Journal: Flow, Turbulence and Combustion

Abbreviation

Flow Turbulence Combust

Publisher

Springer

Journal Volumes

ISSN

1386-6184
1573-1987

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Publications 1 - 10 of 25
  • On the relation between fronts and high-shear layers in wall turbulence
    Item type: Journal Article
    Wilhelm, Dirk; Härtel, Carlos; Eckelmann, Helmut (1998)
    Flow, Turbulence and Combustion
  • Retracted: Evaluation of the Filtered Noise Turbulent Inflow Generation Method
    Item type: Journal Article
    Allegrini, Jonas; Carmeliet, Jan (2017)
    Flow, Turbulence and Combustion
    Flows around buildings and in urban areas have the ability to exchange mass and momentum through mixing layers. The complex dynamical phenomena arising in mixing layers can be studied using Large Eddy Simulation (LES). As mixing layers depend on the turbulence conditions upstream of the buildings or urban areas, appropriate turbulent inlet conditions have to be provided to a simulation. Due to the high efficiency and level of control, the filtered noise inflow method was selected. The control over the Reynolds stresses as well as nine length scales make this method suitable to replicate conditions measured in experiments. In this paper, a formal method to obtain the filter coefficients is presented. This is achieved by relating the spatial filtering to a Finite Impulse Response (FIR) filter and the temporal filtering to an Autoregressive (AR) model. Three closed-form solutions for the spatial filter coefficients are presented having a Gaussian, double-exponential and exponential correlation function. By means of an LES simulation of a turbulent wall-bounded flow, the input-output behaviour is investigated. It was found that a combination of a Gaussian filter with length scales that increase with increasing wall distance result in the fastest downstream development of the artificial turbulence and the smallest loss of turbulent kinetic energy.
  • LES of the Gas-Exchange Process Inside an Internal Combustion Engine Using a High-Order Method
    Item type: Journal Article
    Giannakopoulos, George K.; Frouzakis, Christos E.; Fischer, Paul F.; et al. (2020)
    Flow, Turbulence and Combustion
  • Dynamic response of turbulent low emission flames at different vortex breakdown conditions
    Item type: Journal Article
    Biagioli, Fernando; Paikert, Bettina; Génin, Franklin; et al. (2013)
    Flow, Turbulence and Combustion
  • OH Concentration Measurements by Resonant Holographic Interferometry and Comparison with Direct Numerical Simulations
    Item type: Journal Article
    Tzannis, Alexios-Paul; Lee, Jerry C.; Beaud, Paul; et al. (2000)
    Flow, Turbulence and Combustion
  • Comparison of Direct and Large Eddy Simulations of the Turbulent Flow in a Valve/Piston Assembly
    Item type: Journal Article
    Montorfano, Andrea; Piscaglia, Federico; Schmitt, Martin; et al. (2015)
    Flow, Turbulence and Combustion
  • Multi-cycle Direct Numerical Simulations of a Laboratory Scale Engine: Evolution of Boundary Layers and Wall Heat Flux
    Item type: Journal Article
    Danciu, Bogdan A.; Giannakopoulos, George K.; Bode, Mathis; et al. (2025)
    Flow, Turbulence and Combustion
    Multi-cycle direct numerical simulations (DNS) of a laboratory-scale engine at technically relevant engine speeds (1500 and 2500 rpm) are performed to investigate the transient velocity and thermal boundary layers (BL) as well as the wall heat flux during the compression stroke under motored operation. The time-varying wall-bounded flow is characterized by a large-scale tumble vortex, which generates vortical structures as the flow rolls off the cylinder wall. The bulk flow is found to strongly affect the development of the BL pro-files, especially at higher engine speeds. As a result, the large-scale flow structures lead to alternating pressure gradients near the wall, invalidating the flow equilibrium assumptions used in typical wall modeling approaches. The thickness of the velocity BL and of the viscous sublayer was found to scale inversely with engine speed and crank angle. The thermal BL thickness also scales inversely with engine speed but increases with in-cylinder temperature. In contrast, thermal displacement thickness, which is sometimes used as a proxy for thermal BL thickness, was found to decrease with increasing temperature in the bulk.Examination of the heat flux distribution revealed areas of increased heat flux, particularly at places characterized by strong flow directed towards the wall. In addition, significant cyclic variations in the surface-averaged wall heat flux were observed for both engine speeds. An analysis of the cyclic tumble ratio revealed that the cycles with lower tumble ratio values near top dead center (TDC), indicative of an earlier tumble breakdown, also exhibit higher surface averaged wall heat fluxes. These findings extend previous numerical and experimental results for the evolution of BL structure during the compression stroke and serve as an important step for future engine simulations under realistic operating conditions.
