scholarly journals A global analysis of tonal noise in flows around aerofoils

2014 ◽  
Vol 754 ◽  
pp. 5-38 ◽  
Author(s):  
Miguel Fosas de Pando ◽  
Peter J. Schmid ◽  
Denis Sipp
Keyword(s):  
Global Stability ◽  
Acoustic Radiation ◽  
Global Analysis ◽  
Feedback Loops ◽  
Surface Boundary ◽  
Mean Flow ◽  
Suction Surface ◽  
Stability Analyses ◽  
Pressure Surface ◽  
Linearized Operator

AbstractThe generation of discrete acoustic tones in the compressible flow around an aerofoil is addressed in this work by means of nonlinear numerical simulations and global stability analyses. The nonlinear simulations confirm the appearance of discrete tones in the acoustic spectrum and, for the chosen flow case, the global stability analyses of the mean-flow dynamics reveal that the linearized operator is stable. However, the flow response to incoming disturbances exhibits important transient growth effects that culminate in the onset of aeroacoustic feedback loops, involving instability processes on the suction- and pressure-surface boundary layers together with their cross-interaction by acoustic radiation at the trailing edge. The features of the aeroacoustic feedback loops and the appearance of discrete tones are then related to the features of the least-stable modes in the global spectrum: the spatial structure of the direct modes displays the coupled dynamics of hydrodynamic instabilities on the suction surface and in the near wake. Finally, different families of global modes will be identified and the dynamics that they represent will be discussed.

Unsteady Flow Behavior due to Breakdown of Tip Leakage Vortex in an Axial Compressor Rotor at Near-Stall Condition

2000 ◽  
Author(s):  
Masato Furukawa ◽  
Kazuhisa Saiki ◽  
Kazutoyo Yamada ◽  
Masahiro Inoue
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Surface Boundary ◽  
Pressure Side ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Pressure Surface ◽  
Compressor Rotor

The unsteady flow nature caused by the breakdown of the tip leakage vortex in an axial compressor rotor at near-stall conditions has been investigated by unsteady three-dimensional Navier-Stokes flow simulations. The simulations show that the spiral-type breakdown of the tip leakage vortex occurs inside the rotor passage at the near-stall conditions. Downstream of the breakdown onset, the tip leakage vortex twists and turns violently with time, thus interacting with the pressure surface of the adjacent blade. The motion of the vortex and its interaction with the pressure surface are cyclic. The vortex breakdown causes significant changes in the nature of the tip leakage vortex, which result in the anomalous phenomena in the time-averaged flow fields near the tip at the near-stall conditions: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing wall pressure trough corresponding to the leakage vortex, large spread of the low-energy fluid accumulating on the pressure side, and large pressure fluctuation on the pressure side. As the flow rate is decreased, the movement of the tip leakage vortex due to its breakdown becomes so large that the leakage vortex interacts with the suction surface as well as the pressure one. The interaction with the suction surface gives rise to the three-dimensional separation of the suction surface boundary layer.

Endwall Loss and Mixing Analysis of a High Lift Low Pressure Turbine Cascade

2012 ◽  
Author(s):  
M. Eric Lyall ◽  
Paul I. King ◽  
Rolf Sondergaard
Keyword(s):  
Low Energy ◽  
Turbulent Shear ◽  
Surface Boundary ◽  
Test Bed ◽  
Mean Flow ◽  
Suction Surface ◽  
High Lift ◽  
Vortical Structures ◽  
Surface Separation ◽  
The Mean

A high lift LPT profile designated L2A is used as a test bed for studying the origin of endwall mixing loss and the role of vortical structures in loss development. It is shown analytically and experimentally that the mixing forces within the endwall wake can be decoupled into either mean flow or turbulent forces, and can be further classified as either reversible or irreversible. Among the irreversible forces, mean flow shear is negligible compared to turbulent shear, suggesting that turbulence dissipation is the dominant cause of loss generation. As a result, the mean flow components of the vortical structures do not generate significant mixing losses. Rather than mixing effects, the mean flow of the vortices cause the suction surface boundary layer to separate inside the passage, thereby generating the large low energy regions typical of endwall flows. Losses are generated as the low energy regions mix out. This vortex separation effect is demonstrated with an experiment using a profile fence and pressure surface modification near the endwall. The findings in this paper suggest that profile modifications near the endwall that suppress suction surface separation may provide loss reductions additive to those that weaken vortical structures, such as endwall contouring.

Inlet Distortion Generated Periodic Aerodynamic Rotor Response

1990 ◽  
Vol 112 (2) ◽  
pp. 298-307 ◽  
Author(s):  
S. R. Manwaring ◽  
S. Fleeter
Keyword(s):  
Rotor Blade ◽  
Amplitude Ratio ◽  
Unsteady Aerodynamics ◽  
Mean Flow ◽  
Suction Surface ◽  
Unsteady Pressure ◽  
Pressure Surface ◽  
Inlet Distortion ◽  
Loading Level ◽  
Forcing Function

Fundamental inlet distortion-generated rotor blade row unsteady aerodynamics, including the effects of both the detailed aerodynamic forcing function for the first time and steady loading are experimentally investigated in an extensively instrumented axial-flow research compressor. A two-per-rev forcing function with three gust amplitude ratios is generated. On the rotor blade pressure surface, the unsteady pressure nondimensionalization compresses the magnitude data with mean flow incidence angle. This is not the case on the higher camber suction surface. These pressure surface unsteady data are primarily affected by the steady loading level, whereas the suction surface unsteady data are a function of the steady loading level and distribution as well as the gust amplitude ratio. In addition, a design inlet distortion blade surface unsteady pressure correlation is considered.

