594. OPTIMIZATION OF ULTRASOUND BEAM TRANSMISSION PATH WITHIN MEASUREMENT CHANNEL OF ULTRASONIC FLOWMETER. A. RAGAUSKAS 1 , V. PETKUS 2 , P. BORODIČAS 3 , R. BANSEVIČIUS 4 , R. RAIŠUTIS 5 , R. BARAUSKAS 5 , V. PAMAKŠTIS 6  VIBROENGINEERING. JOURNAL OF VIBROENGINEERING. DECEMBER 2010. VOLUME 12, ISSUE 4. ISSN 1392-8716 582 594. Optimization of ultrasound beam transmission path within measurement channel of ultrasonic flowmeter A. Ragauskas 1 , V. Petkus 1 , P. Borodičas 2 , R. Bansevičius 2 , R. Raišutis 3 , R. Barauskas 4 , V. Pamakštis 5 . 1 Telematics Sci. Lab., Kaunas University of Technology, Studentu 50, Kaunas, Lithuania e-mail: telematics@ktu.lt 2 Mechatronics Centre for Research, Studies and Information, Kaunas University of Technology, Kestucio 27, Kaunas, Lithuania e-mail: ramutis.bansevicius@ktu.lt, paulius.borodicas@axis.lt, 3 Ultrasound Institute, Kaunas University of Technology, Studentu 50, Kaunas, Lithuania e-mail: renaldas.raisutis@ktu.lt 4 Dept. of System Analysis, Kaunas University of Technology, Studentu 50-407, Kaunas, Lithuania e-mail: rimantas.barauskas@ktu.lt 5 Dept. of Innovations, AB Axis Industries, Kulautuvos 45A, Kaunas, Lithuania e-mail: virgilijus.pamakstis@axis.lt (Received 30 September 2010; accepted 9 December 2010) Abstract. The numerical simulation of the water flow through the semicircular duct is presented. The results of the simulation show that by implementing such duct into ultrasonic time-of-flight flowmeters it is possible to get an almost flat and linear function of hydrodynamic correction. The optimal choice of the dimension of ultrasonic transducers and the optimal positioning of them allows us to achieve a hydrodynamic function with the slope ~ 4%. It is expected that flat hydrodynamic calibration function gives the possibility to expand the dynamic measurement range of ultrasonic flowmeters and to increase stability and repeatability of the measurement results. Keywords: ultrasonic flowmeter, ultrasound wave propagation in duct, hydrodynamic correction, flow profile. Introduction A typical ultrasonic flowmeter working on time-of-flight measurement principle suffers from the non-linearity of the hydrodynamic correction function within a wide dynamic measurement range. Moreover, the temperature changes of the flowing liquid affect the changes of kinematic viscosity of the liquid and it requires additional correction of the hydrodynamic functions [1]. These factors limit the accuracy class and dynamic measurement ranges of the contemporary flowmeters. The known methods for solving this problem are: - the implementation of additional functions of temperature measurement and the correction of temperature-dependent hydrodynamic errors of the flow and heat measurement devices [1], - the arrangement of the multi-path scanning of the flow velocity profile by means of the ultrasonic time-of-flight measurement technique [2], - the introduction of special measurement channels with a triangular, rectangular or hexagonal cross-section and the transmission of the ultrasonic pulse into the spiral acoustic path along the measurement channel [3-8].