Journal of Engineering Physics and Thermophysics, Vol. 89, No. 2, March, 2016 HYDROGASDYNAMICS IN TECHNOLOGICAL PROCESSES EXPERIMENTAL INVESTIGATION OF THREE-DIMENSIONAL TURBULENT JETS ISSUING FROM A NOZZLE WITH A RECTANGULAR OUTPUT SECTION S. I. Isataev, G. Toleuov, M. S. Isataev, UDC 532.517.4 and Sh. A. Bolysbekova A detailed analysis of average dynamic characteristics of flow in a nozzle with a rectangular output section in relation to the nozzle aspect ratio parameter and Reynolds number has been carried out and its results have been generalized. It has been established that the flow velocity profile on the jet axis in the nozzle is determined by the parameter of its aspect ratio and by the jet initial velocity. A semiempirical formula that describes well the change in the maximum flow velocity in the main section of a three-dimensional jet is suggested. Keywords: rectangular nozzle, aspect ratio parameter, axisymmetric jet, three-dimensional turbulent jet, coherent structure. In works [1–7] devoted to an experimental investigation of three-dimensional turbulent jets issuing from nozzles with a rectangular output section, a number of interesting features have been revealed, such as the deformation of the cross section of a jet, its anisotropy, and the presence, in such jets, of three regions of their axial velocity attenuation (the initial section with U ax = const, transition section with U ax ~ x –0.5 , and the main section with U ax ~ x –1 ). These distinctive features of the development of three-dimensional jets manifest themselves differently with change in the nozzle aspect ratio λ = a/b, where a and b are the dimensions of the long and short sides of the nozzle, respectively. The indicated features of a three- dimensional turbulent jet in a nozzle with a rectangular output section are mainly explained by the development of coherent flow structures in it [2, 8, 9], which is an important subject of research. It is also important to continue investigations of the averaged characteristics of flow in a nozzle of this kind. The purpose of the present work is to analyze experimental data on the change of the averaged characteristics of flow in a nozzle with a rectangular output section depending on the Reynolds number and the nozzle aspect ratio parameter λ, with the remaining flow parameters kept intact. Experimental investigations were carried out on a setup consisting of a fan, a vibration-quenching transition section, a plenum chamber, and a nozzle with the output section of rectangular shape. Changeable nozzles were used to form three- dimensional jets. In the experiments we used nozzles whose aspect ratios were λ = 1, 2.66, 5.07, 7.61, 11, 16, and 25.25, as well as a circular nozzle. The nozzles profiled according to Witoszynski′s formula have the same length of 90·10 –3 m and contraction close to 10, with the areas of all the nozzle outputs being approximately the same and equal to the area of the circular nozzle of diameter d cir = 22.57·10 –3 m. In this connection, the effective diameter of each rectangular nozzle d ef was approximately the same as the diameter of the circular nozzle. The pressure and velocity distributions at the outputs of all the nozzles were uniform. Main measurements were made at the flow rates at the nozzle output U 0 = 20 and 40 m /s, which corresponded to the Reynolds numbers 3.2·10 4 and 6.5·10 4 based on the effective nozzle diameter Re = ν ef 0 d U . To measure the mean flow velocity in a nozzle, we used a Pitot tube and an MMN-240 microanemometer. The error involved in measuring this velocity was mainly connected with the accuracy of microanemometer readings. The microanemometer makes it possible to measure even low velocities with an accuracy of up to 3%. The intensity of the flow turbulence at the nozzle output, estimated from the fluctuations of its longitudinal velocity, amounted to 0.025–0.27%. 0062-0125/16/8902-0391 ©2016 Springer Science+Business Media New York 391 Al-Farabi Kazakh National University, 71 al-Farabi Ave., Almaty, 050040, Kazakhstan; email: misatayev@mail.ru. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 89, No. 2, pp. 383–387, March–April, 2016. Original article submitted February 11, 2015. DOI 10.1007/s10891-016-1388-6