Effects of Upstream Wakes on the Boundary Layer Over a Low-Pressure Turbine Blade

Vincentiis, Luca De; Ðurović, Kristina; Lengani, Davide; Simoni, Daniele; Pralits, Jan O.; Henningson, Dan S.; Hanifi, Ardeshir

doi:10.1115/1.4056108

Cited by 7 publications

(1 citation statement)

References 31 publications

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“…Note that neither of the scenarios considered in this work are comparable to turbulent inflow conditions found in, for example, steam and gas turbines that are studied in detail elsewhere (Merrill & Peet 2017; De Vincentiis et al. 2023). The considered range of disturbance amplitudes is relatively small compared with the turbulence intensities up to 1 %–3 % routinely encountered in many aeronautical applications.…”

Section: Direct Numerical Simulations Of Dynamic Stall Onsetmentioning

confidence: 92%

Direct numerical simulations of an airfoil undergoing dynamic stall at different background disturbance levels

Kern,

Blanco,

Cavalieri

et al. 2024

J. Fluid Mech.

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Thin airfoil dynamic stall at moderate Reynolds numbers is typically linked to the sudden bursting of a small laminar separation bubble close to the leading edge. Given the strong sensitivity of laminar separation bubbles to external disturbances, the onset of dynamic stall on a NACA0009 airfoil section subject to different levels of low-amplitude free stream disturbances is investigated using direct numerical simulations. The flow is practically indistinguishable from clean inflow simulations in the literature for turbulence intensities at the leading edge of ${Tu} = 0.02\,\%$ . At slightly higher turbulence intensities of ${Tu} = 0.05\,\%$ , the bursting process is found to be considerably less smooth and strong coherent vortex shedding from the laminar separation bubble is observed prior to the formation of the dynamic stall vortex (DSV). This phenomenon is considered in more detail by analysing its appearance in an ensemble of simulations comprising statistically independent realisations of the flow, thus proving its statistical relevance. In order to extract the transient dynamics of the vortex shedding, the classical proper orthogonal decomposition method is generalised to include time in the energy measure and applied to the time-resolved simulation data of incipient dynamic stall. Using this technique, the dominant transient spatiotemporally correlated features are distilled and the wave train of the vortex shedding prior to the emergence of the main DSV is reconstructed from the flow data exhibiting dynamics of large-scale coherent growth and decay within the turbulent boundary layer.

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Section: Direct Numerical Simulations Of Dynamic Stall Onsetmentioning

confidence: 92%

Direct numerical simulations of an airfoil undergoing dynamic stall at different background disturbance levels

Kern,

Blanco,

Cavalieri

et al. 2024

J. Fluid Mech.

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On the reduction of the noise in a low-pressure turbine cascade associated with the wavy leading edge

Han,

Zhang,

et al. 2023

Physics of Fluids

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The low-pressure turbine (LPT) has become a potential noise source for future ultra-high by-pass ratio engines. In this paper, the feasibility and mechanism of wavy leading edge (WLE) noise control in the LPT cascade model are analyzed. The flow field and acoustic data are obtained with the large eddy simulation and Ffowcs Williams–Hawkings methods, which are validated using experimental data. The acoustic results are compared for different models; the maximum noise reduction can achieve 8.6 and 3.7 dBA in the frequency bands of FR#2 (315–4000 Hz) and FR#4 (6300–16 000 Hz), respectively; the noise reduction does not vary proportionally to the WLE parameter. The noise source is identified in the baseline model, and then the effect of WLE amplitude and wavelength on the noise source and its control on pressure fluctuations are evaluated. The pressure statistics demonstrate that WLE with a smaller wavelength and a larger amplitude can reduce the impingement of stator wakes on the leading edge of the rotor and stabilize the pressure fluctuation. To analyze the mechanism of WLEs on noise control, the pressure spectrum in terms of amplitude and coherence coefficient is utilized to explain the excellent noise performance of the WLE model in FR#2. The proposed similarity coefficient of coherence can quantify the destructive interference level and thus the coherence characteristics of the sound source. Generally, the noise reduction level can be predicted by the combination of the similarity coefficient and the amplitude spectrum of the pressure fluctuations for the WLE models.

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Compressibility effects on the flow past a T106A low-pressure turbine cascade

Sengupta,

Sundaram

2023

Physics of Fluids

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The present numerical investigation delves into the intricate interplay between Mach number (Ms), flow characteristics, and vorticity dynamics within a T106A low-pressure turbine (LPT) blade passage. The two-dimensional (2D) compressible Navier–Stokes equations are solved using a high-accuracy, dispersion relation preserving methodology, which is validated against benchmark direct numerical simulations. Four Ms ranging from 0.15 to 0.30 are computed in order to display the intricate response of compressibility on the separation-induced transition process. The emergence and evolution of unsteady separation bubbles along the suction surface of the T106A blade are explored, revealing a growing trend with Ms. The time-averaged boundary layer parameters evaluated along the suction surface display a delayed separation with a smaller streamwise extent with increasing Ms. However, an overall increase in the blade profile loss and a decrease in turbulent mixing are observed with increasing Ms, suggesting a detrimental effect on LPT performance. Applying the compressible enstrophy transport equation (CETE) to the flow in a T106A blade passage reveals that while a linear relationship exists between Ms and certain CETE budget terms, other terms have a nuanced dependency, which paves the way for future investigations into the role of compressibility on enstrophy dynamics.

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Effects of Upstream Wakes on the Boundary Layer Over a Low-Pressure Turbine Blade

Cited by 7 publications

References 31 publications

Direct numerical simulations of an airfoil undergoing dynamic stall at different background disturbance levels

Direct numerical simulations of an airfoil undergoing dynamic stall at different background disturbance levels

On the reduction of the noise in a low-pressure turbine cascade associated with the wavy leading edge

Compressibility effects on the flow past a T106A low-pressure turbine cascade

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