On the Unsteady Aerodynamics of a High-Speed Turbine with Squealer Blade Tips

Cernat, Bogdan C.; Pátý, Marek; Lavagnoli, Sergio

doi:10.2514/6.2018-4434

Cited by 4 publications

(2 citation statements)

References 19 publications

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“…The time-resolved aerodynamic field was interrogated by traversing double-head Kulite sensor rakes (20 radial × 8 circumferential = 160 measurement points). The probe detected the blade-to-blade flow variations up to frequencies in excess of 50 kHz with a precision of ±0.01% of P 01 (0.1 mbar) [22]. Miniaturized single-hole probes were employed in "virtual three-hole probe" mode [23], emulating the yaw-sensitivity of real three-sensor probes by applying a probe rotation in three consecutive tests for each investigation point.…”

Section: Measurement Setupmentioning

confidence: 99%

“…Conversely, the flow structures which show a steady behaviour in the rotor relative frame represent the rotor modes. The total energy content of the rotor-and vane-dependent periodicities can therefore be computed by knowing their position in the matrix [22]. All the remaining modes result non-stationary in both reference frames and are addressed as vane-rotor interactions.…”

Section: Modal Analysismentioning

confidence: 99%

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Characterization of the Unsteady Aerodynamics of Optimized Turbine Blade Tips through Modal Decomposition Analysis

Cernat

Lavagnoli

2019

IJTPP

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The present research focused on the analysis of the leakage flows developing from advanced blade tip geometries. The aerodynamic field of a contoured blade tip and of a high-performance rimmed blade were investigated against a baseline squealer rotor. Time-resolved numerical predictions were combined with high-frequency pressure measurements to characterize the tip leakage flow of each tip design. High spatial and temporal resolution measurements provided a detailed representation of the unsteady flow in the near-tip region and at the stage outlet. Numerical computations, based on the nonlinear harmonic method, were employed to assess the unsteady blade row interactions and identify the loss generation mechanisms depending on the tip design. The space- and time-resolved flow field was analysed by modal decomposition to identify the main periodicities of the near-tip and outlet flow and classify the most relevant sources of aerodynamic unsteadiness and entropy generation across the stage.

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Section: Measurement Setupmentioning

confidence: 99%

Section: Modal Analysismentioning

confidence: 99%

Characterization of the Unsteady Aerodynamics of Optimized Turbine Blade Tips through Modal Decomposition Analysis

Cernat

Lavagnoli

2019

IJTPP

Self Cite

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Design and Testing of a Miniaturized Five-Hole Fast Response Pressure Probe With Large Frequency Bandwidth and High Angular Sensitivity

Boufidi

Alati

Fontaneto

et al. 2019

Journal of Engineering for Gas Turbines and Power

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A miniaturized five-hole fast response pressure probe is presented, and the methods for the aerodynamic design and performance characterization are explained in detail. The probe design is aimed for three-dimensional (3D) time-resolved measurements in turbomachinery flows, therefore requiring high frequency response and directional sensitivity. It features five encapsulated piezoresistive pressure transducers, recessed inside the probe hemispherical head. Theoretical and numerical analyses are carried out to estimate the dynamic response of the pressure tap line-cavity systems and to investigate unsteady effects that can influence the pressure readings. A prototype is manufactured and submitted to experimental tests that demonstrate performance in line with the theoretical and numerical predictions of the dynamic response: the natural frequency of the central and lateral taps extends to 200 and 25 kHz, respectively. An aerodynamic calibration is also performed at different Reynolds and Mach numbers. The probe geometry offers a good angular sensitivity in a ± 30 deg incidence range, while a frequency analysis reveals the presence of pressure oscillations related to vortex shedding at large angles of attack.

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A Novel Vortex Identification Technique Applied to the 3D Flow Field of a High-Pressure Turbine

Pátý

Lavagnoli

2020

Journal of Turbomachinery

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The efficiency of modern axial turbomachinery is strongly driven by the secondary flows within the vane or blade passages. The secondary flows are characterized by a complex pattern of vortical structures that origin, interact, and dissipate along the turbine gas path. The endwall flows are responsible for the generation of a significant part of the overall turbine loss because of the dissipation of secondary kinetic energy and mixing out of nonuniform momentum flows. The understanding and analysis of secondary flows requires a reliable vortex identification technique to predict and analyze the impact of specific turbine designs on the turbine performance. However, the literature shows a remarkable lack of general methods to detect vortices and to determine the location of their cores and to quantify their strength. This paper presents a novel technique for the identification of vortical structures in a general 3D flow field. The method operates on the local flow field, and it is based on a triple decomposition of motion proposed by Kolář. In contrast to a decomposition of velocity gradient into the strain and vorticity tensors, this method considers a third, pure shear component. The subtraction of the pure shear tensor from the velocity gradient remedies the inherent flaw of vorticity-based techniques, which cannot distinguish between rigid rotation and shear. The triple decomposition of motion serves to obtain a 3D field of residual vorticity whose magnitude is used to define vortex regions. The present method allows to locate automatically the core of each vortex, to quantify its strength, and to determine the vortex bounding surface. The output may be used to visualize the turbine vortical structures for the purpose of interpreting the complex three-dimensional viscous flow field and to highlight any case-to-case variations by quantifying the vortex strength and location. The vortex identification method is applied to a high-pressure turbine with three optimized blade tip geometries. The 3D flow field is obtained by computational fluid dynamics (CFD) computations performed with Numeca FINE/Open. The computational model uses steady-state Reynolds-averaged Navier–Stokes (RANS) equations closed by the Spalart-Allmaras turbulence model. Although developed for turbomachinery applications, the vortex identification method proposed in this work is of general applicability to any three-dimensional flow field.

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On the Unsteady Aerodynamics of a High-Speed Turbine with Squealer Blade Tips

Cited by 4 publications

References 19 publications

Characterization of the Unsteady Aerodynamics of Optimized Turbine Blade Tips through Modal Decomposition Analysis

Characterization of the Unsteady Aerodynamics of Optimized Turbine Blade Tips through Modal Decomposition Analysis

Design and Testing of a Miniaturized Five-Hole Fast Response Pressure Probe With Large Frequency Bandwidth and High Angular Sensitivity

A Novel Vortex Identification Technique Applied to the 3D Flow Field of a High-Pressure Turbine

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