The effects of low-profile vortex generators on flow in a transonic fan-blade cascade

The demand of further increased bypass ratios for turbofan engines will lead to low pressure turbines with larger diameter and lower rotational speed in conventional high-bypass aeroengine architectures. Due to that, it is necessary to guide the flow leaving the high pressure turbine to the low pressure turbine at a larger diameter without any severe loss generating separation or flow disturbances. To reduce costs and weight this turbine duct has to be as short as possible. This results in superaggressive (very high diffusion) S-shaped geometries where the boundary layers are not able to withstand the strong adverse pressure gradient, which results in flow separation. This paper describes the flow through a fully separated duct as a baseline configuration. In a next step the influence of passive flow control devices onto this separation has been investigated. Therefore, low-profile vortex generators were applied within the first bend of this S-shaped intermediate turbine diffuser in order to energize the boundary layer and further reduce or even suppress the occurring separation. This configuration was investigated downstream a transonic turbine stage. Measurements were performed by means of five-hole-probes, static wall pressure taps, and oil flow visualization at the duct endwalls. For a better understanding of the flow behavior the vortex generators were also investigated in a two-dimensional rectangular S-shaped duct using the same Mach number level. Results showed that the vortex generators reduce the separation in the 2D-duct but have no distinct influence on the separation within the turbine duct due to wakes as well as strong secondary flow effects.

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Radial Decomposition of Blade Vibration to Identify a Stall Flutter Source in a Transonic Fan

Journal of Turbomachinery ◽

10.1115/1.4044484 ◽

2019 ◽

Vol 141 (10) ◽

Author(s):

Q. Rendu ◽

M. Vahdati ◽

L. Salles

Keyword(s):

Pressure Fluctuations ◽

Navier Stokes ◽

Local Vibration ◽

Blade Vibration ◽

Nonlinear Solver ◽

Low Mass ◽

Stall Flutter ◽

Fan Blade ◽

Unstable Oscillation ◽

Transonic Fan

Abstract This paper investigates the three dimensionality of the unsteady flow responsible for stall flutter instability. Nonlinear unsteady Reynolds-averaged Navier–Stokes (RANS) computations are used to predict the aeroelastic behavior of a fan blade at part speed. Flutter is experienced by the blades at low mass flow for the first flap mode at nodal diameter 2. The maximal energy exchange is located near the tip of the blade, at 90% span. The modeshape is radially decomposed to investigate the main source of instability. This decomposition method is validated for the first time in 3D using a time-marching nonlinear solver. The source of stall flutter is finally found at 65% span where the local vibration induces an unstable oscillation of the shock-wave of large amplitude. This demonstrates that the radial migration of the pressure fluctuations must be taken into account to predict stall flutter.

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Flow Field Analysis and Nearfield Acoustic Signature Reduction of a Stationary Fan Blade Array

Journal of Fluids Engineering ◽

10.1115/1.4049116 ◽

2020 ◽

Author(s):

Syed Qasim Zaheer ◽

Peter Disimile

Keyword(s):

Flow Field ◽

Vortex Shedding ◽

Leading Edge ◽

Pressure Side ◽

Validation Data ◽

Array Configuration ◽

Blade Cascade ◽

Fan Blade ◽

The Impact ◽

Blade Leading Edge

Abstract A highly cambered and loaded stationary fan blade cascade of an in-service centrifugal fan is analyzed in this research work at flow conditions corresponding to design point operation of subject fan. The configuration of enclosed blade cascade includes upstream and downstream ducts. A preliminary analysis of flow variables and nearfield acoustic spectra is carried out experimentally which then provided boundary conditions and validation data for an extensive numerical analysis using Embedded Large Eddy Simulation turbulence model in ANSYS Fluent 19.0 ® environment. The comprehensive analysis of flow field and nearfield aeroacoustics of blade array configuration reveals vortex shedding from blade leading edge and its interaction with pressure side surface of adjacent blade becomes one of major source in the aeroacoustics signature of blade array. The vortex shedding frequency and the frequency of upstream turbulence interaction with blade leading edge are identified. A novel method of placing rectangular cavity on pressure side of blade array to suppress the impact of impingement of leading-edge vortex via cavity acoustic wave is explored. The numerical results reveal a reduction in noise by 6dB encouraging the efficacy of this method as a passive technique to reduce aeroacoustics signature of researched blade array configuration.

