Wake vortex encounter modelling, simulation, assessment, avoidance and alleviation

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 1

Carsten Schwarz Dennis Vechtel, Jana Schwithal, Dietrich Fischenberg, Tobias Bauer, Nicolas Fezans DLR Institute of Flight Systems

Wake vortex workshop 2016 DLR Braunschweig 08 JUNE 2016

Wake vortex encounter research Motivation and background • Wake encounter severity

• physical understanding important • severity assessment –

core element of procedure/ system design/ certification

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 2

• DLR Institute of Flight Systems • 16 years of wake encounter

research • numerous internal and EU-

projects and activities, industry contracts

• inter-disciplinary DLR framework • large research facilities:

aircraft and simulators

• DLR: Wake Vortex I & II Weather and Flying WoLv, L-bows

• EU: WakeNet-Europe

• contracts:

• cooperation/ standardisation: FAA/NIA, Eurocontrol, SAE, RTCA

1999 2001 2003 2005 2007 2009 2011 2013 2015

WakeNet2-Europe

DLR Flight Systems: wake vortex activities and cooperation

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 3

proposal

• Modelling and Simulation

• Severity assessment

• Wake turbulence separations

• Aircraft systems

Wake vortex encounter research Topics

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 4

Steve Morris

_______ measured -------- reconstructed motion induced

Modeling the wake vortex encounter Validated with flight tests Vortex model (flow field)

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 5

t [s]

alph

a [d

eg]

approach

cruise

Wake characterisation sheet

Airbus A320 Date: 30/3/2011 Cruise: FL 360 Wind: 268°/ 31 kt Weight: 62 t Duration: 8 min Heading: 251° Config.: CLEAN TAS: 440 kt

distance [nm]

tota

l circ

ulat

ion Γ

[m2 /s

]

lat.

posi

tion

[m]

Flig

ht L

evel

Circulation

Wake descent

distance [nm]

Lateral spacing

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 6

• Aerodynamic interaction/ aircraft reaction model: strip method

t [s] _______ simulation model output _______ flight test data

Modeling the wake vortex encounter Validated with flight tests

• Model improvement with CFD data

• Verification of local aerodynamic forces with pressure distribution

• Identify improvements for strip method

Wake vortex encounter pressure distribution – DLR project Digital-X/ DLR Institute of Aerodynamics and Flow Technology

Wake encounter severity assessment Simplified Hazard Area (SHA)

• „How close can an aircraft fly safely to a wake vortex?“

• concept: Simplified Hazard Area (SHA)

• conservative/ non-hazard approach, safe and undisturbed operations possible outside the hazard area, no go-arounds

• simple, robust severity criterion • roll control ratio: one parameter to cover complete A/C reaction • validated with pilot-in-the loop simulator & flight tests • dynamic hazard area size (vortex decay, weather) • A/C categories and individual/ pairwise

Roll control ratio RCR

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 7

• Using analytical models of straight vortices in aircraft simulation is simple for modelling but also a simplification compared to reality

• Therefore DLR also uses more sophisticated flow fields generated with LES for aircraft encounter simulation

• Encounter simulations during approach with pilots-in-the-loop in various full-flight-simulators and in-flight simulation with ATTAS

• Offline simulations for parameter variation during approach (OGE) and in ground vicinity (IGE)

• Investigation of the influence of vortex deformation (OGE + IGE), end effects and plate lines (IGE)

Wake encounter severity assessment Simulations with sophisticated vortex flow fields

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 8

Wake encounter severity criteria Selected results

no universal wake encounter severity criteria available!

additional activities: • CREDOS (EU FP 6) • WakeNet3-Europe (EU FP 7) • FAA risk matrix activity • RECAT/ SESAR

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 9

• RCR < 1 acceptable WVE [1972, Robinson, G. H., Larson, R. R.]

• RCR < 0.5 acceptable WVE [1988, Rossow V. J., Tinling, B. E.]

• RCR < 0.2-0.3 appropriate limit for acceptable WVE [1998, Stewart E. C.]

• RCR < 0.5 + 0.006⋅HRCRmax GA prediction [2002, Höhne,G., Reinke, A., Verbeek, M.]

• RCR < 0.2 operationally safe WVE [2006, Hahn, K.-U., Schwarz, C.]

• RCR < 0.2-0.3 operationally safe WVE including vortex deformation [2013, Vechtel, D.]

• Below RCRmax = 0.2 – 0.3 wake vortex impact • is acceptable • cannot be distinguished from other acceptable atmospheric disturbances

such as gusts, light turbulence or thermal • This outcome applies for

• intermediate and final approach • small encounter angles (typical for those flight phases) • roll-dominated and also less roll-dominated encounters

• and includes effects such as • vortex deformation due to the Crow instability • vortex ring formation

• Cruise flight phase to be investigated

Wake encounter severity assessment DLR’s general findings

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 10

Not every encounter with RCRmax > 0.2 is unacceptable, but below this value encounters can be considered non-hazardous

Simplified Hazard Area Prediction (SHAPe)

• all relevant wake vortex parameters parameterized based on MTOW with boundary fits

• determination of hazard area depending on vortex strength and RCR (worst case approach)

• dimension of safety area for any (generic) aircraft pairing

generator MTOW

follower MTOW

SHAPe

generator data

follower data

SHA calculation

A/C data base, e.g. b=f(MTOW)

SHA dimensions

RCR limit circulation

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 11

• Development of separation prediction tool WSVBS („Wirbelschleppenvorhersage und Beobachtungssystem“)

• Development of risk analysis/ assessment tool WakeScene • RECAT: Eurocontrol recategorisation activities

• contributions regarding severity assessment, involvement in Eurocontrol Wake Vortex Task Force

• RECAT-EU introduction started March 2016 in France

Wake turbulence separations

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 12

• Wake impact alleviation control system: reduce wake-induced aircraft reaction

• Safety increase • Reduce risk of injuries • Possibly far term enabler for reduced separation

minima with maintained safety capacity gain

• Information of forward-looking Doppler LiDAR sensor used to generate alleviating control commands

• Questions:

• What are the required LiDAR properties? • What is technologically feasible?

