Fast-Time Modeling of Ground Effects on Wake Vortex Transport and Decay

Flow Turbulence Combust

Tchipev

Stephan

2016

Wall-resolved large eddy simulations are employed to investigate the behaviour of wake vortices and single vortices in ground proximity at a variety of wind conditions. The six considered strengths of wind, ranging between 0.5 and 4 times the initial wake vortex descent speed, w 0 , include practically and theoretically significant wind speeds. A crosswind of 0.5 w 0 may lead to windward stall posing a potential hazard to subsequently landing aircraft, whereas theoretical considerations predict that at 4 w 0 the rebound of the luff vortex is completely suppressed. The same range of wind speeds is also used to investigate the effects of headwind and diagonal wind in order to discriminate between effects of environmental turbulence increasing with wind speed and the direction of the wind shear. The study has been complemented by a number of single vortex computations in order to differentiate between effects related to the mutual interaction of the vortex pair and the individual vortices with the turbulent boundary layer flow. It is shown that vortex ascent, descent, rebound and decay characteristics are controlled by (i) the interaction of the vortices with secondary vorticity detaching from the ground, (ii) the redistribution of vorticity of the boundary layer which is altering the path of the primary vortices by mutual velocity induction, and (iii) the interaction of the vortices with the environmental turbulence.

Section: Crosswind Effects On Single Vortices and Vortex Pairsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Wind Impact on Single Vortices and Counterrotating Vortex Pairs in Ground Proximity

Flow Turbulence Combust

Tchipev

Stephan

2016

“…In addition, the vortices undergo complex interactions with the ground. Substantial effort has been made in the past to understand the governing physics of vortex dynamics [2][3][4][5][6][7][8] and to develop wakevortex prediction models [9][10][11][12][13][14][15][16][17] to enhance the capacity of the airspace while maintaining the safety.…”

mentioning

confidence: 99%

Multimodel Ensemble Methods for Prediction of Wake-Vortex Transport and Decay

Körner

Ahmad

et al. 2017

Journal of Aircraft

Several multimodel ensemble methods are selected and further developed to improve the deterministic and probabilistic prediction skills of individual wake-vortex transport and decay models. The different multimodel ensemble methods are introduced, and their suitability for wake applications is demonstrated. The selected methods include direct ensemble averaging, Bayesian model averaging, and Monte Carlo simulation. The different methodologies are evaluated employing data from wake-vortex field measurement campaigns conducted in the United States and Germany.= forecast of ith model g i yjf i = probability density function of forecast L = likelihood PB = probability that B occurs PBjA = probability that B occurs, given that A occurs py = probability density function of the y forecast

“…Various fast-time wake vortex models have been developed in the past to achieve a tactical capacity and safety gain [13][14][15][16][17][18][19][20]. These are simplified models, which are often trained with measurement data or LES output in order to calibrate the model forecasts.…”

mentioning

confidence: 99%

Multi-model ensemble wake vortex prediction

Körner

Aircraft Eng & Aerospace Tech

2016

Tag der mündlichen Prüfung: 25.07.2017 Diese Dissertation ist auf den Internetseiten der Universitätsbibliothek online verfügbar. Für meinen Großvater. v Eidesstattliche Erklärung Ich versichere hiermit an Eides Statt, dass ich die vorliegende Dissertation mit dem Titel "Multi-Model Ensemble Wake Vortex Prediction" selbstständig und ohne unzulässige fremde Hilfe erbracht habe. Ich habe keine anderen als die angegebenen Quellen und Hilfsmittel benutzt. Für den Fall, dass die Arbeit zusätzlich auf einem Datenträger eingereicht wird, erkläre ich, dass die schriftliche und die elektronische Form vollständigübereinstimmen. Die Arbeit hat in gleicher oderähnlicher Form noch keiner Prüfungsbehörde vorgelegen. Zudem versichere ich Eides statt, dass ich kein erfolgloses Promotionsverfahren bzw. Promotionsstudium zum Dr.-Ing/ Dr.rer.nat. durchgeführt habe. AbstractAs a response to lift, a complex flow pattern is shed from the wings of an aircraft that evolves into a pair of counter-rotating vortices. Their behavior is strongly influenced by the atmosphere and further underlies a complex interaction with the ground. Due to the rolling momentum that the vortices may induce and the forces that they can exert they pose a potential hazard to following air traffic, especially along the glide path and in ground proximity. To avoid dangerous incidents, separation regulations based on aircraft mass exist that is currently under revision in the context of RECAT. However, air traffic is expected to further increase in the future, making wake vortex encounters more likely. For this reason fast-time wake vortex models have been developed in the past that predict the vortex position and strength dependent on the aircraft parameters and the ambient conditions in order to avoid dangerous situations. Furthermore, they may reduce flight delays at congested airports as they allow adapting overly conservative separations tactically under certain conditions. However, forecasts include uncertainties that originate from inaccurate and highly variable initial and ambient conditions as well as from inadequate understanding and simplification of the underlying physics. As a consequence, deterministic forecasts are to be complemented by probabilistic envelopes.In the field of meteorology such envelopes are frequently computed by combining the forecasts of multiple independent models to quantify the model uncertainty. This approach, also known as Multi-Model Ensemble (MME), has not only shown to increase the reliability of the probabilistic forecast but also to enhance its deterministic skill. For this reason the capability of the MME approach to improve both deterministic and probabilistic wake vortex forecasts is assessed and existing approaches are further developed in this thesis. Three of the ensemble members have been provided in the frame of a NASA-DLR cooperation. The employed models comprise APA 3.2, APA 3.4 and TDP 2.1 (NASA) and are combined with the DLR model D2P. Several MME approaches are examined, comprising the Direct Ensemble Average...