Numerical Investigation of Aerothermal Characteristics of the Blade Tip and Near-Tip Regions of a Transonic Turbine Blade

Abstract

In modern gas turbine engines, the blade tips and near-tip regions are exposed to high thermal loads caused by the tip leakage flow. The rotor blades are therefore carefully designed to achieve optimum work extraction at engine design conditions without failure. However, very often gas turbine engines operate outside these design conditions which might result in sudden rotor blade failure. Therefore, it is critical that the effect of such off-design turbine blade operation be understood to minimize the risk of failure and optimize rotor blade tip performance. In this study, the effect of varying the exit Mach number on the tip and near-tip heat transfer characteristics was numerically studied by solving the steady Reynolds averaged Navier Stokes (RANS) equation. The study was carried out on a highly loaded flat tip rotor blade with 1% tip gap and at exit Mach numbers of Mexit = 0.85 (Reexit = 9.75 × 105) and Mexit = 1.0 (Reexit = 1.15 × 106) with high freestream turbulence (Tu = 12%). The exit Reynolds number was based on the rotor axial chord. The numerical results provided detailed insight into the flow structure and heat transfer distribution on the tip and near-tip surfaces. On the tip surface, the heat transfer was found to generally increase with exit Mach number due to high turbulence generation in the tip gap and flow reattachment. While increase in exit Mach number generally raises he heat transfer over the whole blade surface, the increase is significantly higher on the near-tip surfaces affected by leakage vortex. Increase in exit Mach number was found to also induce strong flow relaminarization on the pressure side near-tip. On the other hand, the size of the suction surface near-tip region affected by leakage vortex was insensitive to changes in exit Mach number but significant increase in local heat transfer was noted in this region.

Numerical investigation of high pressure turbine blade tip-shaping effects on the aerothermal and dynamic performance

“…The combination of the squealer seal and streamwise rib structure can control the tip leakage loss effectively, and the effect of conjugate heat transfer between the blade tip and high temperature gas is decreased. These findings are consistent with the earlier research works Azad, Han, Bunker and Lee, 2002;Lomakin et al 2013;Arisi et al, 2015).…”

“…These findings are consistent with the earlier research works (Azad, Han and Robert, 2000; Azad, Han, Bunker and Lee, 2002; Lomakin et al . 2013; Arisi et al , 2015).…”

“…The inner coolant part is modeled on the basis of the cooling structure of rotor blade, which is the passage of cooing air. For the outer mainstream, the main inlet and main outlet are posited one-chord upstream and downstream along the blade LE and TE, respectively (Arisi et al , 2015). The computational model of mainstream is obtained according to the path of high temperature gas and the arrangement of rotor blade.…”

“…For the prism elements, the height of first mesh is 0.01 and the number of layers is more than 11, which ensures that the wall grid y + values (30‒80) can satisfy the requirement of applied turbulent model (Yu et al , 2011). To improve both the calculation precision and efficiency, it is essential to perform a grid independence analysis (Figure 4) (Arisi et al , 2015). The average tip HTCs of several mesh cells are compared.…”

Numerical analysis of the aerodynamic performance and excitation forces in a transonic turbine cascade with flat-tip and squealer-tip blades

“…Arisi et al. 5 numerically studied the effects of varying the exit Mach number on the tip and near-tip heat transfer characteristics and obtained that reattachment and shock boundary layer interaction play a significant role in increasing the heat load on the blade tip. As for the effects of tip structure, Kim et al.…”