A Simple Wake Vortex Encounter Severity Metric

Transcription

1 A Simple Wake Vortex Encounter Severity Metric Rolling Moment Coefficient due to Encounter of an Aircraft with a Wake Vortex Vincent TREVE (EUROCONTROL) Ivan DE VISSCHER and Grégoire WINCKELMANS (WaPT as EUROCONTROL contractor)

2 Aircraft separations today For congested runway (during peak hours), separations are primarily imposed by ICAO wake turbulence separations MTOM 7T 7T < MTOM <136T MTOM 136T Light Medium Heavy

3 Rationale behind wake turbulence separation Wake Vortex Encounter (WVE)-related hazard : rolling motion of the follower Simulation by UCL 3

4 Airport congestion today and in the near future Analysing summer period 2012, 6 airports were congested in the sense of operating at 80% or more of their capacity for more than 3 hours per days. This is expected to grow to 30 airports in however through bilateral discussions with airports, it appears that today many more airports have constrained peak hours (<3h) during which runway capacity is either a source of delay OR a limitation to business development.

5 Tomorrow separations will be resulting from very different solutions ICAO RECAT-EU: 6 wake categories RECAT2-EU: pairwise separation Revision of separation standards Time-Based Separation Weather-Dependant Separation Separation function of weather conditions Enhanced Procedures Revision of procedure

6 Separation based on a more efficient schemes: European Wake Re-categorisation ICAO RECAT-EU: 6 wake categories RECAT2-EU: Pairwise separations Watch video =

7 RECAT Principles: relative safety assessment If this is safe 5 NM this is over conservative 5 NM 7

8 RECAT Principles: relative safety assessment If this is safe 5 NM this is over conservative Reduced 8

9 Wake Vortex (WV) description: Roll-up and initial characteristics Aircraft wake rolls up to form a two-vortex system Vortex spacing b 0 = s b l, function of aircraft span b l wing and HTP design and configuration Vortex circulation Γ 0 = function of aircraft mass M aircraft flight speed V vortex spacing b 0 M g ρ V b 0, Photos ONERA: aircraft model in catapult facility

10 Wake vortex circulation distribution Simulation by UCL

11 Wake vortex circulation evolution Γ tot 0 = Γ 0 Vortex circulation decay influenced by atmospheric turbulence thermal stratification ground proximity Γ tot In Ground Effect (IGE) Strong interaction with the ground-generated boundary layer inducing rebound of the vortices enhanced decay t Simulation by UCL

12 Parameters influencing the follower aircraft rolling motion (S f, c y, C l,α,eff (y)) Γ(r)/Γ tot V f Γ tot y v z v b l Γ tot Leading order parameters Vortex circulation Γ tot Follower span Follower flight speed V f Follower wing area S f Second order parameters Vortex circulation distribution Γ(r)/Γ tot Follower wing effective lift slope coefficient C l,α,eff y Vortex position w.r.t. aircraft (y v, z v ) Follower chord distribution c(y)

13 Rolling Moment Coefficient (RMC) RMC = RMC = Vortex induced rolling moment on the follower M v 1 2 ρ V f 2 S f Follower parameters S f M v V f

14 Airbus flight encounter tests for A380 Generator Follower A346 anda380 as wake generator Constant track, speed and altitude AIRBUS A320 or AIRBUS A Various separations AIRBUS A380 or AIRBUS A ~1,000 ft 4 NM (A343) 5 NM (A343, A320) 6 NM (A320) A346 A380 A320, A343 Roll Rate Roll Acceleration Rolling Moment A380 anda346 wakes made visible by oil injection Followerrelative flight path A320, A343 as encounterer usually horizontally through the wakes at lateral encounter angle Z

15 Airbus flight encounter tests for A380

16 Airbus flight encounter tests for A380 Objective: separation design behind A380 Cruise test with contrails Difficult to collect a sufficient amount of data to allow separation design Hence, recommendation by EASA Use the data to validate a severity metric model Use that model for separation design (not only for A380) RECAT Reference: Closure report for A380 Wake Turbulence Separation Safety Case A380 with oil spray system Source: Airbus (2009)

17 Airbus flight encounter tests results: WVE metric Wake strength (circulation) Γ tot vs Rolling Moment M v Problem: Large variation of rolling moment for a same circulation value depending on follower type Generator Follower AIRBUS A320 or AIRBUS A Same separation AIRBUS A380 AIRBUS A320 AIRBUS A

18 Airbus flight encounter tests results: WVE metric Rolling Moment M v Problem: aircraft ability to recover is not taken into account Rolling Moment Coefficient (RMC) Advantage: allow direct comparison between various aircraft pairs RMC from measurements : RMC = M v 1 2 ρ V f 2 S f RMC approximation by dimensional analysis: RMC Γ tot V f Obtained from measurements Obtained from manufacturer s data

19 Measured RMC vs Γ tot V f Large variation of the metric for a same RMC value Increased differences between aircraft pairs that are not observed in the measurements

20 Improved Rolling Moment Coefficient (RMC) computation RMC = Γ tot V f C l,α,eff 2π F c y c, Γ r Γ tot, y v, z v (S f, c y, C l,α,eff (y)) Γ(r)/Γ tot V f Γ tot y v z v b l Γ tot

