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Boundary Layer Oscillation for Aircraft
Cavity/Surfaces : Calibration of Wind
Tunnels (Subsonic/Supersonic)
Chun C Gan
30th March, 2023
MSc Operations Management
[Manchester School Management]
University of Manchester Institute of Science and Technology (UMIST),
United Kingdom.
BEng (Hons) Mechanical Engineering
[Simon Building]
University of Manchester, United Kingdom
Boundary Layer Separation
• The current defined landing gear section design has shown that noise source
from the downstream edge of the cavity contributes to buffeting problem during
take-off and landing, i.e. turbulence due to oscillation of the shear layer from
upstream boundary layer separation to the downstream edge.
• The thickness of this shear layer is approximately 1.5 to 2 mm, base on wind
tunnel experiment in University of Manchester (year 1996), for the flowrate as
stated in the graph below.
Characteristic of Shear Layer Thickness
• It is to show here that the length of the cavity is vary to detect the sinusoidal
wave pattern of the shear layer after it separates from the surface boundary.
• Peak amplitude represents amplification of noise in the flow across cavity.
• In the landing gear section, it is advisable to detect these frequency and
amplitude for higher flow speed, pretty weak detection at low flowrate.
Oscillation of
Shear Layer :
Non-Dimensional
Representation
Subsonic Wind Tunnel
Upstream Boundary Layer Separation
Thickness (
𝑦
δ
) : 1.5 to 2 mm
(Wind Tunnel Experiment in the University of
Manchester)
Oscillation of
Shear Layer :
Influence of Free-Stream
Velocity (Real Figure)
Subsonic Wind Tunnel
For different cavity sizes
𝐿
𝐷
(as shown)
Upstream Boundary Layer Separation
Thickness δ : as shown in graph [mm]
(Wind Tunnel Experiment in the University of
Manchester)
Wind Tunnel Calibration
(pressure)
(P1 – P2) = ρ g h = Δ P ref
(graph plotted as shown, next slide)
P1
P2
h
Air Intake -
Bell mouth/Frictionless
with honeycomb (to
straighten flow) Rectangular Cavity –
Hot probe location
(movable, vertically)
Cylindrical Pitot
Tube
P
Wind Tunnel Calibration – Laboratory Course
Calibration of Wind tunnel (pressure)
1
2
𝜌 𝑉
𝑤𝑠𝑝
2
ΔPref
𝑉
𝑤𝑠𝑝
ΔPref
(P1 – P2) = ρ g h = Δ P ref
Dynamic Pressure, Pdyn = (P – Pwsp) =
1
2
𝜌 𝑉
𝑤𝑠𝑝
2
; where P = total pressure,
Pwsp = wall static pressure
Wind Tunnel Calibration (hot-wire probe)
(for info)
• Eo Ξ due to the natural convection when (v = 0)
• Β and η are empirical constants
• Collis-Williams Law
• 𝐸2 − 𝐸𝑜
2 = 𝐵 ∗ 𝑈𝜂
• log( 𝐸2
− 𝐸𝑜
2
) = 𝑙𝑜𝑔 𝐵 + 𝜂 log U
(graph plotted as shown, next slide)
Wind Tunnel Calibration – Laboratory Course
Calibration of Wind tunnel (hot-wire probe) (for info)
log( 𝐸2
− 𝐸𝑜
2
)
log U
Note : 0.35 <= η <= 0.45
Slope
𝐸𝑜
ΔPref [ proportional to
1
2
𝜌 𝑉
𝑤𝑠𝑝
2
]
E
𝐸2
= 𝐸𝑜
2
+ 𝐵 ∗ 𝑈𝜂
Subsonic Wind Tunnel
Low Flow
MACH < 1
Airflow Across Cavity:
Subsonic Flow
Low Speed
Up to 40 m/s
(3.6 KM/HR = 1 m/s; 40 – 150 KM/HR)
Signal Level
Up to 100 mV
- Frequency
148, 80, 50, 129 Hz
- L/D
1, 1.2, 2, 3
- Feature
Fixed
MACH <= 1
L/D = 1
>Rectangular Cavity
Specifications:
Frequency f 148 Hz
Length L 50 mm
Depth D 50 mm
Width W 460 mm
Airflow Across Cavity:
Subsonic Flow
Low Speed
Up to 40 m/s
(3.6 KM/HR = 1 m/s; 40 – 150 KM/HR)
Signal Level
Up to 100 mV
- Frequency
148, 80, 50, 129 Hz
- L/D
1, 1.2, 2, 3
- Feature
Fixed
MACH <= 1
L/D = 1.2
>Rectangular Cavity
Specifications:
Frequency f 129 Hz
Length L 60 mm
Depth D 50 mm
Width W 460 mm
Airflow Across Cavity:
