Chapter 7 Laser Doppler Anemometry
Introduction to principles and applications
Contents
• Characteristics and applications of LDA
• Principles of operation
• LDA fibre optical system
• Seeding requirements
• Signal characteristics
• Signal processing
• Data processing
Characteristics of LDA
Invented in 1964
• Velocity measurements in Fluid Dynamics (gas, liquid)
• Up to 3 velocity components
• Non-intrusive measurements (optical technique)
• Absolute measurement technique (no calibration required)
• Very high accuracy
• Very high spatial resolution due to small measurement volume
• Tracer particles are required
Applications of LDA
• Laminar and turbulent flows
• Investigations on aerodynamics
• Supersonic flows
• Turbines, etc.
• Liquid flows
• Surface velocity and vibration measurement
• Hot environments (flames, plasma etc.)
• Velocity of particles
• ...etc.
LDA - Optical principle
• When a particle passes through the intersection volume formed by the two coherent laser
beams, the scattered light, received by a detector, has components from both beams.
• The components interfere on the surface of the detector.