - 1199 EP - 1207 ER - TY - CHAP A1 - Mellado, Juan Pedro A1 - Schmidt, Heiko A1 - Stevens, Bjorn A1 - Peters, Norbert T1 - Analysis of the cloud top mixing layer using DNS Y1 - 2009 ER - TY - RPRT A1 - Schmidt, Heiko A1 - Jiménez, Carmen T1 - Numerical study of the direct pressure effect of acoustic waves in planar premixed flames Y1 - 2009 UR - http://www.zib.de/de/numerik/publikationen.html#L2009 SN - 1438-0064 N1 - ZIB-Report 09-31 ER - TY - GEN A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - Numerical study of radiatively induced entrainment T2 - Journal of Physics: Conference Series Y1 - 2011 U6 - https://doi.org/10.1088/1742-6596/318/7/072017 SN - 1742-6588 VL - 318 SP - 072017 ER - TY - GEN A1 - Jiménez, Carmen A1 - Quinard, Joël A1 - Graña-Otero, Josè A1 - Schmidt, Heiko A1 - Searby, Geoff T1 - Unsteady response of hydrogen and methane flames to pressure waves T2 - Combustion and Flame Y1 - 2012 SN - 1556-2921 SN - 0010-2180 VL - 159 IS - 5 SP - 1894 EP - 1908 ER - TY - GEN A1 - Dietze, Eckhard A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko T1 - Study of low-order numerical effects in the two-dimensional cloud-top mixing layer T2 - Theoretical Computational Fluid Dynamic Y1 - 2012 U6 - https://doi.org/doi:10.1007/s00162-012-0263-0 SN - 0935-4964 ER - TY - GEN A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - Analysis and numerical simulation of a laboratory analog of radiatively induced cloud-top entrainment T2 - Theoretical Computational Fluid Dynamics Y1 - 2012 U6 - https://doi.org/10.1007/s00162-012-0288-4 SN - 1432-2250 ER - TY - CHAP A1 - Schmidt, Heiko A1 - Klein, Rupert ED - Warnecke, Gerald T1 - Flexible flame structure modelling in a Flame Front Tracking Scheme T2 - Analysis and Numerics for Conservation Laws Y1 - 2005 SN - 978-3-540-24834-7 SP - 405 EP - 427 PB - Springer CY - Heidelberg ER - TY - GEN A1 - Schmidt, Heiko A1 - Klein, Rupert T1 - A generalized level-set/in-cell-reconstruction approach for accelerating turbulent premixed flames T2 - Combustion Theory and Modelling N2 - An extended numerical technique for the simulation of accelerating turbulent premixed flames in large scale geometries is presented. It is based on a hybrid capturing tracking technique. It resembles a tracking scheme in that the front geometry is explicitly computed using a level-set method. The basic flow properties are provided by solving the compressible flow equations. The flame-flow-coupling is achieved by an in-cell-reconstruction technique. In cells cut by the flame, the discontinuous solution is reconstructed from given cell averages by invoking explicitly some Rankine-Hugoniot type jump conditions. Then the reconstructed states and again the front geometry are used to define accurate effective numerical fluxes across grid cell interfaces intersected by the front during the time step considered. Hence, the scheme also resembles a capturing scheme in that only cell averages of conserved quantities are computed. To be able to model inherently unsteady effects, like quenching, reignition, etc, during flame acceleration, we modified the standard Rankine-Hugoniot jump conditions. A source term appearing in the& modified jump conditions is computed by evaluating a suitable functional on the basis of a one-dimensional flame structure module, that is attached in the normal direction to the flame front. This module additionally yields quantities such as the net mass burning rate, necessary for the propagation of the level set, and the specific heat release important for the energy release due to the consumption of fuel. Generally, the flame structure calculation takes into account internal physical effects which are not active in the outer flow but essential for the front motion and its feedback on the surrounding fluid. If a suitable set of different (turbulent) combustion models to compute the flame structure is provided, the new numerical technique allows us to consistently represent laminar deflagrations, fast turbulent deflagrations as well as detonation waves. Supplemented with suitable criteria that capture the essence of a deflagration-to-detonation-transition (DDT), the complete evolution of such an event can be implemented in principle. Y1 - 2003 U6 - https://doi.org/10.1088/1364-7830/7/2/303 SN - 1364-7830 VL - 7 IS - 2 SP - 243 EP - 267 ER - TY - GEN A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - HCCI combustion modeling using detailed chemistry coupled to LEM-based advection T2 - Combustion and Flame Y1 - 2008 SN - 1556-2921 VL - 155 IS - 3 SP - 370 EP - 379 ER - TY - GEN A1 - Schulz, Falko T. A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Toward modeling of CO2 multi-phase flow patterns using a stochastic multi-scale approach T2 - Environmental Earth Sciences Y1 - 2013 U6 - https://doi.org/10.1007/s12665-013-2461-5 SN - 1866-6299 VL - 70 IS - 8 SP - 3739 EP - 3748 ER - TY - CHAP A1 - Schulz, Falko T. A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Liquid jet simulation using one-dimensional turbulence T2 - 14th European Turbulence Conference, Lyon, France, September 1-4, 2013 Y1 - 2013 UR - http://etc14.ens-lyon.fr/etc-14-proceedings/accepted-talks/ ER - TY - CHAP A1 - Schulz, Falko T. A1 - Glawe, Christoph A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Toward modeling of supercritical CO2 flow using map-based advection T2 - EGU General Assembly 2012, held 22-27 April, 2012 in Vienna Y1 - 2012 UR - http://meetingorganizer.copernicus.org/EGU2012/EGU2012-8816-1.pdf N1 - EGU2012-8816-1 ER - TY - CHAP A1 - Schmidt, Heiko A1 - Jozefik, Zoltan A1 - Jimenez, Carmen T1 - Detailed numerical simulation of forced planar premixed flames T2 - Book of abstracts, 34th International Symposium on Combustion, July 29 - August 3, Warsaw, Poland Y1 - 2012 UR - http://www.combustion2012.itc.pw.edu.pl/files/wip%20posters.pdf UR - http://www.combustion2012.itc.pw.edu.pl/files/W2P097-101.pdf N1 - W2P097 PB - The Combustion Institute, University of Technology CY - Warsaw ER - TY - CHAP A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Modeling of wind-field fluctuations using the one-dimensional-turbulence model T2 - The Science of Making Torque from Wind, Oldenburg, Germany, October 9-11, 2012 Oldenburg Germany Y1 - 2012 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2012_Forwind_Oldenburg.pdf ER - TY - CHAP A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko A1 - Peters, Norbert T1 - The evaporatively driven cloud-top mixing layer T2 - 63rd Annual Meeting of the APS Division of Fluid Dynamics Y1 - 2010 UR - http://meetings.aps.org/Meeting/DFD10/Event/133816 ER - TY - CHAP A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Towards a multiscale strategy for modeling high-pressure flow of carbon dioxide for sequestration T2 - Geoenergy 2010, Potsdam, Germany Y1 - 2010 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2010_GeoEn_Potsdam.pdf ER - TY - CHAP A1 - Kumar, Suvarchal Kumar A1 - Stevens, Björn A1 - Schmidt, Heiko A1 - Mellado, Juan Pedro T1 - Sensitivity of the ECHAM6 Single Column Model to Vertical Resolution and Implementation of the Level Set Method T2 - EGU General Assembly 2010, held in Vienna, Austria, 02 – 07 May 2010 Y1 - 2010 UR - http://meetingorganizer.copernicus.org/EGU2010/EGU2010-13511.pdf N1 - EGU2010-13511 PB - European Geophysical Society CY - Katlenburg-Lindau ER - TY - CHAP A1 - Dietze, Eckhard A1 - Stevens, Bjorn A1 - Mellado, Juan Pedro A1 - Peters, Norbert A1 - Schmidt, Heiko T1 - Level set methods for meteorological multi scale problems T2 - EGU General Assembly 2010, held in Vienna, Austria, 02 – 07 May 2010 Y1 - 2010 UR - http://meetingorganizer.copernicus.org/EGU2010/EGU2010-10083.pdf N1 - EGU2010-10083 ER - TY - CHAP A1 - Nédélec, Renaud A1 - Schmidt, Heiko A1 - Wunsch, Scott A1 - Sayler, Ben J. A1 - Kerstein, Alan R. T1 - Comparison of Entrainment Rates from a Tank Experiment with Results Us- ing the One-Dimensional-Turbulence Model T2 - EGU General Assembly 2010, held in Vienna, Austria, 02 – 07 May 2010 Y1 - 2010 UR - http://meetingorganizer.copernicus.org/EGU2010/EGU2010-378-1.pdf N1 - EGU2010-378-1 ER - TY - CHAP A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Linear eddy modeling of n-heptane combustion in HCCI engines T2 - 12th SIAM International Conference on Numerical Combustion Y1 - 2008 UR - http://www.siam.org/meetings/nc08/prgNC08.pdf ER - TY - GEN A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - One-dimensional turbulence simulation of a laboratory analog of radiatively induced cloud-top entrainment Y1 - 2011 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2011_Metstroem_Berlin.pdf N1 - MetStröm Conference 2011 on Multiple