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  • Other Sources  (18)
  • 1
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    Numerical studies of the deposition of material released from fixed and rotary wing aircraft (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The computer code AGDISP (AGricultural DISPersal) has been developed to predict the deposition of material released from fixed and rotary wing aircraft in a single-pass, computationally efficient manner. The formulation of the code is novel in that the mean particle trajectory and the variance about the mean resulting from turbulent fluid fluctuations are simultaneously predicted. The code presently includes the capability of assessing the influence of neutral atmospheric conditions, inviscid wake vortices, particle evaporation, plant canopy and terrain on the deposition pattern. In this report, the equations governing the motion of aerially released particles are developed, including a description of the evaporation model used. A series of case studies, using AGDISP, are included.
    Keywords: AERODYNAMICS
    Type: NAS 1.26:3779 , NASA-CR-3779
    Format: application/pdf
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  • 2
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    Computer program for prediction of the deposition of material released from fixed and rotary wing aircraft (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This is a user manual for the computer code ""AGDISP'' (AGricultural DISPersal) which has been developed to predict the deposition of material released from fixed and rotary wing aircraft in a single-pass, computationally efficient manner. The formulation of the code is novel in that the mean particle trajectory and the variance about the mean resulting from turbulent fluid fluctuations are simultaneously predicted. The code presently includes the capability of assessing the influence of neutral atmospheric conditions, inviscid wake vortices, particle evaporation, plant canopy and terrain on the deposition pattern.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3780 , NAS 1.26:3780
    Format: application/pdf
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  • 3
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    Computing aerodynamic sound using advanced statistical turbulence theories (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: It is noted that the calculation of turbulence-generated aerodynamic sound requires knowledge of the spatial and temporal variation of Q sub ij (xi sub k, tau), the two-point, two-time turbulent velocity correlations. A technique is presented to obtain an approximate form of these correlations based on closure of the Reynolds stress equations by modeling of higher order terms. The governing equations for Q sub ij are first developed for a general flow. The case of homogeneous, stationary turbulence in a unidirectional constant shear mean flow is then assumed. The required closure form for Q sub ij is selected which is capable of qualitatively reproducing experimentally observed behavior. This form contains separation time dependent scale factors as parameters and depends explicitly on spatial separation. The approximate forms of Q sub ij are used in the differential equations and integral moments are taken over the spatial domain. The velocity correlations are used in the Lighthill theory of aerodynamic sound by assuming normal joint probability.
    Keywords: ACOUSTICS
    Type: NASA-CR-165697
    Format: application/pdf
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  • 4
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    Model predictions of wind and turbulence profiles associated with an ensemble of aircraft accidents (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The feasibility of predicting conditions under which wind/turbulence environments hazardous to aviation operations exist is studied by examining a number of different accidents in detail. A model of turbulent flow in the atmospheric boundary layer is used to reconstruct wind and turbulence profiles which may have existed at low altitudes at the time of the accidents. The predictions are consistent with available flight recorder data, but neither the input boundary conditions nor the flight recorder observations are sufficiently precise for these studies to be interpreted as verification tests of the model predictions.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-CR-2884 , M-225
    Format: application/pdf
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  • 5
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    Viscous effects in aircraft trailing vortices (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The mechanism of merging of like-signed aircraft vortices leading to a rapid redistribution of trailed vorticity in a wake through both convective and turbulent processes was investigated. Research was done experimentally in a small wind tunnel and analytically through the use of a code which computes turbulent transport using a second-order closure turbulent model. Computations are reported which demonstrate the merging phenomenon, and comparisons are made with experimental results. The usefulness of point vortex computations in predicting merging was explored. Limited computations showed that jet exhaust does not appreciably alter the merging phenomenon. The effect of ambient atmospheric turbulence on the aging of an aircraft wake was investigated at a constant turbulent dissipation rate. It was shown that under stable atmospheric conditions, when atmospheric macroscales are less than or equal to the vortex spacing, misleading results may be obtained.
