7/48 7.1.1 Flow Visualization -Schlieren ◆Schlieren Similar physics bases as shadowgraphy; The collimated light is focused with a lens,and a knife-edge is placed at the focal point,positioned to block about half the light. It Measures the first derivative of density in the direction of the knife-edge; Schlieren imaging of a focusing ultrasonic transducer http://en.wikipedia.org/wiki/Schlieren_photograph 8/48 7.1.1 Flow Visualization -PIV Principle Laser light sheet △y Flow plane At time between two pulses Velocity at A Ax particle displacement in x direction Ux=Ax/ras△f+0 Ay particle displacement in y direction Uy=△y/△t as At+0 Fig.7.1(a)Particle Image Velocimetry. Using multiple-exposure method,the location of particles at two times separated by a known time interval are used to compute the magnitude and direction of the particle's velocity.7.1.1 Flow Visualization - Schlieren Color schlieren image of the thermal plume from a burning candle, disturbed by a breeze from the right. Photographed by Gary S. Settles, Penn State University http://en.wikipedia.org/wiki/Schlieren_photograph ‹ Schlieren z Similar physics bases as shadowgraphy; z The collimated light is focused with a lens, and a knife-edge is placed at the focal point, positioned to block about half the light. z It Measures the first derivative of density in the direction of the knife-edge; Shock waves produced by a T-38 Talon during flight Schlieren imaging system setup: linear lens-based configuration Schlieren imaging of a focusing ultrasonic transducer 7/48 7.1.1 Flow Visualization – PIV Principle Fig. 7.1(a) Particle Image Velocimetry. Using multiple-exposure method, the location of particles at two times separated by a known time interval are used to compute the magnitude and direction of the particle’s velocity. 8/48