Subsonic Flow
Low Speed
Up to 40 m/s
(3.6 KM/HR = 1 m/s; 40 – 150 KM/HR)
Signal Level
Up to 100 mV
- Frequency
148, 80, 50, 129 Hz
- L/D
1, 1.2, 2, 3
- Feature
Fixed
MACH <= 1
L/D = 2
>Rectangular Cavity
Specifications:
Frequency f 80 Hz
Length L 100 mm
Depth D 50 mm
Width W 460 mm
Airflow Across Cavity:
Subsonic Flow
Low Speed
Up to 40 m/s
(3.6 KM/HR = 1 m/s; 40 – 150 KM/HR)
Signal Level
Up to 100 mV
- Frequency
148, 80, 50, 129 Hz
- L/D
1, 1.2, 2, 3
- Feature
Fixed
MACH <= 1
L/D = 3
>Rectangular Cavity
Specifications:
Frequency f 50 Hz
Length L 150 mm
Depth D 50 mm
Width W 460 mm
Supersonic Wind Tunnel
High Flow
MACH = 2.3
Airflow Across Cavity:
Supersonic Flow
High Speed
MACH 2.3
(MACH 1 = 343 m/s; 1234.8KM/HR)
Signal Level
Up to 68 mV
Frequency
220, 440, 660, 880, 1100 Hz
L/D
Variable
Feature
Adjustable
Details:
MACH 2.3
L/D = variable
> Circular CavitySpecifications:
Frequency f <see diagram>
Length L (diameter) 50 mm
Depth D <see diagram>
Boundary Layer Oscillation for Aircraft Cavity/Surfaces

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Boundary Layer Oscillation for Aircraft Cavity/Surfaces

  • 1. Boundary Layer Oscillation for Aircraft Cavity/Surfaces : Calibration of Wind Tunnels (Subsonic/Supersonic) Chun C Gan 30th March, 2023 MSc Operations Management [Manchester School Management] University of Manchester Institute of Science and Technology (UMIST), United Kingdom. BEng (Hons) Mechanical Engineering [Simon Building] University of Manchester, United Kingdom
  • 2. Boundary Layer Separation • The current defined landing gear section design has shown that noise source from the downstream edge of the cavity contributes to buffeting problem during take-off and landing, i.e. turbulence due to oscillation of the shear layer from upstream boundary layer separation to the downstream edge. • The thickness of this shear layer is approximately 1.5 to 2 mm, base on wind tunnel experiment in University of Manchester (year 1996), for the flowrate as stated in the graph below.
  • 3. Characteristic of Shear Layer Thickness • It is to show here that the length of the cavity is vary to detect the sinusoidal wave pattern of the shear layer after it separates from the surface boundary. • Peak amplitude represents amplification of noise in the flow across cavity. • In the landing gear section, it is advisable to detect these frequency and amplitude for higher flow speed, pretty weak detection at low flowrate.
  • 4. Oscillation of Shear Layer : Non-Dimensional Representation Subsonic Wind Tunnel Upstream Boundary Layer Separation Thickness ( 𝑦 δ ) : 1.5 to 2 mm (Wind Tunnel Experiment in the University of Manchester)
  • 5. Oscillation of Shear Layer : Influence of Free-Stream Velocity (Real Figure) Subsonic Wind Tunnel For different cavity sizes 𝐿 𝐷 (as shown) Upstream Boundary Layer Separation Thickness δ : as shown in graph [mm] (Wind Tunnel Experiment in the University of Manchester)
  • 6. Wind Tunnel Calibration (pressure) (P1 – P2) = ρ g h = Δ P ref (graph plotted as shown, next slide) P1 P2 h Air Intake - Bell mouth/Frictionless with honeycomb (to straighten flow) Rectangular Cavity – Hot probe location (movable, vertically) Cylindrical Pitot Tube P
  • 7. Wind Tunnel Calibration – Laboratory Course Calibration of Wind tunnel (pressure) 1 2 𝜌 𝑉 𝑤𝑠𝑝 2 ΔPref 𝑉 𝑤𝑠𝑝 ΔPref (P1 – P2) = ρ g h = Δ P ref Dynamic Pressure, Pdyn = (P – Pwsp) = 1 2 𝜌 𝑉 𝑤𝑠𝑝 2 ; where P = total pressure, Pwsp = wall static pressure
  • 8.
