Boundary layer transition Turbulence modelling Endwall loss Leakage

ﻻیﻪ ﻣﺮﺯی ﺩﺭ ﺍﻫﻤیﺖ ﻃﺮﺍﺣی کﻤپﺮﺳﻮﺭﻫﺎ Boundary layer transition • Turbulence modelling • Endwall loss • Leakage loss • Compressor leading edge flow • Turbine trailing edge flow • Effects of small geometrical features • Unsteady losses � � � �

Boundary layer transition is influenced by: �Pressure gradient �Reynolds number �Turbulence level �Surface curvature �Surface roughness � 3 D flow

Boundary layer transition • Pressure gradient • Reynolds number • Turbulence level • Surface curvature • Surface roughness • 3 D flow � � �

ENDWALL (or secondary) LOSS Secondary flow and endwall loss in both turbines and � compressors is mainly determined by the thickness and skew of the annulus boundary layers.

BLOCKAGE DEVELOPMENT IN A TRANSONIC, AXIAL COMPRESSOR ROTOR �

Transition modelling �The variety of possible transition mechanisms in Turbomachinery flows makes it difficult to propose the general strategy for numerical simulation. Intuitively, the best solution for the modelling of the transitional boundary layer is the application of Direct Eddy Simulation (DES) or Large Eddy Simulation (LES). However, in LES, which unlike DNS resolves only dynamically important (large) scales, the effect of unresolved small scales is modeled

Transition process in combustion chambers � Generally it is thought that transition is not occurring in combusors. But, it is shown by Paxson and Mayle (1991) that laminar boundary layers can and do exist in flows with extreme turbulence as long as the pressure gradient is favourable. Consequently, in the exit ducts of combustors where a large favourable pressure gradients are obtained, laminar and transitional flows occur with transition being in both direction. . Usually, there is no effect on aerodynamic performance of the combustor unless, as possible in reversecurved exit ducts, the duct is so poorly designed that it separates. Therefore, the main role of transition in combustors is its effect on heat transfer. Since convective heat transfer to the liner walls is significant only in the exit duct, it is only here that one may like to expect the benefits of understanding the role of transition in combustion chambers. Usually a combustor may be considered as a device which is highly turbulent, with constant pressure and low velocity flow condition.

Transition process in turbines (a) flow in high pressure turbines: �

(b) flow in low pressure turbines

Olympus Engine