Fluid Mechanics and Acoustics Laboratory - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France


Supervisory authorities

Our partners




Home > Research Support > Scientific instrumentation > Techniques > Rayleigh scattering

Rayleigh scattering

Rayleigh scattering

Optics method based on the Rayleigh scattering: light diffused by particles smaller than the incidental wavelength. From a physical perspective, the spectral content of the diffused light is related to the temperature and to the velocity; it’s intensity is related to the density ρ.


Physical principles


Implementation


- A photomultiplier is a transducer generating an electrical impulse when a photon is interacting with the photosensitive area of the sensor.
- The level of the signals obtained by Raileigh scattering is very weak and dominated by some noise called shot noise (noise from the photon).
- The pile-up effect is the limitation of the measurement of the photon flux maximum value related to the time constants of some sensors types.


Applications

JPEG - 868.8 kb
Jets compressibles à haut nombre de Reynolds en environnement anéchoique (photo LMFA)

Experimental validation

Results comparison with a direct measurement of the temperature fluctuations by Constant Voltage cold wire Anemometry (CVA).
Cold wire sensors geometry:
- figures a & c: d = 3.1 µm; l = 1.25 mm; tc = 306.0 µs
- figures b & d: d = 1.0 µm; l = 0.40 mm; tc = 40.04 µs

  • Incompressible wake of a heated cylinder
    JPEG - 211.3 kb
    Spectres de température dans le sillage d’un cylindre chauffé x=5D z=0.5D
  • Incompressible mix layer of a hot jet
    JPEG - 212.5 kb
    Spectres de température dans la couche de mélange d’un jet chaud x=8D z=0.6D

- Gray: Rayleigh scattering
- Black: uncorrected CVA of the wire thermal inertia
- Red: "hardware" corrected CVA of the wire thermal inertia
- Green: "sofware" corrected CVA of the wire thermal inertia
- Blue: a posteriori "hardware’ corrected CVA of the wire thermal inertia

The errors are relatives to the Rayleigh scattering measurements


— > Développement d’une méthode de mesure de la masse volumique par diffusion Rayleigh appliquée à l’étude du bruit de jet, et contribution à l’étude du screech dans les jets supersoniques sous détendus (Mercier.B, Thèse de Doctorat, 2017).pdf
— > High frequency temperature fluctuation measurements by Rayleigh scattering and constant‑voltage cold‑wire techniques (Mercier B, Jondeau E, Castelain T, Ozawa Y, Bailly C, Comte‑Bellot G, Experiments in Fluids, 2019).pdf