Hysteresis phenomenon in cavitating flow past a tandem of cylinders
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CUCIUC, Tudor. Hysteresis phenomenon in cavitating flow past a tandem of cylinders. In: Materials Science and Condensed Matter Physics, Ed. 8-th Edition, 12-16 septembrie 2016, Chişinău. Chişinău: Institutul de Fizică Aplicată, 2016, Editia 8, p. 346. ISBN 978-9975-9787-1-2.
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Materials Science and Condensed Matter Physics
Editia 8, 2016
Conferința "International Conference on Materials Science and Condensed Matter Physics"
8-th Edition, Chişinău, Moldova, 12-16 septembrie 2016

Hysteresis phenomenon in cavitating flow past a tandem of cylinders


Pag. 346-346

Cuciuc Tudor
 
Institute of Applied Physics, Academy of Sciences of Moldova
 
Disponibil în IBN: 6 august 2019


Rezumat

The appearance and development of cavitation in various hydrodynamic systems may substantially affect their hydrodynamic characteristics [1]. In complex hydrodynamic systems (blockage, body systems), the flow is affected by the hydrodynamic interference of the cavitation zone with the system's elements, or with other cavitation zones. Thus, once a critical value of the cavitation number, σcr, supercavitation occurring downstream of a body placed into the channel may prevent the mass flow rate variation through a flow choking phenomenon [2]. For the case of a cavitational flow over a couple of cylinders [3] the choking phenomenon was observed for two values of the cavitation number σcr. It was also observed that in such systems the flow pseudo choking phenomenon, accompanied by a hysteresis phenomenon. The paper analyzes the particularities of the choking phenomenon in cavitational flow over a tandem of cylinders, with specific emphasis on the pseudo choking phenomenon [3] supported by the hysteresis phenomenon. The cavitation development phases are dependent on the distance between the cylinders, L, and the degree of flow blockage, d/H. In the ranges L < Lcr1 = 3.45, for d/H < 0.22 and L < Lcr2 =2.20 for 0.22 < d/H < 0.40, the supercavitation zone extends monotonously with the decrease in the cavitation number, does not depend on its generation method, and σcr = σcrmin. If L > Lcr, cavitation develops separately, behind each cylinder. The most important flow modifications are concentrated close to the downstream cylinder. The cavitational flow behind the second cylinder extends rapidly reaching the supercavitation regime at much higher cavitation number values than those observed in the cavitational flow past a singular cylinder, or past tandem of cylinders at distances L< Lcr and identical flow blockage ratio. The reason for the sudden change in the cavitation zone is the cavity vortices that, while maintaining shape as they move around the second cylinder (fig. 1a), they substantially increase the flow blockage ratio in the downstream cylinder region. Depending on L and d/H, either the flow including the  zone of supercavitation behind the second cylinder until the choking phenomenon occurs (σcrmax), or the flow at a certain value of the cavitation number σ=σL pseudo choking phenomenon) suddenly changes into supercavitational flow behind the upstream cylinder (fig. 1b). In terms of the ΔP(Q) characteristic curve (fig. 2), these transformations occurs at points A(σLA) and C(σLC). The hysteresis phenomenon observed in fig. 2 (the hysteretic loop DABC) occurs under conditions where the periodic cavity vortices generated by the upstream cylinder may ensure the development of the supercavitation regime after the second cylinder (an increase in the mass flow rate), while in the supercavitation regime behind the first cylinder, the second cylinder is intergally immersed in this zone (a decrease in the mass flow rate).