Validação de equações para cálculo de labirinto do tipo plano usados em turbinas hidráulicas

Abstract

The hydraulic turbine is a driving machine that converts hydraulic power into mechanical power. There is some fluid loss in the hydraulic machine (turbines) due to a pressure difference between its inlet, outlet and rotor cover. This loss occurs through the labyrinths, which are parts or devices used to assure sealing, or some small loss of specific fluid existing between the fixed and the mobile portions of the turbomachinery. This study focuses on the straight-through type, also known as plane labyrinths in the Francis hydraulic turbines, which is not largely discussed in literature. Through bibliographic research, the types of labyrinths and the equations related to the fluid flow (Q), the pressure difference (head loss) (∆p), the flow coefficient (μ), the fluid jet contraction coefficient and / or friction and / or the power supply (α) and the resistance coefficient (λ) have been studied. After surveying the equations, tests were carried out on a labyrinth test bench on a hydraulic turbine rotor patented by the Federal University of Minas Gerais, under registration BR 10 2019 013739 8 INPI/2019, Brazil (UFMG, 2019) and installed in the UFMG Hydraulic Research Center (CPH). The equipment placed in the CPH simulates conditions in a Francis turbine labyrinth, assessing the pressure variation in the labyrinth according to the flow variation and the rotation of the machinery rotor. Real operating conditions were simulated with the aim of comparing the coefficients (μ, α and λ) obtained in the tests with theoretically calculated values described in literature. The results showed that the values of (μ) and (α) obtained in the tests are close to values referred to in bibliographic research and theoretically calculated. On the contrary, the coefficient ((λ) obtained in the tests was quite different from the calculated values. It is believed that Taylor’s vortexes and other phenomena may have influenced the ((λ) results. The conclusion is that it is important to understand the types of labyrinths and the equations that describe each one, so that they are sized correctly for each application.