Influence of Wake Sweeping Frequency on the Unsteady Flow Characteristics of an Integrated Aggressive Interturbine Duct

Abstract

A dynamic simulation was launched to research the influence of high-pressure turbine (HPT) rotor wake passing frequency on the flow mechanism in an integrated aggressive interturbine duct (AITD). Sweeping rods were adopted to replace the HPT rotors to decouple the influence of its wake from those of other secondary flows. The diameter of the rods (d/s, nondimensionalized by the pitch (s) of the integrated struts at midspan) was 0.10, and their reduced frequency (f) ranged from 0.49 to 1.61. The k–ω SST turbulence model and γ–θ transition model were adopted for the turbulence closure. A 6.3-million-node structured grid was used to meet the grid dependency. Along with increasing f, the intensified circumferential motion of the wake (1) enhances the wake vortex stretching and exhaustion near the hub; (2) promotes the radial inclination of wakes and elongates and narrows the wake vortex band, resulting in increased spacing between the adjacent wake vortices and the weakened vortex interaction. In the high-f cases, the enhanced turbulence intensity in the interval between the adjacent wakes could suppress the separation bubble on LPT-GV in advance, but the elongated and narrowed wake vortices resulted in a substantial reduction in the radial extent and duration of their suppression on the separation bubble. Therefore, the influence of f on the integrated AITD and its parts was bidirectional, and adjusting the sweeping frequency to balance its positive and negative effects could minimize the total loss in the integrated AITD.

Influence of Upstream Sweeping Wake Number on the Unsteady Flow Mechanism in an Integrated Aggressive Intermediate Turbine Duct

“…This paper focuses on the dynamic internal flow in the integrated AITD with different HPT wake numbers, by using CFX Solver with dynamic RANS. Based on the previous research of the authors' team [25,26], the SST turbulence model and γ-θ transition model are used for turbulence closure, because they have strong ability in high-precision boundary layer simulation and can accurately simulate high turbulence dissipation flow. The time term is discretized with a second-order precision backward difference scheme, while the convection term is discretized with a second-order precision upwind scheme.…”

“…As the N increases, this migration effect weakens; in the N = 14 case, wake vortices near the casing in section B2 are almost squeezed together, while in the N = 42 case, there are still obvious gaps between wake vortices near the casing. This is because the increasing wake number enhances the blocking effect and thus weakens the radial pressure gradient in the AITD [25], resulting in a suppression of the radial migration of wake vortices to some extent. The convergence of wake vortices near the casing enhances vortex mixing and dissipation in this region.…”

“…Zhou et al [24] studied the coupling effect of upstream wake and inlet streamwise vortex on the internal flow of the ITD, and pointed out that the distance between them has a major effect on the flow pattern and aerodynamic loss of the ITD. The authors' team [25,26] studied the influence of sweeping frequency and wake intensity on the inner stream of the integrated AITD and the boundary layer of the integrated LPT-GV, and indicated that as wake intensity decreases or the wake reduced frequency increases, the wake skewness increases and the wake width narrows, which can make the duration and radial range of the flow separation inhibition by wakes decrease, resulting in an increase in separation loss. Based on these works, this paper will focus on the effect of HPT wake number on the flow field in the integrated AITD, especially on the internal flow in the integrated LPT-GV passage, and explore the wake number that minimizes the flow loss inside the integrated LPT-GV to guide the selection of upstream high-pressure turbine blade numbers and their matching design with the integrated AITD.…”