scholarly journals A Large-Eddy Simulation Study of Contrail Ice Number Formation

2020 ◽  
Vol 77 (7) ◽  
pp. 2585-2604
Author(s):  
David C. Lewellen
Keyword(s):  
Aircraft Engine ◽  
Climate Impact ◽  
Box Model ◽  
Droplet Growth ◽  
Temporal Representation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Analytic Models ◽  
Ultrafine Aerosol ◽  
Engine Size

AbstractIce crystal number is a critical ingredient in the potential climate impact of persistent contrails and contrail-induced cirrus. We perform an extensive set of large-eddy simulations (LES) of ice nucleation and growth within aircraft exhaust jets with an emphasis on assessing the importance of detailed plume mixing on the effective ice-number emission index (EIiceno) produced for different conditions. Parameter variations considered include ambient temperature, pressure, and humidity; initial aerosol origin (exhaust or ambient), number, and properties; and aircraft engine size. The LES are performed in a temporal representation with binned microphysics including the basics of activation of underlying aerosol, droplet growth, and freezing. We find that a box-model approach reproduces EIiceno from LES well for sufficiently low aerosol numbers or when crystal production is predominantly on ambient aerosol. For larger exhaust aerosol number the box model generally overestimates EIiceno and can underestimate the fraction from ultrafine aerosol. The effects of different parameters on EIiceno can largely be understood with simpler analytic models that are formulated in low and high aerosol-number limits. The simulations highlight the potential importance of “cold” contrails, ambient ultrafine aerosols, crystal loss due to competition between different-sized crystals, and limitations on reducing EIiceno. We find EIiceno insensitive to engine size for lower aerosol numbers, but decreasing with increasing engine size for higher aerosol numbers. Temporal versus spatial representations for jet LES are compared in an appendix.

Reynolds Study of the Flow Induced Noise

2011 ◽  
Vol 110-116 ◽  
pp. 4615-4622
Author(s):  
Deepesh Kumar Singh ◽  
G. Bandhyopadhyay
Keyword(s):  
Circular Cross Section ◽  
Aircraft Engine ◽  
Broadband Noise ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Noise Emission ◽  
Cross Sectional ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Induced Noise

2D Large Eddy Simulation turbulence model coupled with Ffowcs-Williams-Hawkins model and Boundary Element Method is used to perform a study of the effect of the Reynolds number on the broadband noise emitted due to the incompressible fluid structure interaction. The method is then used to calculate the broadband noise emitted by the aerodynamic flow over different shape bodies having same cross-sectional area with the intent to know the most suitable cross sectional geometry of the fuel manifolds in the aircraft engine afterburner in terms of minimum noise emission. The results obtained suggests that a 5dB benefit in sound emission could be obtained by the halving the diameter of the circular cross-section used for the fuel manifolds, to make them elliptical keeping cross sectional area constant.

Large Eddy Simulation of Turbulent Combustion Flow in a Gas-Turbine Combustor

2003 ◽  
Author(s):  
Nobuyuki Taniguchi ◽  
Takuji Tominaga ◽  
Akiyoshi Hashimoto ◽  
Yuichi Itoh
Keyword(s):  
Large Eddy Simulation ◽  
Gas Turbine ◽  
Turbulent Flows ◽  
Aircraft Engine ◽  
Gas Turbine Combustor ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Combustion Flow ◽  
Energy Equipment ◽  
Primary Problem

In views of mechanical engineering, a primary problem in energy equipment design is to control of turbulent flows. Large eddy simulation is applied for analyzing tree-dimensional and unsteady features in gas-turbine combustor. For these purpose, LES with a G-equation flame model based on the flamelet concept is developed on the general co-ordinate grid and is demonstrated in design of a premixed gas-turbine combustor for aircraft engine. The simulations of the flame propagation are executed in some conditions with different relations of the equivalent ratios, and the flame positions and propagating behaviors are analyzed.

scholarly journals An Evaluation of Size-Resolved Cloud Microphysics Scheme Numerics for Use with Radar Observations. Part I: Collision–Coalescence

2019 ◽  
Vol 76 (1) ◽  
pp. 247-263 ◽  
Author(s):  
Hyunho Lee ◽  
Ann M. Fridlind ◽  
Andrew S. Ackerman
Keyword(s):  
Cloud Microphysics ◽  
Box Model ◽  
Computationally Efficient ◽  
Microphysics Scheme ◽  
Numerical Diffusion ◽  
Radar Observations ◽  
Simulation Fidelity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Bin Microphysics

Abstract This study evaluates some available schemes designed to solve the stochastic collection equation (SCE) for collision–coalescence of hydrometeors using a size-resolved (bin) microphysics approach and documents their numerical properties within the framework of a box model. Comparing three widely used SCE schemes, we find that all converge to almost identical solutions at sufficiently fine mass grids. However, one scheme converges far slower than the other two and shows pronounced numerical diffusion at the large-drop tail of the size distribution. One of the remaining two schemes is recommended on the basis that it is well converged on a relatively coarse mass grid, stable for large time steps, strictly mass conservative, and computationally efficient. To examine the effects of SCE scheme choice on simulating clouds and precipitation, two of the three schemes are compared in large-eddy simulations of a drizzling stratocumulus field. A forward simulator that produces Doppler spectra from the large-eddy simulation results is used to compare the model output directly with radar observations. The scheme with pronounced numerical diffusion predicts excessively large mean Doppler velocities and overly broad and negatively skewed spectra compared with observations, consistent with numerical diffusion demonstrated in the box model. Statistics obtained using the recommended scheme are closer to observations, but notable differences remain, indicating that factors other than SCE scheme accuracy are limiting simulation fidelity.

scholarly journals The Contrail Mitigation Potential of Aircraft Formation Flight Derived from High-Resolution Simulations

Aerospace ◽  
2020 ◽  
Vol 7 (12) ◽  
pp. 170 ◽  
Author(s):  
Simon Unterstrasser
Keyword(s):  
Water Vapour ◽  
Climate Impact ◽  
Formation Flight ◽  
Large Set ◽  
Climate Effect ◽  
Mitigation Potential ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Close Proximity

Formation flight is one potential measure to increase the efficiency of aviation. Flying in the upwash region of an aircraft’s wake vortex field is aerodynamically advantageous. It saves fuel and concomitantly reduces the carbon foot print. However, CO2 emissions are only one contribution to the aviation climate impact among several others (contrails, emission of H2O and NOx). In this study, we employ an established large eddy simulation model with a fully coupled particle-based ice microphysics code and simulate the evolution of contrails that were produced behind formations of two aircraft. For a large set of atmospheric scenarios, these contrails are compared to contrails behind single aircraft. In general, contrails grow and spread by the uptake of atmospheric water vapour. When contrails are produced in close proximity (as in the formation scenario), they compete for the available water vapour and mutually inhibit their growth. The simulations demonstrate that the contrail ice mass and total extinction behind a two-aircraft formation are substantially smaller than for a corresponding case with two separate aircraft and contrails. Hence, this first study suggests that establishing formation flight may strongly reduce the contrail climate effect.

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