Wake vortex decay in ground proximity physical mechanisms and artificial enhancement

Transkript

1 Wake vortex decay in ground proximity physical mechanisms and artificial enhancement F. Holzäpfel, A. Stephan, T. Misaka Institut für Physik der Atmosphäre, DLR, Oberpfaffenhofen Reinhard Geisler, Robert Konrath Institut für Aerodynamik und Strömungstechnik, DLR, Göttingen what is happening IGE and how can we make use of it bottleneck ground proximity decay mechanism enhancement of vortex decay towing tank experiment large eddy simulation Vortragstitel 1

2 WakeScene-Departure encounter statistics WakeScene-Arrival NATS: reported encounters 2000 to 2004

3 ground effect with crosswind

4 wall-resolved LES of WV evolution IGE with crosswind t* = 1.4 t* = 1.8 crosswind deficit excess z 1 + = z 1 u τ /ν λ z 0 = b 0 = 47.1 m Γ 0 = 530 m²/s t 0 = 26.3 s r c = 3 m V cross = 0.85 w 0 = 1.5 m/s Re = Γ 0 /ν = z min = 0.15 m

5 Ω-loops triggered by boundary layer streaks (downwind vortex below) t* = 0 t* = 1.5 upwind Ω-loops ~ CW deficit at ground t* = 1.5 downwind Ω-loops ~ CW excess at ground t* = 1.8

6 decay mechanism in ground proximity with crosswind 1. formation of secondary vortices favored at CW velocity excess (deficit) for lee (luv) vortex (streaks) 2. stretching and tilting of sec. vortices by prim. vortex causes intense Ω loops (hairpin vortices) t* = Ω shape causes self-induced fast approach to primary vortex 4. after sec. vortex has looped around the prim. vortex, Ω head widens driven by self induction 5. interaction of approaching sec. vortices and prim. vortex cause turbulence and annihilation of vorticity

7 towing tank visualization & stereo PIV rectangular wing span = 175 mm towing tank visualization

8 ground topologies towing tank U b 0 /2 h flat ground U a square profile U a a = 0.19 b 0 a l sinusoidal ground surface a = 0.25 b 0, l = 8.5 b 0

9 visualization flat ground two square profiles towing speed: 2,44 m/s video duration: 5 s (τ = 1.4, 80 b 0 ) X = -550 mm profil 1 X = 0 mm PIV X = 550 mm profil 2

10 Particle Image Velocimetry (PIV) flat ground at square profile at profile: rapid decay no rebound

11 circulation decay (PIV) 0.05 flat Glatter ground Boden profile Profil bei at x = 550 mm profile Profil bei at x = 160 mm profile Profil bei at x = 0 mm Zirkulation [m²/s] time Zeit [s] [s] 2 t 0

12 WV evolution IGE with CW (z 0 = b 0 ) no obstacle square profile (0.19 b 0 )² 20 s s s s 1.67

13 decay mechanism in ground proximity with obstacle 1. early detachment of strong Ω-shaped secondary vortices 2. Ω shape causes self-induced fast approach to PV 3. after SV has looped around PV it separates and travels along the primary vortex (again driven by self induction) 4. the dedicated SV connects to the regular ground effect vortex and thus obtains continued supply of energy 20s s s highly intense interaction of PV and SVs leads to rapid WV decay independent from natural external disturbances 44 s 1.67

14 key mechanisms (with and w/o obstacles) 2. Ω shape causes self-induced fast approach to primary vortex (PV) 3. after SV has looped around PV it separates and travels along the PV (again driven by self induction)

15 WV evolution IGE with CW (z 0 = b 0 ) no obstacle

16 WV evolution IGE with CW (z 0 = b 0 ) square profile (0.19 b 0 )²

17 circulation evolution 52 s x* 0.05 Glatter flat ground Boden Profil profile bei at x = mm Profil profile bei at x = 160 mm Profil profile bei at x = 0 mm Zirkulation [m²/s] Zeit [s] time [s] 2 t 0

18 optimization of obstacles with LES with crosswind square profile (x* = z* = 0.19, x* = 4) 3 square profiles (x* = z* = 0.19, x* = 1, x* = 2) sinusoidal surface (z* = 1, λ* =1) ramp (landing) (z* = 1, l* = 4, γ = 3 ) w/o crosswind square profile (x* = 0.19, z* = 0.1, x* = 8) square profile (x* = 0.19, z* = 0.1, Re = ) square profile (x* = 0.19, z* = 0.1, z 0 * = 0.5 ~ towing tank) plates (x* = 0.19, z* = 0.1, y* = 0.016, y* = 0.22) plates (x* = 0.19, z* = 0.1, y* = 0.016, y* = 0.45) plates (x* = 0.19, z* = 0.05, y* = 0.016, y* = 0.22)

19 selection from obstacle set-ups (t* = 1.06, 28 s) 3 square profiles, wind sinusoidal surface, wind small profile no wind small plates no wind

20 Conclusions & Outlook decay mechanism in ground proximity: Ω-loops triggered by velocity deficits (excesses) at the wall (streaks) actively approaching primary vortices fast interaction & decay exploitation of vortex dynamics to enhance WV decay: suitable obstacles accelerate and enhance natural decay mechanisms IGE independent from weather situation good agreement of towing tank experiments and LES optimal obstacle design and assembly still to be investigated field experiments needed installation of suitable obstacles at runway tails: improve safety by reducing number of wake vortex encounters increase efficiency of wake vortex advisory systems (bottleneck) patent pending