21 RMC computation: vortex location RMC = Γ tot V f C l,α,eff 2π F c y c, Γ r Γ tot, y v, z v Assumptions G tot z v G tot y v Assumption 1: Centered wake vortex encounter

22 RMC computation: vortex circulation distribution RMC = Γ tot C l,α,eff V f 2π F c y c, Γ r, y v, z v Γ tot b l Assumptions Γ(r) Γ tot = r b l r b l a 2 Assumption 2: Burnham-Hallock vortex circulation distribution with parameter a=0.04

23 RMC computation: follower wing chord distribution RMC = Γ tot V f C l,α,eff 2π F c y c, b l, y v, z v Assumptions Assumption 3: Elliptical chord distribution assumed for all followers

24 RMC computation: Effective lift slope coefficient RMC = Γ tot V f C l,α,eff 2π F c y c, b l, y v, z v Assumptions Prandtl correction C l,α,eff = C l,α AR AR + 2 with C l,α = 2 π Assumption 4: Effective lift slope correction corresponding to that of level flight

25 Improved Rolling Moment Coefficient (RMC) RMC = Γ tot V f AR AR + 2 F b l Assumptions with F b l = 1 2 2a b l 1 + 2a b l 2 2 a b l and a = 0.04 Used for the RECAT-EU relative safety assessment Endorsed by EASA

26 Measured RMC vs RECAT-EU metric Best linear fit: 1.12 R 2 of linear fit: 0.82 Mean deviation: RMS deviation:

27 Measured RMC vs Γ tot V f Best linear fit: 1.71 R 2 of linear fit: 0.77 Mean deviation: RMS deviation:

28 Further improved Rolling Moment Coefficient (RMC) computation RMC = Γ tot V f C l,α,eff 2π F c y c, Γ r Γ tot, y v, z v Refinement and further justifications of the assumptions made Additional evidences required to allow pairwise separation design for RECAT-2 Γ(r)/Γ tot V f (S f, c y, C l,α (y)) Γ tot y v z v b l Γ tot

29 Improved RMC computation: vortex circulation distribution RMC = Γ tot C l,α,eff V f 2π F c y c, Γ r, y v, z v Γ tot b l Assumptions Γ(r) Γ tot = r b l r b l a 2 Assumption 2: Burnham-Hallock vortex circulation distribution with parameter a=0.035

30 B-H vortex parameter from energy-based analysis Determination of the a parameter by equating the kinetic energy of the near-wake cross-flow (determined from circulation distribution) to that of the resulting rolled-up two-vortex system made of B-H vortices Example: Elliptic loading E 0 Γ 0 2 = π 8 s = b 0 b l = π 4 a =

31 B-H vortex parameter from energy-based analysis Clean configuration Circulation distribution s a Elliptic (p=2) π/ Hyper-elliptic (p=2.5) Hyper-elliptic (p=3) Landing configuration : Circulation distribution s a Double hyper-elliptic (p 1 =2.5, p 2 =3) Double hyper-elliptic (p 1 =2.5, p 2 =3.5)

32 Improved RMC computation: Effective lift slope coefficient RMC = Γ tot V f C l,α,eff 2π F c y c, b l, y v, z v Assumptions Global correction for the case of a WVE AR, with C AR+4 l,α = 2 π C l,α,eff = C l,α Assumption 4: Effective lift slope correction obtained from solving Prandtl equation for the case of a WVE

33 Effective lift slope in wake encounter: C l,α,eff Case of an elliptical wing in level flight Uniform effective lift slope along the span (Prandtl correction) AR C l,α,eff = C l,α AR + 2 α e = α α d AR AR + 2 α

34 Effective lift slope in wake encounter: C l,α,eff Case of an elliptical wing encountering a B-H vortex and C l,α = 2π A posteriori and global fit of the obtained induced RMC RMC = Γ tot V f AR (AR + C) C l,α 2π F b l C l,α,eff 2 π C = 4. 0 consistently obtained. Example with AR=10 and a b l = 4%

35 Improved Rolling Moment Coefficient (RMC) RMC = Γ tot V f AR AR + 4 F b l Assumptions with F b l = 1 2 2a b l 1 + 2a b l 2 2 a b l and a = Used for the RECAT2-EU relative safety assessment

36 Measured RMC vs RECAT2-EU metric Best linear fit: 0.98 R 2 of linear fit: 0.82 Mean deviation: RMS deviation:

37 Measured RMC vs RECAT-EU metric Best linear fit: 1.12 R 2 of linear fit: 0.82 Mean deviation: RMS deviation:

38 Measured RMC vs Γ tot V f Best linear fit: 1.71 R 2 of linear fit: 0.77 Mean deviation: RMS deviation:

39 Measured RMC vs RECAT2-EU metric Best linear fit: 0.98 R 2 of linear fit: 0.82 Mean deviation: RMS deviation:

40 Conclusion Justification of the RMC metric by Dimensional analysis Detailed analysis of wake vortex core parameter for wing in landing configuration Prandtl equation solving for effective lift slope coefficient for wing in WVE situation Verified against WVE flight test as recommended by EASA Observed low infuence of WV position wrt follower Oberved low influence of detailed wing shape Use for RECAT-EU, A350, RECAT2-EU

41 Question?