Scales in Fluid Dynamics and Meteorology ER - TY - CHAP A1 - Dietze, Eckhard A1 - Schmidt, Heiko A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn T1 - LES vs. DNS simulation of a two-dimensional evaporatively driven cloud-top mixing layer T2 - Conference on Multiple Scales in Fluid Dynamics and Meteorology Y1 - 2011 UR - http://metstroem.mi.fu-berlin.de/wp/wp-content/uploads/2012/06/Eckhard-Dietze.pdf ER - TY - CHAP A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko A1 - Peters, Norbert T1 - Buoyancy reversal in the cloud-top mixing layer T2 - 4th IMS Turbulence Workshop, Workshop, 23-25 March 2009, Y1 - 2009 UR - http://publications.mi.fu-berlin.de/711/ ER - TY - CHAP A1 - Schmidt, Heiko A1 - Schulz, Falko T. A1 - Kerstein, Alan R. T1 - Toward modeling of multi- phase flow patterns using a combination of level sets and one-dimensional turbulence T2 - EGU General Assembly 2011, Vienna, Austria, 03 – 08 April 2011 Y1 - 2011 UR - http://meetingorganizer.copernicus.org/EGU2011/EGU2011-10258.pdf N1 - EGU2011-10258 ER - TY - CHAP A1 - Jimenez, Carmen A1 - Moeck, J. A1 - Schmidt, Heiko T1 - Comparison of transfer functions of acoustically forced planar premixed hydrogen and methane flames T2 - 13th International Conference on Numerical Combustion, April 27-29, 2011, Corfu, Greece Y1 - 2011 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2011_ICNC_Corfu.pdf ER - TY - CHAP A1 - Mellado, Juan Pedro A1 - Schmidt, Heiko A1 - Stevens, Bjorn A1 - Peters, Norbert T1 - DNS of the turbulent cloud-top mixing layer T2 - Advances in turbulence XII, proceedings of the 12th EUROMECH European Turbulence Conference, September 7 - 10, 2009, Marburg, Germany Y1 - 2009 SN - 978-3-642-03084-0 SP - 401 EP - 404 PB - Springer CY - Berlin [u.a.] ER - TY - CHAP A1 - Dietze, Eckhard A1 - Schmidt, Heiko A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn T1 - Comparison of LES and DNS results for a two-dimensional evaporatively driven cloud-top mixing layer T2 - EGU General Assembly 2011, Vienna, Austria, 03 – 08 April 2011 Y1 - 2011 UR - http://meetingorganizer.copernicus.org/EGU2011/EGU2011-12553.pdf ER - TY - CHAP A1 - Schmidt, Heiko A1 - Jimenez, Carmen T1 - Unsteady response of premixed flames to acoustic pressure pulses under variation of the complexity of the reaction mechanism T2 - Fourth European Combustion Meeting (ECM) Y1 - 2009 UR - http://www.combustion.org.uk/ECM_2009/P810288.pdf ER - TY - CHAP A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko A1 - Peters, Norbert T1 - Investigation of the Cloud-Top Interface Using Direct Numerical Simulation T2 - Oberwolfach reports, Mathematical Theory and Modelling in Atmosphere-Ocean Science Y1 - 2010 U6 - https://doi.org/10.4171/OWR/2010/34 VL - 7 IS - 3 SP - 2061 EP - 2062 ER - TY - GEN A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - Analysis and numerical simulation of a laboratory analog of radiatively induced cloud-top entrainment T2 - Bulletin of the American Physical Society Dynamics Y1 - 2010 UR - http://meetings.aps.org/Meeting/DFD10/Event/133814 N1 - 63rd Annual Meeting of the APS Division of Fluid Dynamics, November 21–23, 2010, Long Beach, California VL - 55 IS - 16 ER - TY - CHAP A1 - Schmidt, Heiko A1 - Mellado, Juan Pedro A1 - Peters, Norbert A1 - Stevens, Bjorn T1 - Towards a modular superparameterization for Stratocumulus clouds considering unsteady entrainment T2 - 4th PAN-GCSS Meeting on Advances in modeling and observing clouds and convection, 2-6 June 2008, Toulouse, France Y1 - 2008 UR - http://www.knmi.nl/~siebesma/PAN-GCSS/abstracts_poster_session_2_wednesday.pdf ER - TY - CHAP A1 - Schmidt, Heiko A1 - Mellado, Juan Pedro A1 - Peters, Norbert A1 - Stevens, Bjorn T1 - Towards modular front tracking for Stratocumulus clouds considering unsteady entrainment processes T2 - European Geosciences Union General Assembly 2008, Vienna, Austria, 13 – 18 April 2008 Y1 - 2008 UR - http://www.cosis.net/members/meetings/abstracts/file.php/49/102930/pdf/EGU2008-A-04762.pdf N1 - EGU2008-A-04762 PB - European Geophysical Society CY - Katlenburg-Lindau ER - TY - CHAP A1 - Glawe, Christoph A1 - Klein, Rupert A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Towards the simulation of gravity waves using the One-Dimensional Turbulence model T2 - EGU General Assembly 2012, held 22-27 April, 2012 in Vienna Y1 - 2012 