Igor N. Smalikho

Characterization of Aircraft Wake Vortices by 2-μm Pulsed Doppler Lidar

Abstract The 2-μm pulsed Doppler lidar, already successfully used for wind and turbulence measurements, has been modified for long-range wake-vortex characterization. In particular, a four-stage data processing algorithm has been developed to achieve precise profiles of tangential velocities from which the vortex parameters such as trajectories, core separation, tilt angle, and circulation can be derived. The main advantage of the pulsed lidar is its long-range capability of more than 1 km. This allows for observations over long periods from the moment of wake generation to a progressed state of vortex decay. With the field experiment at Tarbes airfield the potential of the 2-μm pulsed Doppler lidar for full-scale wake-vortex characterization has been demonstrated. Two examples showing the parameters of wake vortices generated by large transport aircraft (LTA)-type aircraft will be presented.

Measurement of Atmospheric Turbulence by 2-μm Doppler Lidar

Abstract Two methods for the estimation of the turbulence energy dissipation rate (TEDR) from data measured by a 2-μm coherent Doppler lidar are described in this paper. Based on data measured at the Tarbes-Lourdes-Pyrenees International Airport in summer 2003, height profiles of TEDR have been retrieved. The results of TEDR estimation both from the Doppler spectrum width and from the velocity structure function are compared. Moreover, the experiment has been treated by numerical simulation and the theoretical results have been used for verification of the described methods.

Techniques of Wind Vector Estimation from Data Measured with a Scanning Coherent Doppler Lidar

Abstract The results of a theoretical study of the feasibility of wind velocity vector estimation from data, measured with a scanning coherent Doppler lidar, are presented. The estimation techniques considered are (a) the direct sine wave fitting (DSWF) and the filtered sine wave fitting (FSWF), where at first the radial wind velocities are estimated and then the wind vector is estimated from the dependence of the radial velocity versus the azimuth angle of the scanning; and (b) the maximum of the function of accumulated spectra (MFAS) and the maximum likelihood for the wind vector estimation (WV ML), where the wind vector is estimated directly from data measured by a scanning lidar without intermediate estimation of the radial wind velocities. It has been shown that due to strong averaging of noise fluctuations in accumulated spectra, the WV ML and MFAS techniques allow one to estimate the wind vector with acceptable accuracy at an essentially lower signal-to-noise ratio (SNR) than the methods of the sin...

Representativeness of wind measurements with a cw Doppler lidar in the atmospheric boundary layer.

The representativity problem of laser Doppler anemometer wind measurements in the boundary layer under different atmospheric conditions has been investigated theoretically and experimentally. The calculations of the mean wind-velocity measurement errors for the surface layer under different types of thermal stratification and for the boundary layer under neutral conditions have been carried out. The theoretical conclusions are confirmed by the experimental results.

Comparison of wake-vortex parameters measured by pulsed and continuous-wave lidars

Field trials carried out at Tarbes airfield in the summer of 2002 offered the unique opportunity to compare the results of simultaneous wake-vortex measurements by the 2-µm pulsed Doppler lidar from DLR, German Aerospace Research Center, and the 10-µm continuous wave (cw) Doppler lidars from ONERA and QinetiQ. The discrepancies in vortex core position obtained from the data of the pulsed lidar and the cw lidars are 9 m for the vertical and 13 m for the horizontal co-ordinates. The accuracies of the vortex circulation measurements with the DLR and ONERA lidars are almost the same and equal 13 m 2 /s. This accuracy and the long-range capability of the pulsed lidar allows precise measurements over long periods from the moment of wake generation to a progressed state of vortex decay. Moreover, the influence of different atmospheric turbulence conditions and aircraft configurations on the wake-vortex circulation can be analyzed. This has been demonstrated out of ground effect under conditions of weak to moderate levels of turbulence.

Measurements of Turbulent Energy Dissipation Rate with a CW Doppler Lidar in the Atmospheric Boundary Layer

Abstract The results of a theoretical and experimental study of the feasibility of the turbulent energy dissipation rate ϵT measurements with a continuous wave (CW) CO2 Doppler lidar in the atmospheric boundary layer are presented. Three methods of probing ϵT are considered: 1) Doppler spectrum width, 2) the temporal spectrum (temporal structure function) of wind velocity measured by the Doppler lidar, and 3) spatial structure function. In these methods, information on the dissipation rate is extracted by means of analysis of the corresponding statistical characteristics of wind velocity in the inertial subrange of the turbulence, taking into account the spatial averaging of the measured wind velocity fluctuations over sounded volume. In the first and third methods, the spatial structure of the turbulence is analyzed directly. In the second method, to determine ϵT from the measured temporal characteristics, it is necessary to use a model for the spatiotemporal correlation function of wind velocity. As a r...

Characterization of Aircraft Wake Vortices by Airborne Coherent Doppler Lidar

This paper presents a new method of wake-vortex characterization by using the 2-μm coherent Doppler lidar in airborne configuration. After modification of the scanning and data acquisition tools, the lidar system has been integrated in the DLR research aircraft Falcon 20. For wake-vortex generation a second DLR aircraft, the Advanced Technologies Testing Aircraft System equipped with a smoke generator on the portside wing, was used. Different scanning modes and flight strategies have been investigated and tested during three tryout flights. Results of vortex trajectories and circulation strengths, measured in the upper part of and above the atmospheric boundary layer, are presented. Based on the results of the tryout flights, the potential of this method for characterization of wake vortices from large transport aircraft equipped with smoke generators is estimated.

Calculation of the backscatter amplification coefficient of laser radiation propagating in a turbulent atmosphere using numerical simulation

A numerical simulation-based algorithm is proposed for calculating the backscatter amplification (BSA) coefficient of laser radiation propagating in a turbulent atmosphere. The algorithm permits one to obtain results for conditions under which the known analytical calculation methods are inapplicable. Using this algorithm, the BSA coefficient is analyzed numerically for different conditions of laser radiation propagation in the atmosphere.

Aircraft Wake Vortex Measurement with Airborne Coherent Doppler Lidar

An experiment for airborne Doppler lidar measurement of wake vortices generated by a large transport aircraft in the free atmosphere has been successfully carried out. In this paper, the description of the experiment, data processing procedure, and measurement results are given. It was shown that the use of smoke generators placed on large transport aircraft wings allows some high-quality wake vortex measurements with 2 μm coherent Doppler lidar installed in a second aircraft.

Characterization of Aircraft Wake Vortices by Multiple-Lidar Triangulation

Three continuous-wave lidar systems have been deployed to measure simultaneously the aire ow associated with wake vortices generated by a medium-size full-scale test aircraft. The lidar systems were positioned to permit investigation of fundamental aspects of vortex behavior. Two lidars were located 27 m apart, along a line parallel to the glide slope. This allowed a consistency check via comparison of the two sets of results and gave an indication of axial variations in vortex location and character. The third lidar was positioned 80 m away along a line perpendicular to the glide slope. This permitted accurate location of the vortex cores by triangulation methods via a tracking algorithm based on an extended Kalman e lter, typically to an accuracy of better than § §4.0 m. The mean value of core separation for a vortex age of 2 s agrees to within 5% of that predicted for this aircraft using the approximation of elliptically distributed lift. Calculation of vortex circulation requires accurate information on vortex range in conjunction with tangent velocity proe les: The trajectories thus determined are an essential input, and, hence, this method will reduce the uncertainty in the values of circulation in comparison to studies involving only a single lidar.