Aerodynamic Optimization of a Winglet-Shroud Tip Geometry for a Linear Turbine Cascade

Abstract

This paper presents a continued study on a previously investigated novel winglet-shroud (WS) (or partial shroud) geometry for a linear turbine cascade. Various widths of double-side winglets (DSW) and different locations of a partial shroud are considered. In addition, both a plain tip and a full shroud tip are applied as the datum cases which were examined experimentally and numerically. Total pressure loss and viscous loss coefficients are comparatively employed to execute a quantitative analysis of aerodynamic performance. The effectiveness of various widths (w) of DSW set at 3%, 5%, 7%, and 9% of the blade pitch (p) is numerically investigated. Skin-friction lines on the tip surface indicate that different DSW cases do not alter flow field features including the separation bubble and reattachment flow within the tip gap region, even for the case with the broadest width (w/p = 9%). However, the pressure side extension of the DSW exhibits the formation of separation bubble, while the suction side platform of the DSW turns the tip leakage vortex (TLV) away from the suction surface (SS). Meanwhile, the horse-shoe vortex (HV) near the casing is not generated even for the case with the smallest width (w/p = 3%). As a result, both the tip leakage and the upper passage vortices are weakened and further dissipated with wider w/p in the DSW cases. Larger width of the DSW geometry is indeed able to improve the aerodynamic performance, but only to a slight degree. With the w/p increasing from 3% to 9%, the mass-averaged total pressure loss coefficient over an exit plane is reduced by only 2.61%. Therefore, considering both the enlarged (or reduced) tip area and the enhanced (or deteriorated) performance compared to the datum cases, a favorable width of w/p = 5% is chosen to design the WS structure. Three locations for the partial shroud (linkage segment) are devised, locating them near the leading edge, in the middle and close to the trailing edge, respectively. Results demonstrate that all three cases of the WS design have advantages over the DSW arrangement in lessening the aerodynamic loss, with the middle linkage segment location producing the optimal effect. This conclusion verifies the feasibility of the previously studied WS configuration.

Experimental and Numerical Investigations for Dual−Cavity Tip Aerodynamic Performance in the Linear Turbine Cascade

“…The flow fields for analysis in this research are solved using ANSYS CFX v14.0. Referring to the previous studies on the tip leakage flow problems of Zhang [10] and Maral [14], Menter's SST turbulence model [15] has been used to approximate the turbulent viscosity in the present study. The fluid mesh has a first layer grid width of 2 × 10 −6 m and the Y plus value is 0.02~2 on the blade.…”

“…Zhang [10] investigated a new winglet-shroud geometry and derived the conclusions that the winglet-shroud design is able to minimize aerodynamic losses due to the common winglet structure when a linkage exists in the middle streamwise position of the winglet. Zhou [11] also designed a multi-parameter control-based tip geometry modeling method based on the winglet structure and obtained a new tip geometry structure with maximum efficiency using a multi-island genetic algorithm.…”

Investigations into heat transfer and film cooling effect on winglet-squealer tips in a turbine stage

“…Zhong and Zhou 13 found that the leakage loss in winglet-squealer tip is reduced significantly as compared with the conventional squealer tip. By using the optimization strategies, Maesschalck et al 14 Zhang et al 15 Caloni et al 16 and Zhou et al 17 presented the optimized geometries of winglet and novel designs of squealer-winglet tip, which have shown promising benefits in aerodynamic performance improvement in the tip region. For the heat transfer and film cooling effect, Papa et al, 18 Silva and Tomita, 19 Zhou et al, 20 and Yan et al 21 reported that the winglet extension is beneficial for the heat transfer reduction as compared with the flat tip and conventional squealer tip.…”

Parametric study of rotor tip squealer geometry on the aerodynamic performance of a high subsonic axial compressor stage

“…in real products. Relevant researches are very active in axial turbines [1][2][3][4], but comparably rare in axial compressors. Different tip geometry (e.g., crown tip, winglet etc.)…”