Journal of Thermal Science Vol.18, No.1 (2009) 74−84 Received: August 2008 Xavier OTTAVY: Dr. Permanent Researcher www.springerlink.com DOI: 10.1007/s11630-009-0074-9 Article ID: 1003-2169(2009)01-0074-11 Doppler Global Velocimeter - Development and Validation with Measurements in a Round Free Jet X. Ottavy, S. Goguey, J. Berthiau and I. Trébinjac Laboratoire de Mécanique des Fluides et d’Acoustique (LMFA), Ecole Centrale de Lyon, 36 av. Guy de Collongue, 69134 Ecully cedex, France Doppler global velocimetry (DGV) has already been shown to be an interesting technique capable of measuring the three components of velocity in a plane. A 1-component DGV system is currently under development at the LMFA, using a stabilized continuous wave (CW) argon ion laser for emission. The receiver features only one camera for both signal and reference images and incorporates a DEFI system to adjust the incident laser light frequency and its transmission coefficient on the iodine cell absorption line. A description of the whole system is presented and a validation with measurements of axial velocities at several positions in a round free jet is pro- posed. Keywords: laser anemometry, Doppler shift, iodine vapor, absorption line filter, DEFI system, image processing. Introduction Doppler global velocimetry (DGV), also called planar Doppler velocimetry (PDV) [1][2][3], or in some cases referred to filtered Rayleigh scattering velocimetry (FRS velocimetry) [4][5], offers the advantage over one-point laser techniques of instantaneously giving hundreds of thousands of measurement points in a plane. The first works began in the 90’s, almost simultaneously, by Ko- mine et al. [6][7] and Miles et al [8]. Since then, a few research groups have been refining this work. The de- velopments of a MHz-rate DGV system [9], of a two-frequency DGV system [10][11], and of a combined technique named PPIDV [12] (planar particle imaging Doppler velocimetry) are worth mentioning. However, no commercial DGV system is available yet. The turbo- machinery Team of LMFA at École Centrale de Lyon is currently developing its own system with a view to ap- plying it for measurements in turbomachines. The aim of the present paper is first to discuss the dif- ferent options and comment on our choices in the devel- opment of our DGV system, and secondly, to validate this system with measurements in a round free jet. Principle of the DGV The DGV is based on the Doppler effect principle, and uses a laser light sheet to illuminate particles seeded in the gas flow. As those particles pass through the illumi- nated plane, they scatter light in all directions, and the frequency of scattered light is shifted from the frequency of the incident light. The resulting Doppler shift Δν is directly linked to the velocity vector V r of the moving particles through the Doppler equation: ( ) 0 0 0 1 . p V V R E ν ν ν λ λ Δ = − = − = r r r (1) where ν is the frequency of the scattered light, ν 0 the frequency of the incident light, λ 0 the incident light wavelength, R r the observation direction and E r the