Vrednotenje kavitacijskih in tokovnih razmer v postaji z majhno režo

Poljanšek, Žiga (author), Dular, Matevž (mentor)

V hidrodinamiki se inercialna kavitacija pojavlja, ko se na majhni razdalji izrazito spremeni hitrost tekočine in privede do znižanja lokalnega tlaka. Kavitacija je v večini nezaželen pojav, katere učinki so erozija, prekomeren hrup, vibracije in motnje režima toka. Obravnavali smo pojav kavitacije v objektu z majhno režo, ki smo ga izdelali za potrebe večjega tujega podjetja. Objekt nam je omogočal, da s hitro kamero posnamemo nastalo obliko kavitacije. Dobljene posnetke smo nato preučili in računalniško obdelali. Rezultate smo predstavili v obliki konturnih diagramov za srednjo vrednost sivine in standardni raztros sivine ter v obliki frekvenčnih diagramov. Analizirali smo hitrosti udarnih valov in iskali ponovljive vzorce v dinamiki tekočine, ki kavitira. Ugotovili smo, da na razširjenost kavitacije vpliva predvsem tlak na izstopu iz šobe, ki vpliva tudi na frekvenco trganja kavitacijskih struktur, kjer padec tlaka povzroči znižanje frekvence. Z analizo udarnega vala smo ugotovili, da dosega hitrosti tudi do 400 m/s, njegovo obnašanje pa je precej kaotično, nepredvidljivo in brez kakršnihkoli vzorcev. Pri analizi »kavitacijske rože« je moč opaziti prisotnost tlačnega vala na robu kavitacije in njegov vpliv na porušitev kavitacijskih struktur.

• Language: Slovenian
• Keywords: kavitacija, intenziteta, frekvenca trganja, udarni val, kavitacijska roža, kolaps
• Work type: Bachelor thesis/paper
• Organization: FS - Faculty of Mechanical Engineering
• Year: 2018
• PID: 20.500.12556/RUL-104833
• Publication date in RUL: 12.10.2018

POLJANŠEK, Žiga, 2018, Vrednotenje kavitacijskih in tokovnih razmer v postaji z majhno režo [online]. Bachelor’s thesis. [Accessed 25 March 2025]. Retrieved from: https://repozitorij.uni-lj.si/IzpisGradiva.php?lang=eng&id=104833

Secondary language

• Language: English
• Title: Evaluation of cavitation and flow conditions in a station with a small slit

Abstract

In hydrodynamics, the inertial cavitation occurs when the speed of fluid changes drastically at a small distance, which leads to reduced local pressure. Cavitation is, in most cases, an undesirable phenomenon, the effects of which are erosion, excessive noise, vibration, and flow disorder. We discussed the occurrence of cavitation in a test model with a small nozzle, which we designed for the needs of major foreign company. The model allowed us to record the formation of cavitation with a fast camera. Obtained images were then examined and processed with a computer. The results were presented in the form of contour diagrams for the mean value of the greys, the standard deviation of the greys and in the form of frequency diagrams. We analysed the velocity of shock waves and looked for repeatable patterns in the dynamics of cavitating fluids. We found that the spread of cavitation is dependent mainly by the exit pressure from the nozzle, which also affects the rupture frequency of cavitation structures, in which the pressure drop causes a decrease in the frequency. By analysing shock waves, we found that its behaviour was rather chaotic, unpredictable, and without any patterns, which achieved speeds up to 400 m /s. In the analysis of the "cavitation flower" we observed the presence of a pressure wave on the edge of cavitation and its effect on the collapse of cavitation structures.

• Keywords: cavitation, intensity, rapture frequency, shock wave, cavitation flower, collapse