Large Eddy Simulation of Aircraft Wake Vortices in a Homogeneous Atmospheric Turbulence: Vortex Decay and Descent

The effects of ambient turbulence on decay and descent of aircraft wake vortices are studied using a validated, three-dimensional, large-eddy simulation model. Numerical simulations are performed in order to isolate the effect of ambient turbulence on the wake vortex decay rate within a neutrally-stratified atmosphere. Simulations are conducted for a range of turbulence intensities, by injecting wake vortex pairs into an approximately homogeneous and isotropic turbulence field. The decay rate of the vortex circulation increases clearly with increasing ambient turbulence level, which is consistent with field observations. Based on the results from the numerical simulations, simple decay models are proposed as functions of dimensionless ambient turbulence intensity (n) and demisnionless time (T) for the circulation averaged over a range of radial distances. With good agreement with the numerical results, a Gaussian type of vortex decay model is proposed for weak turbulence, while an exponential type of vortex decay model can be applied for strong turbulence. A relationship for the vortex descent based on above vortex decay model is also proposed. Although the proposed models are based on simulations assuming neutral stratification, the model predictions are compared to Lidar vortex measurements observed during stable, neutral, and unstable atmospheric conditions. In the neutral and unstable atmospere, the model predictions appear to be in reasonable agreement with the observational data, while in the stably-stratified atmosphere, they largely underestimate the observed circulation decay with consistent overestimation of the observed vortex descent. The underestimation of vortex decay during stably-stratified conditions suggests that stratification has an important influence on vortex decay when ambient levels of turbulence are weak.

[1]  S. Arya,et al.  Large Eddy Simulation of Aircraft Wake Vortices: Atmospheric Turbulence Effects , 1997 .

[2]  Philippe R. Spalart.  Airplane trailing vortices , 2000 .

[3]  Robert E. Robins,et al.  Development and validation of a wake vortex predictor algorithm , 1998 .

[4]  David A. Hinton,et al.  NASA Wake Vortex Research for Aircraft Spacing , 1997 .

[5]  Turgut Sarpkaya,et al.  Effect of ambient turbulence on trailing vortices , 1987 .

[6]  L. Rayleigh.  On the Dynamics of Revolving Fluids , 1917 .

[7]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[8]  Turgut Sarpkaya,et al.  Effect of ambient turbulence on trailing vortices , 1987 .

[9]  Coleman duP. Donaldson,et al.  Vortex Wakes of Conventional Aircraft , 1975 .

[10]  D. Burnham,et al.  Decay characteristics of wake vortices from jet transport aircraft , 1997 .

[11]  Ivar Tombach,et al.  Observations of Atmospheric Effects on Vortex Wake Behavior , 1973 .

[12]  David S. DeCroix,et al.  Toward three-dimensional modeling of a wake vortex pair in the turbulent planetary boundary layer , 1997 .

[13]  T. Sarpkaya.  Decay of wake vortices of large aircraft , 1998 .

[14]  D C Burnham,et al.  Chicago Monostatic Acoustic Vortex Sensing System. Volume IV. Wake Vortex Decay. , 1982 .

[15]  Fred H. Proctor,et al.  Numerical Simulation of Wake Vortices Measured During the Idaho Falls and Memphis Field Programs , 1996 .

[16]  H.-T. Liu,et al.  Effects of ambient turbulence on the decay of a trailing vortex wake , 1992 .

[17]  R Tatnall Christopher,et al.  An Investigation of Candidate Sensor-Observable Wake Vortex Strength Parameters for the NASA Aircraft Vortex Spacing System (AVOSS) , 1998 .

[18]  A Hinton David,et al.  A Candidate Wake Vortex Strength Definition for Application to the NASA Aircraft Vortex Spacing System (AVOSS) , 1997 .

[19]  A. Kolmogorov.  The local structure of turbulence in incompressible viscous fluid for very large Reynolds numbers , 1991, Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences.

[20]  M. E. Teske,et al.  Neutral Atmospheric Effects on the Dissipation of Aircraft Vortex Wakes , 1978 .

[21]  Fred H. Proctor,et al.  The NASA-Langley Wake Vortex Modelling Effort in Support of an Operational Aircraft Spacing System , 1998 .

[22]  Steven D. Campbell,et al.  Wake Vortex Field Measurement Program at Memphis, Tennessee: Data Guide , 1997 .

[23]  G. C. Greene,et al.  An approximate model of vortex decay in the atmosphere , 1985 .

[24]  Caskey,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS I . THE BASIC EXPERIMENT , 1962 .

[25]  Turgut Sarpkaya,et al.  Trailing vortices in homogeneous and density-stratified media , 1983, Journal of Fluid Mechanics.

[26]  E. R. Bate,et al.  Lifespan of trailing vortices in a turbulent atmosphere , 1976 .

[27]  D. A. Hinton,et al.  Two Dimensional Wake Vortex Simulations in the Atmosphere: Preliminary Sensitivity Studies , 1997 .

[28]  Denis Darracq,et al.  Three-dimensional Large Eddy Simulation of Wake Vortices. Comparison with Field Measurements. , 1997 .

[29]  F. H. Proctor,et al.  The terminal area simulation system. Volume 1: Theoretical formulation , 1987 .

[30]  S. Crow.  Stability theory for a pair of trailing vortices , 1970 .