  • 9.
  • 10. Wind Tunnel Calibration (hot-wire probe) (for info) • Eo Ξ due to the natural convection when (v = 0) • Β and η are empirical constants • Collis-Williams Law • 𝐸2 − 𝐸𝑜 2 = 𝐵 ∗ 𝑈𝜂 • log( 𝐸2 − 𝐸𝑜 2 ) = 𝑙𝑜𝑔 𝐵 + 𝜂 log U (graph plotted as shown, next slide)
  • 11. Wind Tunnel Calibration – Laboratory Course Calibration of Wind tunnel (hot-wire probe) (for info) log( 𝐸2 − 𝐸𝑜 2 ) log U Note : 0.35 <= η <= 0.45 Slope 𝐸𝑜 ΔPref [ proportional to 1 2 𝜌 𝑉 𝑤𝑠𝑝 2 ] E 𝐸2 = 𝐸𝑜 2 + 𝐵 ∗ 𝑈𝜂
  • 12. Subsonic Wind Tunnel Low Flow MACH < 1
  • 13.
  • 14. Airflow Across Cavity: Subsonic Flow Low Speed Up to 40 m/s (3.6 KM/HR = 1 m/s; 40 – 150 KM/HR) Signal Level Up to 100 mV - Frequency 148, 80, 50, 129 Hz - L/D 1, 1.2, 2, 3 - Feature Fixed MACH <= 1 L/D = 1 >Rectangular Cavity Specifications: Frequency f 148 Hz Length L 50 mm Depth D 50 mm Width W 460 mm
  • 15. Airflow Across Cavity: Subsonic Flow Low Speed Up to 40 m/s (3.6 KM/HR = 1 m/s; 40 – 150 KM/HR) Signal Level Up to 100 mV - Frequency 148, 80, 50, 129 Hz - L/D 1, 1.2, 2, 3 - Feature Fixed MACH <= 1 L/D = 1.2 >Rectangular Cavity Specifications: Frequency f 129 Hz Length L 60 mm Depth D 50 mm Width W 460 mm
  • 16. Airflow Across Cavity: Subsonic Flow Low Speed Up to 40 m/s (3.6 KM/HR = 1 m/s; 40 – 150 KM/HR) Signal Level Up to 100 mV - Frequency 148, 80, 50, 129 Hz - L/D 1, 1.2, 2, 3 - Feature Fixed MACH <= 1 L/D = 2 >Rectangular Cavity Specifications: Frequency f 80 Hz Length L 100 mm Depth D 50 mm Width W 460 mm
  • 17. Airflow Across Cavity: Subsonic Flow Low Speed Up to 40 m/s (3.6 KM/HR = 1 m/s; 40 – 150 KM/HR) Signal Level Up to 100 mV - Frequency 148, 80, 50, 129 Hz - L/D 1, 1.2, 2, 3 - Feature Fixed MACH <= 1 L/D = 3 >Rectangular Cavity Specifications: Frequency f 50 Hz Length L 150 mm Depth D 50 mm Width W 460 mm
  • 18. Supersonic Wind Tunnel High Flow MACH = 2.3
  • 19.
  • 20.
  • 21.
  • 22. Airflow Across Cavity: Supersonic Flow High Speed MACH 2.3 (MACH 1 = 343 m/s; 1234.8KM/HR) Signal Level Up to 68 mV Frequency 220, 440, 660, 880, 1100 Hz L/D Variable Feature Adjustable Details: MACH 2.3 L/D = variable > Circular CavitySpecifications: Frequency f <see diagram> Length L (diameter) 50 mm Depth D <see diagram>