  • Modeling Gas Flows in Packed Beds with the Lattice Boltzmann Method: Validation Against Experiments
    Item type: Journal Article
    Neeraj, Tanya; Velten, Christin; Janiga, Gabor; et al. (2023)
    Flow, Turbulence and Combustion
    This study aims to validate the lattice Boltzmann method and assess its ability to accurately describe the behavior of gaseous flows in packed beds. To that end, simulations of a model packed bed reactor, corresponding to an experimental bench, are conducted, and the results are directly compared with experimental data obtained by particle image velocimetry measurements. It is found that the lattice Boltzmann solver exhibits very good agreement with experimental measurements. Then, the numerical solver is further used to analyze the effect of the number of packing layers on the flow structure and to determine the minimum bed height above which the changes in flow structure become insignificant. Finally, flow fluctuations in time are discussed. The findings of this study provide valuable insights into the behavior of the gas flow in packed bed reactors, opening the door for further investigations involving additionally chemical reactions, as found in many practical applications.
  • Dynamic Evaluation of Mesh Resolution and Its Application in Hybrid LES/RANS Methods
    Item type: Journal Article
    Xiao, Heng; Wang, Jianxun; Jenny, Patrick (2014)
    Flow, Turbulence and Combustion
    In this work, we investigate a resolution evaluation criterion based on the ratio between turbulent length-scales and grid spacing within the context of dynamic resolution evaluation in hybrid LES/RANS simulations. A modified version of the commonly used length-scale criterion is adopted. The modified length-scale criterion is evaluated for a plane channel flow and compared to the criterion based on two-point correlations. Simulation results show qualitative agreement between the two criteria and physical predictions from both resolution indicators. These observations are confirmed by simulations of flows over periodic hills. It is further demonstrated that the length-scale based criterion is relatively less sensitive on variation of model parameters compared to criteria based on resolved percentage of turbulent quantities. The improved resolution criterion is applied in a dual-mesh hybrid LES/RANS solver. Numerical simulations with the hybrid solver suggest that the interactions between the length-scale resolution indicator and the solution are moderate, and that favorable comparisons with benchmark results are obtained. In summary, we demonstrate that the modified length-scale based resolution indicator performs satisfactorily in both pure LES and hybrid simulations. Therefore, it is selected as a promising candidate to provide reliable predictions of resolution adequacy for individual cells in hybrid LES/RANS simulations.
  • Large Eddy Simulation of a Reacting Kerosene Spray in Hot Vitiated Cross-Flow
    Item type: Journal Article
    Fredrich, Daniel; Miniero, Luigi; Pandey, Khushboo; et al. (2022)
    Flow, Turbulence and Combustion
    The evaporation and combustion characteristics of a kerosene spray injected perpendicularly into a cross-flow of high-temperature vitiated air is investigated. This fundamental flow configuration has wider implications for the future development of ultra-low emission aeronautical combustors, particularly with respect to technologies involving MILD combustion. Large eddy simulations with a Eulerian-Lagrangian framework are performed to investigate the spray evolution and the characteristics of the reaction zone for a range of conditions. For the closure of turbulence-chemistry interactions at the sub-grid scales, a transported probability density function approach solved by the Eulerian stochastic fields method is applied. A configuration based on the use of airblast atomisation is assessed first and compared with experimental observations. The effect of the atomiser air-to-liquid mass flow ratio is studied in greater detail, both in terms of the resulting gas-phase properties and the droplet evaporation process. Then, the effect of ambient pressure on the global spray flame behaviour is examined. For this part of the study, no atomising air is included in the simulation to separate the effects of ambient pressure on the spray from the interaction with the air jet. Analysis of the flame and spray properties at cross-flow operating pressures of 1 atm, 2 bar and 4 bar highlights the strong coupling between the reacting flow and droplet evaporation characteristics, which are highly affected by the penetration of the spray into a flow field characterised by relatively large gradients of temperature. The results reported in this work provide fundamental understanding for the development of novel low-emission combustion technologies and demonstrate the feasibility of applying large eddy simulation with detailed chemistry for the investigation of reacting aviation fuel sprays in hot vitiated cross-flow.
Publications 1 - 10 of 25