Effect of Common Blade Tip Squealer Designs in Terms of Tip Clearance Loss Control

Abstract

The increase of new gas turbine’s efficiency is connected with further rise of turbine inlet temperature and sometimes as well pressure. In these conditions, first cooled turbine stages of a gas turbine engine usually consist of freestanding airfoils, which do not use an integrated shroud, to avoid risk of shroud overheating. In order to better control the radial gap leakage flow between the rotating blade tip and turbine casing, special design features of the airfoil tip need to be considered in the design process to meet the best possible stage performance. In the general engineering practice, a blade tip squealer provides opportunities to control tip clearance loss. In this paper several simplified types of the tip squealer design are investigated to determine the most effective loss control. At this stage of the investigation, blade tip cooling was not taken into account, but aerodynamic effects were analysed in detail. Based on the most common designs of the blade tip in the literature, four geometry types were investigated: (i) a flat tip design as the reference baseline solution, (ii) full tip squealer, (iii) partial squealer along the pressure side (PS) wall with a cut-out at the pressure side near the trailing edge (TE) and (iv) partial squealer along the suction side (SS) wall with a cut-out at the suction side near TE. All these cases have been compared among each other for two relative radial gaps (gap to blade height) of 0.6% and 1.36%. The flow calculations were done with a full 3D Navier-Stokes CFD code. For the flat tip and for full squealer designs, numerical results were validated against well-known experimental data measured on the GE-E3 blade cascade test rig found in the open literature. By using the 3D numerical data, the special attention was considered to confirm reliability and predictive credibility of the blade tip flow obtained from the analytical model. The obtained loss values and flow details were compared for all studied cases, providing insight into turbine stage aerodynamics with respect to minimal and maximal radial clearance.

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

“…The results of static pressure ratio distribution are in agreement with the tip and near-tip flow patterns. The similar researches have also been reported in the studies by Yang et al (2010), Azad, Han, Teng and Robert (2000), Lomakin et al (2013) and Ye et al (2015).…”

“…According to the research of Lomakin et al (2013) and Yang et al (2002), the k-ε turbulence model with the scalable wall function is selected in this solution, which is widely used for the simulation of complex flows, for example the secondary flow and the separation flow near the boundary layer (Ye et al, 2015). For the numerical method validation (Wang et al, 2015(Wang et al, , 2018He, 2017;Yan et al, 2017), the blade profile is generated on the basis of the well-known GE-E 3 rotor blade ( first stage) tip section (Timko, 1990).…”

“…Many kinds of turbulence models with corresponding equations are provided for the CFD simulation. According to the research of Lomakin et al . (2013) and Yang et al .…”

“…The optimum value of groove depth is about 2.5 percent of the blade span, and the larger or smaller value is not good for the blade tip flow. Lomakin et al (2013) proposed several tip squealer designs. The partial squealer within rim cut-out at the SS near trailing edge (TE) shows the best result of reduction of tip clearance loss.…”

“…The optimum value of groove depth is about 2.5 percent of the blade span, and the larger or smaller value is not good for the blade tip flow. Lomakin et al . (2013) proposed several tip squealer designs.…”