Wake Impact Alleviation

DLR Institute of Flight Systems > C. Schwarz • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 13

Control Actions

Sensor Measurements

Signal Processing

?

• Remote LiDAR (Light Detection and Ranging) sensor measures line-of-sight components of wind velocities in front of aircraft

• Online Wake Identification (OWI) estimates parameters of wake vortex model on basis of LiDAR measurement

• Wake Impact Alleviation Control (WIAC) determines wake-induced disturbance moments resulting from detected wake vortex model and commands control surface deflections which compensate for this disturbance

Concept of Wake Identification Based Wake Impact Alleviation Control

DLR Institute of Flight Systems > C. Schwarz • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 14

partly in cooperation with Airbus

• Success of wake identification and impact alleviation strongly depends on characteristics of lidar sensor

• analysis of sensor requirements ongoing in exchange with lidar experts • Alleviation of wake-induced bank angle of up to 95% and about 70% on average

possible

• Future studies: Anaysis and extention of OWIDIA system for deformed vortices

Wake Impact Alleviation Results and outlook

DLR.de • Chart 15 DLR Institute of Flight Systems > C. Schwarz • Wake vortex encounter research > JUNE 2016

w/o OWIDIAwith OWIDIA5° lateral encounter

A320 behind A340

• functionality as safety net / assistance system (increase of situational awareness)

• basic function: identification of a predicted, imminent or even current wake vortex encounter

• system extension: resolution of conflict by recommendation of tactical small-scale evasion manoeuvres

• conceivable to integrate wake encounter alleviation by F/CTL

Wake Encounter Avoidance & Advisory (WEAA)

DLR’s objectives: system proof-of-concept under operational conditions (in-depth investigation of selected components, comparative studies, benefit analysis)

Objectives: airborne information and warning system prevention of dangerous wake vortex encounters in all phases of flight

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 16

Exploitation of Existing DLR Knowledge for WEAA Components • Meteorological Data Fusion

(Airbus cooperation)

• Vortex Prediction Model: P2P (HOLZÄPFEL, DLR Atmospheric Physics)

• probabilistic two-phase model • effects of a/c configuration, wind,

wind shear, turbulence, stratification and ground proximity

• real-time capability • extensively validated on LIDAR

measurements and LES

• Hazard Assessment: SHAPe (HAHN, SCHWARZ, DLR Flight Systems)

• hazard rating by means of roll control ratio RCR

• simplified hazard areas (rectangular or elliptical)

• Conflict Detection (Airbus cooperation)

0.1 < RCR ≤ 0.2

0.2 < RCR ≤ 0.3

0.3 < RCR ≤ 0.5

0.5 < RCR ≤ 1.0

1.0 < RCR

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 17

WV Warning and Avoidance – HMI Navigation Display – Scientific Mode

own track prediction

conflict position

current vortex wake

generator track prediction generator position

(past) generator track (scientific mode only)

time and distance to conflict

Conflict Warning

proposed avoidance trajectory

distance and bearing to generator (for flight test safety only)

Conflict Resolution

NB these are engineering displays for development of the system functions and not necessarily final designs for the operational pilot HMI

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 18

WEAA Flight Test Campaign 2014 with ATRA and Falcon F-20E

encounter distance ~ 4 nm

Feasibility demonstration of WEAA conflict detection under operational conditions

3 trial flights in April 2014 from Braunschweig 70+ intentional wake encounters for validation of

operational wake vortex prediction and visualisation, conflict detection

experience brought to standardisation activities (RTCA - wake vortex tiger team, SAE G-10WV)

DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016 DLR.de • Chart 19

www.DLR.de • Slide 20

Sample Encounter Video

Synergies with corresponding activities (1/2) Formation flight/ wind turbine wakes Cruise formation flight trim results – fuel benefits

Wind turbine wake roll control ratio – glider aircraft

DLR.de • Chart 21 DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016

Δ Fuel Flow [%]

leader

sweet spot

drawn to scale

wind 10 m/s

drawn to scale

x [m]

z [m]

Synergies with corresponding activities (2/2) Aerial refueling / Load control based on remote gust sensing

DLR.de • Chart 22 DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016

Modelling activites within aerial refueling projects

Lidar-based gust sensing and feedforward load alleviation

DLR Institute of Aerodynamics and Flow Technology

Airbus

position

vertical wind

• Wake turbulence separations/ wake encounter severity assessment

• Aircraft systems

• Wake impact alleviation:

wake measurement and identification based wake impact alleviation control

• Cockpit wake information and warning

Future wake turbulence activities

DLR.de • Chart 23 DLR Institute of Flight Systems > C. Schwarz et al. • Wake vortex encounter research > JUNE 2016

Steve Morris