    Keywords: AERODYNAMICS
    Type: NASA, Washington Wake Vortex Minimization; p 61-128
    Format: application/pdf
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  • 6
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    Turbulent transport model of wind shear in thunderstorm gust fronts and warm fronts (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A model of turbulent flow in the atmospheric boundary layer was used to simulate the low-level wind and turbulence profiles associated with both local thunderstorm gust fronts and synoptic-scale warm fronts. Dimensional analyses of both type fronts provided the physical scaling necessary to permit normalized simulations to represent fronts for any temperature jump. The sensitivity of the thunderstorm gust front to five different dimensionless parameters as well as a change from axisymmetric to planar geometry was examined. The sensitivity of the warm front to variations in the Rossby number was examined. Results of the simulations are discussed in terms of the conditions which lead to wind shears which are likely to be most hazardous for aircraft operations.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-CR-3002 , ARAP-327
    Format: application/pdf
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  • 7
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    Atmospheric-wake vortex interactions (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The interactions of a vortex wake with a turbulent stratified atmosphere are investigated with the computer code WAKE. It is shown that atmospheric shear, turbulence, and stratification can provide the dominant mechanisms by which vortex wakes decay. Computations included the interaction of a vortex wake with a viscous ground plane. The observed phenomenon of vortex bounce is explained in terms of secondary vorticity produced on the ground. This vorticity is swept off the ground and advected about the vortex pair, thereby altering the classic hyperbolic trajectory. The phenomenon of the solitary vortex is explained as an interaction of a vortex with crosswind shear. Here, the vortex having the sign opposite that of the sign of the vorticity in the shear is dispersed by a convective instability. This instability results in the rapid production of turbulence which in turn disperses the smoke marking the vortex.
    Keywords: AERODYNAMICS
    Type: NASA-CR-145336 , ARAP-331
    Format: application/pdf
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  • 8
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    Turbulent transport model of a thunderstorm gust front (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A second-order closure turbulent model is adopted to predict complex fluid flows; few a priori assumptions about the internal turbulent and mean flow structures are required. The flow simulations are applied to the analysis of local gust fronts generated by rain-cooled outflows from severe thunderstorms. Results of the simulations provide a means for discussing the behavior of an aircraft passing through a thunderstorm-related downdraft.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Conference on Severe Local Storms; Oct 18, 1977 - Oct 21, 1977; Omaha, NE
    Format: text
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  • 9
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    The role of atmospheric shear, turbulence and a ground plane on the dissipation of aircraft vortex wakes (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Enhanced dispersion of two-dimensional trailed vortex pairs within simplified neutral atmospheric backgrounds is studied numerically for three conditions: when the pair is imbedded in a constant turbulent bath (constant dissipation); when the pair is subjected to a mean cross-wind shear; and when the pair is near the ground. Turbulent transport is modeled using second-order closure turbulent transport theory. The turbulent background fields are constructed using a superequilibrium approximation. The computed results allow several general conclusions to be drawn with regard to the reduction in circulation of the vortex pair and the rolling moment induced on a following aircraft: (1) the rate of decay of a vortex pair increases with increasing background dissipation rate; (2) cross-wind shear disperses the vortex whose vorticity is opposite to the background; and (3) the proximity of a ground plane reduces the hazard of the pair by scrubbing. The phenomenon of vortex bounce is explained in terms of secondary vorticity produced at the ground plane. Qualitative comparisons are made with available experimental data, and inferences of these results upon the persistence of aircraft trailing vortices are discussed.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 78-110 , Aerospace Sciences Meeting; Jan 16, 1978 - Jan 18, 1978; Huntsville, AL
    Format: text
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  • 10
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    Atmospheric pollutant dispersion using second order closure modeling of the turbulence (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Keywords: ENVIRONMENT POLLUTION
    Type: EPA Proc. of the Conf. on Environ. Modeling and Simulation; p 714-718
    Format: text
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