UR - http://meetingorganizer.copernicus.org/EGU2012/EGU2012-4821.pdf N1 - EGU2012-4821 ER - TY - CHAP A1 - Jimenez, Carmen A1 - Jozefik, Zoltan A1 - Schmidt, Heiko T1 - Detailed numerical simulation of forced planar premixed hydrocarbon flames T2 - Conference on Modelling Fluid Flow (CMFF'12), September 4, 2012 – September 7, 2012 Y1 - 2012 UR - http://www.ara.bme.hu/ocs/index.php/cmff/cmff012/paper/view/265 CY - Budapest ER - TY - CHAP A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko A1 - Peters, Norbert T1 - New results about the cloud-top entrainment instability T2 - Conference on Multiple Scales in Fluid Dynamics and Meteorology Y1 - 2011 UR - http://metstroem.mi.fu-berlin.de/wp/wp-content/uploads/2012/06/Juan-Pedro-Mellado.pdf ER - TY - CHAP A1 - Jimenez, Carmen A1 - Schmidt, Heiko T1 - Numerical simulation of the unsteady response of planar flames to acoustic waves T2 - CIEMAT, Madrid, Spain, May 21st 2009 Y1 - 2009 UR - http://www.seic09.eis.uva.es/Presentaciones/PN10.pdf ER - TY - CHAP A1 - Schmidt, Heiko A1 - Jimenez, Carmen T1 - Numerical study of the response of OH* chemiluminescence in planar premixed flames to acoustic forcing T2 - Proceedings of SPEIC10: Towards Sustainable Combustion, Tenerife 16-18 June 2010 Y1 - 2010 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2010_SPEIC_Tenerife.pdf ER - TY - GEN A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko T1 - Wind shear and buoyancy reversal at the stratocumulus top T2 - Journal of the Atmospheric Sciences N2 - A numerical experiment is designed to study the interaction at the stratocumulus top between a mean vertical shear and the buoyancy reversal due to evaporative cooling, without radiative cooling. Direct numerical simulation is used to eliminate the uncertainty introduced by turbulence models. It is found that the enhancement by shear-induced mixing of the turbulence caused by buoyancy reversal can render buoyancy reversal comparable to other forcing mechanisms. However, it is also found that (i) the velocity jump across the capping inversion Du needs to be relatively large and values of about 1ms21 that are typically associated with the convective motions inside the boundary layer are generally too small and (ii) there is no indication of cloud-top entrainment instability. To obtain these results,parameterizations of the mean entrainment velocity and the relevant time scales are derived from the study of the cloud-top vertical structure. Two overlapping layers can be identified: a background shear layer with a thickness (1/3)(Du)2/Db, where Db is the buoyancy increment across the capping inversion and a turbulence layer dominated by free convection inside the cloud and by shear production inside the relatively thin overlap region. As turbulence intensifies, the turbulence layer encroaches into the background shear layer and defines thereby the entrainment velocity. Particularized to the first research flight of the Second Dynamics andChemistry of theMarine Stratocumulus (DYCOMS II) field campaign, the analysis predicts an entrainment velocity of about 3mms21 after 5–10 min—a velocity comparable to the measurements and thus indicative of the relevance of mean shear in that case. Y1 - 2013 UR - http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-13-0189.1 SN - 1520-0469 VL - 71 IS - 3 SP - 1040 EP - 1057 ER - TY - CHAP A1 - Movaghar, Amirreza A1 - Linne, Mark A1 - Oevermann, Michael A1 - Meiselbach, Falko T. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Numerical study of liquid breakup at the surface of turbulent liquid jets using One-Dimensional Turbulence T2 - 26th Annual Conference on Liquid Atomization and Spray Systems, ILASS, proceedings of the Conference, Bremen, Germany, 08.09.2014 - 10.09.2014 N2 - This paper presents an investigation of primary breakup of planar turbulent liquid jets and breakup properties at the surface of turbulent jets in still air at standard conditions. Numerical simulations are carried out for jet exit Reynolds number 23000 and Weber numbers in the range [102–107]. Due to the limitation of direct numerical simulation (DNS) to moderate Reynolds numbers, a stochastic 1D ansatz based on the one-dimensional turbulence (ODT) model is used to simulate a planar liquid jet with a high lateral resolution. ODT permits an affordable high resolution of