David C. Burnham

Decay Characteristics of Wake Vortices from Jet Transport Aircraft

In the 1970s the B-747-100 alleviation tests, sponsored by NASA with FAA participation, provided unique continuous-wave lidar data, in which the vortex cores could be measured because they were marked with smoke. Measurements for both normal and alleviated wakes showed that the vortex core is persistent whereas the outer circulation of the vortex decays. This form of decay is exactly the opposite of what is observed at low Reynolds number for small aircraft or in wind tunnels. The stability of the core is consistent with the essentially laminar core observed via flow visualization. The circulation profile for the normal wake is well fitted by the Burnham-Hallock model both after initial rollup and after significant decay of the total circulation. The core size for the normal B-747-100 wake is larger (5% of wingspan) than typically observed for aircraft with zero or two wing-mounted engines. The observed wake decay means that the total vortex circulation is approximately equal to the popular vortex strengt...

Measurements of Wake Vortices Interacting with the Ground

Although wake vortices are known to decay more rapidly near the ground than away from the ground, the details of the ground interaction are not well understood. Propeller anemometer arrays located under the approach path have been used to study vortex transport and provide some information about the vortex interaction with the ground, such as the generation of secondary vortices via boundary-layer detachment. A propeller anemometer array at John F. Kennedy International Airport using 8.5-m poles was augmented with 1) a sonic anemometer measuring three-dimensional wind and temperature at 10 Hz and 2) a vertical array of vertical wind and crosswind anemometers, mounted at four additional levels (4.2, 3.2, 1.05, and 0.5 m). The sonic anemometer gave 1) measurements of turbulence inside the vortex flowfield and 2) indications of vertical variations in the ambient headwind and temperature, which were brought down to the measurement level by the descent of the vortex recirculation oval. In general, under conditions of low to moderate turbulence, the turbulence level inside the wake vortex flowfield is greater than that in the ambient wind. The vertical anemometer array showed that the crosswind profile under a wake vortex in ground effect has a very thin boundary layer, much thinner than that of the ambient wind. It also provided some details concerning the wind profile of the secondary vortex.

Robust Low Cost Airport Wake Vortex Sensor

A conventional Radar Acoustic Sounding System atmospheric proe ler has been converted into a wake vortex sensor that can detect, track, and measure aircraft wake vortices under all weatherconditions. The resulting wake vortex sensor has been operated automatically with real-time processing at New York’ s Kennedy International Airport,wherewakesfromaircraftinallweightclassesweredetected.Comparisonswithotherwakevortexsensors are presented and show consistent vortex tracking with a very low false alarm rate. Possible applications of the sensor to wake vortex avoidance systems are discussed. I. Introduction A IRCRAFT wake vortices may be dangerous to following aircraftduringlandingandtakeoff.Sincetheadventofjumbojets in the 1970s, the Federal Aviation Administration (FAA) imposed three- to six-mile minimum spacings between leader and follower aircraft, depending on aircraft weight category. These spacings are overly conservative most of the time, causing airport delays and reduced capacity, particularly in bad weather. Based on simulations, 1 the FAAhas projected airlinesavings of

WAKE TURBULENCE LIMITS ON PAIRED APPROACHES TO PARALLEL RUNWAYS

5billion a yearif spacings could be safely reduced by 30 s during high airport trafe c periods (because vortices often decay quickly or are rapidly moved out of the glide path by crosswinds ).