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Optimization of a Fan Blade Cascade Using the Parametric Flow Solver Turb’Opty

Volume 2: Fora ◽

10.1115/fedsm2006-98543 ◽

2006 ◽

Cited By ~ 1

Author(s):

S. Moreau ◽

S. Aubert ◽

G. Grondin ◽

P. Ferrand

Keyword(s):

Stokes Equations ◽

Lift Coefficient ◽

Taylor Series Expansion ◽

Navier Stokes ◽

Navier Stokes Equations ◽

Flow Solver ◽

Free Jet ◽

Engine Cooling ◽

Blade Cascade ◽

Fan Blade

The parameterized CFD solver Turb’Opty™, based on a Taylor series expansion to high order derivatives of the solution of the discretized Navier-Stokes equations, has been successfully applied to the full geometric and flow parameterization of an engine cooling fan blade cascade. The coupling of a recently developed genetic algorithm and the post-processor Turb’Post™ has also yielded a multi-objective optimization of the original Valeo airfoil. A representative geometry of the Pareto front has then been prototyped and tested. Significant improvement of the lift coefficient has been obtained at all incidences. Comparisons with direct Turb’Flow™ cascade results have validated the accuracy of the parameterized solutions and shown the same trend as the free-jet measurements.

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Parametic Study of a Fan Blade Cascade Using a New Parametric Flow Solver Turb’Opty

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45116 ◽

2003 ◽

Author(s):

S. Moreau ◽

S. Aubert ◽

M. N’Diaye ◽

P. Ferrand

Keyword(s):

Stokes Equations ◽

Taylor Series Expansion ◽

Navier Stokes ◽

Reference Solution ◽

Navier Stokes Equations ◽

Flow Solver ◽

Engine Cooling ◽

Blade Cascade ◽

Order Expansion ◽

Fan Blade

The newly developed parameterized CFD solver Turb’Opty™, based on a Taylor series expansion to high order derivatives of the solutions of the discretized Navier-Stokes equations, has been successfully applied to the turbulent incompressible flow field of an engine cooling fan blade cascade. Comparisons with the classical CFD results have validated the accuracy of the parameterized solutions obtained by a simple polynomial reconstruction around a reference solution with respect to two different flow parameters for two different cases: a fifth order expansion with respect to these coupled parameters for a frozen turbulence and a first order expansion with respect to each parameter for a variable turbulence. The latter is found to have a better accuracy and a larger range of application. Starting from a reference solution obtained with another commercial code has also been successfully tested. Finally, further industrial perspectives of turbomachinery global optimization are finally demonstrated by coupling this method with a simple genetic algorithm.

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Experimental Reduction of Transonic Fan Forced Response by IGV Flow Control

Volume 6: Turbo Expo 2004 ◽

10.1115/gt2004-53975 ◽

2004 ◽

Cited By ~ 1

Author(s):

S. Todd Bailie ◽

Wing F. Ng ◽

William W. Copenhaver

Keyword(s):

Flow Control ◽

Forced Response ◽

Resonant Response ◽

Compressor Blades ◽

Resonant Amplitude ◽

Engine Order ◽

Blade Vibrations ◽

Fan Blade ◽

Transonic Fan ◽

Bending Response

The main contributor to the high-cycle fatigue of compressor blades is the response to aerodynamic forcing functions generated by an upstream row of stators or inlet guide vanes. Resonant response to engine order excitation at certain rotor speeds can be especially damaging. Studies have shown that flow control by trailing edge blowing (TEB) can reduce stator wake strength and the amplitude of the downstream rotor blade vibrations generated by the unsteady stator-rotor interaction. In the present study, the effectiveness of TEB to reduce forced fan blade vibrations was evaluated in a modern single-stage transonic fan rig. Data was collected for multiple uniform full-span TEB conditions over a range of rotor speed including multiple modal resonance crossings. Resonant response sensitivity was generally characterized by a robust region of strong attenuation. The baseline resonant amplitude of the first torsion mode, which exceeded the endurance limit on the critical blade, was reduced by more than 80% with TEB at 1.0% of the total rig flow. The technique was also found to be modally robust; similar reductions were achieved for all tested modal crossings, including more than 90% reduction of the second LE bending response using 0.7% of the rig flow.

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