interface and single-phase property gradients which are key for understanding the local behavior. ODT is a stochastic model simulating turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. The most relevant mechanisms that influence the primary breakup of liquid jets are found to be represented accurately based on comparisons to experiments and correlations reported in the literature. Building on this finding, future work will focus on the statistics of droplets generated by primary breakup, both to investigate their relationship to breakup mechanisms and to provide input to models of secondary breakup and subsequent spray evolution. Y1 - 2014 SN - 978-3-00-047070-7 CY - Bremen ER - TY - CHAP A1 - Mellado, Juan Pedro A1 - Stevens, Bjorn A1 - Schmidt, Heiko T1 - Wind shear and evaporative cooling at the stratocumulus top T2 - 21st Symposium on Boundary Layers and Turbulence, 9-13 June 2014, Leeds, United Kingdom N2 - Turbulent entrainment at the stratocumulus top and its interaction with local processes like radiative or evaporative cooling still remains a source of uncertainty in current atmospheric models. The reason is, at least partly, that the characteristic scales at which those cloud-top processes occur are relatively small, of the order of a few tens of meters, and access to accurate data at those scales has been difficult. In this contribution, we present a simplified model designed to investigate these cloud-top processes in detail and we address some questions regarding the role of buoyancy reversal by evaporative cooling at the cloud top. As a tool, we use direct numerical simulation to remove the uncertainty associated with turbulence models. Buoyancy reversal refers to the formation of negatively buoyant parcels of fluid within an otherwise stable stratification as a consequence of the local cooling caused by the evaporation of the droplets at the cloud interface. This process leads to convective instability, as heavier parcels of fluid lie on top of lighter ones. This instability promotes turbulence, and hence entrainment and further evaporation of droplets, a feedback process that could eventually lead to a rapid dessication of the cloud -- the so-called cloud-top entrainment instability. Recent work has demonstrated that, in contrast to previous postulates, buoyancy reversal caused by evaporative cooling is not a sufficient condition to break up the cloud: turbulence is indeed enhanced, but very mildly. The reason is that buoyancy reversal alone leads to a meta-stable layer as the mixing rate, or entrainment rate, is diffusively limited, so that the eventual breakup of the cloud by buoyancy reversal alone occurs on time scales that are much too long to be relevant to the stratocumulus-top boundary layer. To become relevant, evaporative cooling requires the interaction with other local mechanisms of turbulence generation, like wind shear or radiative cooling. In this work, we study wind shear effects, without radiative cooling. There are at least two reasons to study shear effects. First, shear is ubiquitous, as local shear associated with large-scale eddies will also be evident even in the absence of a mean wind. Second, shear alone cannot sustain a continuous deepening of the layer, as shear generated turbulence will locally thicken the entrainment zone, but in the absence of other sources, the turbulence will eventually decay once a critical entrainment-zone thickness is reached. The latter makes it interesting to combine shear with the convective destabilization of the cloud-top layer through buoyancy reversal, as neither process acting alone is efficient in supporting significant mixing at the cloud top. In contrast, by generating convective eddies which locally thin the entrainment zone, buoyancy reversal might help enhance shear, which in turn locally enhances the mixing which sustains the buoyancy reversal, raising the possibility that the processes are self-reinforcing. Results show that the enhancement by local wind shear can render buoyancy reversal comparable to other forcing mechanisms. However, we also find that (i) the velocity jump across the capping inversion, Δu, needs to be relatively large and typical values of about 1 m s-1 associated with the convective motions inside the boundary layer are generally too small, and (ii) there is no indication