REPUBLIC OF SERBIA

MINISTRY OF DEFENCE

www.mod.gov.rs

MINISTRY OF DEFENCE

Material Resources Sector

Defensive Technologies Department

Military Technical Institute

www.vti.mod.gov.rs

OVERVIEW OF UNCERTAINTY SOURCES IN flow velocity vector MEASUREMENT by LDA

Slavica Ristić

Institute Goša,  Belgrade, Serbia, s1avce@yahoo.com

Jelena Ilić

Facuty of Mechanical engineering, University of Belgrade, Serbia

Ognjen Ristić

Institute Mihajlo Pupin,  Belgrade, Serbia

Djordje Čantrak,

Facuty of Mechanical Engineering, University of  Belgrade,  Serbia

Slobodan Tašin

Faculty of Technical Sciences, University of Novi Sad,   Serbia

Abstract: Many sources of uncertainties are inherent in LDA practices and must be recognized to obtain good experimental results. Analysis of uncertainty, for tests that include LDA measurements of velocity vectors in wind tunnels or in cylindrical pipe swirl flows is very complex problem. An overview of the most significant uncertainty sources in the LDA measurements is presented. One of the main groups of uncertainty sources is determined by the optical components arrangement. In this paper, special attention is paid to estimation of laser-Doppler anemometry uncertainty of measurement volume positioning in test devices caused by the wind and water tunnel windows thickness, or by the pipe wall curvature (without using refractive index matching). The required corrections, for measurements of velocity components such: shift of measuring volume and its orientation are analyzed and determined for VTI wind and water tunnels and for some very often used geometry of cylindrical pipes in industry. Depending on different experimental conditions, some of these sources of uncertainty may be neglected, but generally, it is necessary to take into account all of them in all optical methods, as LDA, PDA, PIV and so on.

Key words: LDA, measurement uncertainty, wind and water tunnel, cylindrical pipe.