Michael Frech

Wake Vortices in Convective Boundary Layer and Their Influence on Following Aircraft

The decay of three wake vortex pairs of a B-747 aircraft in an evolving and convectively driven atmospheric boundary layer is investigated by means of large-eddy simulations (LES). Convective boundary layers are considered hazardousbecausetheupdraft velocitiesofa thermalmay compensatetheinduceddescent speed ofthevortex pair such that the vortices stall in the e ight path. The LES results illustrate that 1 )the primary rectilinear vortices are rapidly deformed on the scale of alternating updraft and downdraft regions; 2 ) parts of the vortices stay on e ight level but are quickly eroded by the turbulence of the updraft; 3 )the longest living sections of the vortices are foundinregionsofrelativelycalmdownwarde ow,which augmentstheirdescent.Striptheory calculationsareused to illustrate the temporal and spatial development of lift and rolling moments experienced by a following medium weight class B-737 aircraft. Characteristics of the respective distributions are analyzed. Initially, the maximum rolling moments slightly exceed theavailableroll controloftheB-737. After60 sthe probability ofrolling moments exceeding 50% of the roll control has decreased to 0.009% in a safety corridor around the glide path. Nomenclature b = aircraft span b0 = initial vortex spacing c = section chord cl = section lift coefe cient dP = probability difference g = gravitational acceleration k = wave number

High-Resolution Weather Database for the Terminal Area of Frankfurt Airport

Abstract A 1-yr meteorological dataset for the terminal area of Frankfurt Airport in Germany has been generated with a numerical weather prediction system to provide a synthetic though realistic database for the evaluation of new operational aircraft arrival procedures and their associated risks. The comparison of the 1-yr dataset with a local surface wind climatology indicates that the main climatological features are recovered. A subset of 40 days is validated against measurements from a sound detection and range/radio acoustic sounding system (SODAR/RASS) taken at Frankfurt Airport. The RMS errors of wind speed and direction are between 1.5 m s−1 at the surface and 2 m s−1 at 300 m and 40°, respectively. The frequency distribution of meteorological parameters, such as the wind component perpendicular to the glide path, shear, and thermal stratification, show good agreement with observations. The magnitude of the turbulent energy dissipation rate near the surface is systematically overestimated, whereas...

Skill of an Aircraft Wake-Vortex Model Using Weather Prediction and Observation

The performance of the two-phase probabilistic wake-vortex transport and decay model using numerical weather prediction and weather observations as input is analyzed using data from a wake measurement campaign carried out at Frankfurt airport during fall 2004. The wake-vortex observations include wakes evolving in and out of ground effects. The best forecast quality is achieved for wakes evolving in ground effect. We include the simplified hazardarea prediction model to compute the time to clear the corridor from hazardous wakes and to assess the potential capacity gain for single-runway operations. The highest-capacity potential can be expected when weather observations are employed for wake predictions. The limiting factor for capacity are wakes evolving in ground effect. Out of ground effect, the self-induced vertical transport of the wake vortex proves to be a robust mechanism to clear the approach corridor in an efficient way. This is found independently from the source of meteorological input. In contrast, the consideration of lateral wake transport alone leads to marginal-capacity potential. The analysis also shows that weather data along the glide path can be provided by numerical weather prediction for safe wake prediction.

Concept of Wake Vortex Behavior Classes

The concept of wake vortex behavior classes is introduced. Rather than consider the individual wake vortex evolution, diagnosis of the meteorological situation causing a characteristic wake vortex behavior is proposed. We define four wake vortex behavior classes that explicitly refer to both the wake vortex transport and the decay behavior. The statistical analysis of the Memphis wake vortex database supports this new concept and also shows the distinct influence of weather on wake vortex behavior. The analysis indicates that the high-level safety of International Civil Aviation Organization (ICAO) separations between consecutive aircraft is primarily due to the transport of wake vortices out of a flight corridor. It is found that, depending on atmospheric conditions, a significant fraction of wake vortices does not decay enough to satisfy the existing ICAO separations. Of these wake vortices, a small fraction is within a safety corridor and therefore poses a potential risk to a following aircraft. A simple crosswind criterion with a threshold of 2 m/s provides a safety corridor that is free of wake vortices under radar separation. This demonstrates the large potential for safe reduction of aircraft separation under crosswind conditions. This is supported by an analysis of a wind climatology representative for Frankfurt airport.

Short‐term prediction of the horizontal wind vector within a wake vortex warning system

A wake vortex warning system (WVWS) has been developed for Frankfurt Airport. This airport has two parallel runways which are separated by 518 m, a distance too short to operate them independently because wake vortices may be advected to the adjacent runway. The objective of the WVWS is to enable operation with reduced separation between two aircraft approaching the parallel runways during appropriate wind conditions. The WVWS applies a statistical persistence model to predict the crosswind within a 20-minute period. One of the main problems identified in the old WVWS is discontinuity between successive forecasts. These forecast breakdowns were not acceptable to air traffic controllers. At least part of the problem was related to the fact that the forecast was solely based on the prediction of crosswind. A new method is developed on the basis of 523 days of sonic anemometer measurements at Frankfurt Airport. It is demonstrated that the prediction of the horizontal wind vector avoids these difficulties and significantly improves the system’s performance.

Increased Arrival Capacity Through the Use of the ATC-Wake Separation Mode Planner

Today’s wake vortex separation rules tend to become capacity bottlenecks at busy airports. Within the ATC-Wake project for the European Commission, an integrated Air Traffic Control (ATC) wake vortex safety and capaci ty system has been designed so as to provide the means to significantly enhance airport capacity. The system will enable Air Traffic Controllers to apply new weather based dynamic aircraft separation. One of the components of the ATC-Wake system is the Separation Mode Planner (SMP) that advices the ATC supervisor about safe and adequate separation. The SMP is used in the planning phase where weather and wake vortex forecast information is used together with aircraft separation rules to establish the arrival and/or de parture sequence. Weather nowcasting and wake vortex prediction and detection information is used in the tactical phase to monitor and control safe separation. Wind forecast data alo ng the flight path is used in the proposed methodology of the SMP to determine time frames suitable for reduced separation. Criteria on crosswind and associated safe separation minima are derived from safety assessment results. The methodology is illustrated using Nowca sting Wake Vortex Impact Variables (NOWVIV) wind forecast data and WAke Vortex Induced Risk assessment (WAVIR) results for Single Runway Arrivals. Analysis of a crosswind climatology provides insight in the potential benefits in terms of runway throughput or delay reduction.