Pressure Differential Angle of Attack Measuring System

A Step Forward In Stealth Technology– Pressure Differential Angle of Attack Measuring System

U. N. Mughal*1

Assistant Professor,

Mechanical Engineering Department, NED University of Engineering & Technology, Karachi, Pakistan

Email : mughal@neduet.edu.pk, umair.mughal@gmail.com

J. Masud*2

Associate Professor,

Institute of Avionics and Aeronautics Engineering, Air University, Islamabad, Pakistan

Email : jehanzeb.masud@mail.au.edu.pk, polymech@gmail.com

Outline

Flush Port Air Data System (FADS), Theme/Scope of this Research Exercise, Analysis Approach, Analysis of Potential Flow Over Rotating and Non Rotating

Cylinders, Analysis of Flow Over Sphere, Analysis of Flow Over Wedges of Different Half Wedge Angles, Analysis of Flow Over Cones of Different Half Cone Angles, Analysis of Potential Flow Over Low Speed and High Speed Airfoils Comparison of Pressure Differential w.r.t Angle of Attack Between

High Speed Airfoil and Wedge of Comparative Half Wedge Angle Comparison of Pressure Differential w.r.t Angle of Attack Between

Low Speed Airfoil and Cylinder Conclusions

Flush Air Data System

Need of Flush Airdata System:• Pitot Tube.

• Critical Parameters (Dynamic Pressure, Angle of Attack).

• Development of Flush Airdata System (FADS) Function of FADS

• Matrix of Flush Ports

• Pressure Differential

• Online computation

• Potential flow. Advantages:

• Over determined system

• Robustness.

• Error Minimization

• Accuracy

Contd. Flush Air Data System

Port Location depends upon • Large angle of attack sensitivity

• Good linearity with angle of attack,

• Minimum variation of the parameter with Mach number

Used• Hypersonic (X-15)

• Stealth, (B-2, A-12)

• Research aircrafts

• Hybrid System on F-22

Complications• High-fidelity vehicle simulations,

• Pressure ports locations

Theme/Scope of this Research Exercise,

To theoretically analyze the effects of Angle of Attack on Pressure Difference on general aerodynamic bodies like

• Rankine Half Body

• Cylinder

• Sphere

• Wedge

• Cone

• Airfoil

To suggest the best port location on the profiles of the above bodies, in order to install Pressure Differential Angle of Attack measuring instrument on them.

Analysis Approach

Potential Flow Theory for Rankine Half Body, Cylinder & Sphere

Falkan Skan Wedge Flow and Oblique & Expansion wave theory for Wedge

Similarity Solution for 3D Axisymmetric Flow and Conical Shock Wave Theory for Cone

Conformal Mapping for Airfoil Initial Conditions at Sea Level Karman-Tsien Rule for Compressibility Corrections Flow Assumption are

• Steady Flow

• Incompressible Flow

• Irrotational Flow

1. Rankine Half Body

P on Rankine Half Body

Source Strength = 2513ft2/s, Uniform stream at an angle of U=100ft/s

Different values of Stream Function.

Radial and Tangential components of velocities.

Co-efficient of Pressure CP = 1 – (V/U)2

Compressibility Correction of CP

P at corresponding ports.

Difference in Non Compressibility Corrected and Compressibility Corrected Parameters

Streamlines Flow Pattern on Rankine Half Body At Different AOA

Cp Upstream and Cp Downstream

P at Free-stream Velocity

2. Non Lifting Cylinder

P on Non Lifting Cylinder

Doublet Strength = 2513ft2/s, Uniform stream at an angle of U=100ft/s

Radial and tangential components of velocities.

Streamlines Flow Pattern on Non LiftingCylinder At Different AOA

3. Lifting Cylinder

Steps involved to Calculate P on Lifting Cylinder

Doublet Strength = 2513ft2/s, Vortex Strength = vortex of strength 1000ft2/s, Uniform stream at an angle of U=100ft/s

Streamlines Flow Pattern on Lifting Cylinder At Different AOA

4. Sphere

Steps involved to Calculate P on Sphere

3D Doublet Strength = 2513ft3/s, Vortex Strength = vortex of strength 1000ft2/s, Uniform stream at an angle of U=100ft/s

5. Wedge

Steps involved to Calculate P on Wedge

Falkan Skan Wedge Flow Theory, Subsonic Airflow,

Cp calculated using relation,

Cp = 1 – x2/(2-)

P at corresponding ports. Difference in Non Compressibility

Corrected and Compressibility Corrected Parameters

Oblique Shocks and Expansion Wave Theory, Supersonic Airflow on Wedge

Comparision Between Wedge in Subsonic and Supersonic Flow Regimes

6. Cone

Steps involved to Calculate P on Cone

Similarity Solution for 3D Axisymmetric Flow for Subsonic Airflow

Cp calculated using relation, Cp = 1 – x6/(2-)

P at corresponding ports. Difference in Non Compressibility

Corrected and Compressibility Corrected Parameters

Numerical procedure for Supersonic Airflow.

Comparision Between Cone in Subsonic and Supersonic Flow Regimes

7. Airfoil

Generated from Cylinder Using Conformal Transformation

P at Free-stream Velocity on 20% Thick Cambered Airfoil

P at Free-stream Velocity on 6% Thick Cambered Airfoil

Conclusions

Rankine Half Body Best Port Location 600-800

Non Lifting Cylinder Best Port Location 450-600

Lifting Cylinder Best Port Location 600

Sphere Best Port Location 450-600

Wedge Best Port Location SS≈SS Flow

Cone Best Port Location SS≈SS Flow

Airfoil Best Port Location 0.3 to 0.5 x/c

P Varies Linearly With Angle of Attack and Mach Number on all general Aerodynamic Bodies Analyzed

Room for Further Research

Wind Tunnel Testing of all Aerodynamic Bodies which I have used in this Exercise will support in verifying the results.

I have used Conformal Mapping to analyze flow on Airfoil, but Surface Panel Method can also be used in show results in the same direction.

QUESTIONS???

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