of cloud-top entrainment instability. To obtain these results, parametrizations of the mean entrainment velocity and the relevant time scales are derived from the study of the cloud-top vertical structure. Two overlapping layers can be identified: a background shear layer with a thickness (1/3) (Δu)2/(Δb), where Δb is the buoyancy increment across the capping inversion, and a turbulence layer dominated by free convection inside the cloud and by shear production inside the relatively thin overlap region. As turbulence intensifies, the turbulence layer encroaches into the background shear layer and defines thereby the entrainment velocity. Particularized to the first research flight of the Second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field campaign, the analysis predicts an entrainment velocity of about 3 mm s-1 after 5-10 minutes, a velocity comparable to the measurements and thus indicative of the relevance of mean shear in that case. Y1 - 2014 UR - https://ams.confex.com/ams/21BLT/webprogram/Paper247674.html ER - TY - CHAP A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - ODTLES: Mulitscale turbulence modeling and buoyant application T2 - Book of abstracts, 7th European Postgraduate Fluid Dynamics Conference, Ilmenau, Germany, 14th - 17th, July 2014 Y1 - 2014 CY - Ilmenau ER - TY - GEN A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Lyra, Sgouria A1 - Kolla, Hemanth A1 - Chen, Jackie H. T1 - One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS T2 - Combustion and Flame Y1 - 2014 SN - 1556-2921 VL - 162 IS - 8 SP - 2999 EP - 3015 ER - TY - GEN A1 - Schmidt, Heiko A1 - Glawe, Christoph A1 - Jozefik, Zoltan A1 - Meiselbach, Falko T. A1 - Kerstein, Alan R. T1 - On the benefits of ODT-based stochastic turbulence modeling T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - We summarize the group’s progress in applying, analyzing, and improving ODT and ODT-based stochastic turbulence models like ODTLES. Compared to DNS these models span a wider range of scales while compared to RANS/LES (i) the molecular effects are retained and (ii) no assumption of scale separation is made. In this regard ODTLES has more properties of DNS than of standard LES. Y1 - 2014 SN - 1617-7061 VL - 14 IS - 1 SP - 655 EP - 656 ER - TY - CHAP A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko ED - King, Rudibert T1 - Towards a compressible reactive multiscale approach based on One-Dimensional Turbulence T2 - Active Flow and Combustion Control 2014 N2 - Due to its huge complexity, progress in understanding and prediction of turbulent combustion is extremely challenging. In principle, progress is possible without improved understanding through direct numerical solution (DNS) of the exact governing equations, but the wide range of spatial and temporal scales often renders it unaffordable, so coarse-grained 3D numerical simulations with subgrid parameterization of the unresolved scales are often used. This is especially problematic for multi-physics regimes such as reacting flows because much of the complexity is thus relegated to the unresolved small scales. One-Dimensional Turbulence (ODT) is an alternative stochastic model for turbulent flow simulation. It operates on a 1D spatial domain via time advancing individual flow realizations rather than ensemble-averaged quantities. The lack of spatial and temporal filtering on this 1D domain enables a physically sound multiscale treatment which is especially useful for combustion applications where, e.g., sharp interfaces or small chemical time scales have to be resolved. Lignell et al. recently introduced an efficient ODT implementation using an adaptive mesh. As all existing ODT versions it operates in the incompressible regime and thus cannot handle compressibility effects and their interactions with turbulence and chemistry which complicate the physical picture even further. In this paper we make a first step toward an extension of the ODT methodology towards an efficient compressible implementation. The necessary algorithmic changes are highlighted and preliminary results for a standard non-reactive shock tube problem as well as for a turbulent reactive case illustrate the potential of the extended approach. Y1 - 2014 SN - 978-3-319-11967-0 SN - 978-3-319-11966-3 SP - 197 EP - 211 PB - Springer CY - Switzerland ER -