Hydraulic Flow Instability in a Ranque Tube
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HYDRAULIC FLOW INSTABILITY IN A RANQUE TUBE M. Kh. Pravdina, I. K. Kabardin∗ , V. I. Polyakova, D. V. Kulikov,
UDC 532.516
V. G. Meledin, V. A. Pavlov, M. R. Gordienko, and N. I. Yavorsky
Abstract: The flow in a Ranque tube with a square cross-section channel has been studied using the hydraulic concept of strongly swirling flow with a circulation zone. Based on experimental data, it has been found that for flow in a vortex tube, the hydraulic condition of flow crisis is satisfied: the longitudinal velocity becomes equal to the velocity of propagation of centrifugal waves at the boundary between the vortex and the circulation zone. It has been shown that the temperature variation along the flow occurs mainly in the region of the working channel in which the ratio of the longitudinal velocity at the vortex boundary to the propagation velocity of centrifugal waves fluctuates about unity. The existence of a previously unknown energy separation mechanism due to the presence of hydraulic jumps in the development of internal waves in a Ranque tube was assumed. Keywords: vortex tube, centrifugal waves, flow crisis, hydraulic jump. DOI: 10.1134/S0021894420030098
1. Investigation of the temperature separation and fields of hydrodynamic quantities in a transparent Ranque tube with a square cross-section channel started in [1], where large-scale vortex structures were detected in a region adjacent to the hot flow outlet using the Foucault–Hilbert method. A square cross-section of the working channel was selected for the ease of using optical methods for studying the flow in the tube. The working channel of the tube consists of three identical sections with transparent windows in opposite faces. A diagram of the tube and Cartesian coordinate axes are shown in Fig. 1; the dimensions of the working channel are 390×34×34 mm. With the advent of detailed non-contact velocity measurements in flow, studies with this tube were continued [2–5]. It was required to obtain detailed data on the flow structure, velocities, and temperatures at the inlet and outlet as well as inside the tube for the same (if possible) geometric configuration of the device, but for different values of operating parameters. In [2], the kinematic structure of the flow in the initial section of the tube was investigated, and a series of flow temperature measurements at expansion ratios π = 2–6 was performed. In [3], the kinematic flow structure and the evolution of the velocity in the tube along the entire length of the working channel were studied for μ = 0.25–0.26 and π = 2–4 (μ is the ratio of the flow rate through the cold tube outlet to the inlet flow rate and π is the ratio of the total pressures at the tube inlet and tube outlets). In [4], the velocity coefficients in the guide vane inlet slits and the temperature variation coefficients at the tube outlets in a wide range of determining flow parameters (μ = 0.2–0.8 and π = 2–7) were analyzed. The following results were obtained.
Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk 63
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