Film Cooling on a Modern HP Turbine Blade: Part II — Compound-Angle Round Holes

2002 ◽  
Author(s):  
D. Keith Walters ◽  
James H. Leylek ◽  
Frederick A. Buck
Keyword(s):  
Film Cooling ◽  
Density Ratio ◽  
Mean Flow ◽  
High Pressure Turbine ◽  
Suction Surface ◽  
Pressure Surface ◽  
Nominal Density ◽  
High Turbulence ◽  
The Mean ◽  
Compound Angle

A well-tested computational methodology and a companion experimental study are used to analyze the physics of compound-angle, cylindrical-hole film cooling on the pressure and suction surfaces of a modern high-pressure turbine airfoil. A single-passage cascade (SPC) is used to model the blade passage flow experimentally and computationally. Realistic engine conditions, including transonic flow, high turbulence levels, and a nominal density ratio of 1.52, are used to examine blowing ratios of 1.0, 1.5, and 2.0 on the suction surface (SS) and 1.5, 3.0, and 4.5 on the pressure surface (PS). The predicted results agree with experimental trends, and differences are explained in terms of known deficiencies in the turbulence treatment. The mean-flow physics downstream of coolant injection are influenced primarily by a single dominant vortex that entrains coolant and mainstream fluid, and by the effect of convex (SS) or concave (PS) curvature on the coolant jet.

scholarly journals On the receptivity of aerofoil tonal noise: an adjoint analysis

2017 ◽  
Vol 812 ◽  
pp. 771-791 ◽  
Author(s):  
Miguel Fosas de Pando ◽  
Peter J. Schmid ◽  
Denis Sipp
Keyword(s):  
Boundary Layer ◽  
Acoustic Radiation ◽  
Acoustic Scattering ◽  
Surface Boundary ◽  
Frequency Range ◽  
Tonal Noise ◽  
Surface Boundary Layer ◽  
Instability Waves ◽  
Pressure Surface ◽  
Global Modes

For moderate-to-high Reynolds numbers, aerofoils are known to produce substantial levels of acoustic radiation, known as tonal noise, which arises from a complex interplay between laminar boundary-layer instabilities, trailing-edge acoustic scattering and upstream receptivity of the boundary layers on both aerofoil surfaces. The resulting acoustic spectrum is commonly characterised by distinct equally spaced peaks encompassing the frequency range of convectively amplified instability waves in the pressure-surface boundary layer. In this work, we assess the receptivity and sensitivity of the flow by means of global stability theory and adjoint methods which are discussed in light of the spatial structure of the adjoint global modes, as well as the wavemaker region. It is found that for the frequency range corresponding to acoustic tones the direct global modes capture the growth of instability waves on the suction surface and the near wake together with acoustic radiation into the far field. Conversely, it is shown that the corresponding adjoint global modes, which capture the most receptive region in the flow to external perturbations, have compact spatial support in the pressure surface boundary layer, upstream of the separated flow region. Furthermore, we find that the relative spatial amplitude of the adjoint modes is higher for those modes whose real frequencies correspond to the acoustic peaks. Finally, analysis of the wavemaker region points at the pressure surface near 30 % of the chord as the preferred zone for the placement of actuators for flow control of tonal noise.

scholarly journals Inlet Distortion Generated Periodic Aerodynamic Rotor Response

1989 ◽  
Author(s):  
Steven R. Manwaring ◽  
Sanford Fleeter
Keyword(s):  
Rotor Blade ◽  
Amplitude Ratio ◽  
Unsteady Aerodynamics ◽  
Mean Flow ◽  
Suction Surface ◽  
Unsteady Pressure ◽  
Pressure Surface ◽  
Inlet Distortion ◽  
Loading Level ◽  
Forcing Function

Fundamental inlet distortion generated rotor blade row unsteady aerodynamics, including the effects of both the detailed aerodynamic forcing function for the first time and steady loading are experimentally investigated in an extensively instrumented axial flow research compressor. A two-per-rev forcing function with three gust amplitude ratios is generated. On the rotor blade pressure surface, the unsteady pressure nondimensionalization compresses the magnitude data with mean flow incidence angle. This is not the case on the higher camber suction surface. Also, these pressure surface unsteady data are primarily affected by the steady loading level whereas the suction surface unsteady data are a function of the steady loading level and distribution as well as the gust amplitude ratio. In addition, a design inlet distortion blade surface unsteady pressure correlation is considered.

A Comparison of Three Low Pressure Turbine Designs

2012 ◽  
Author(s):  
Christian T. Wakelam ◽  
Reinhard Niehuis ◽  
Martin Hoeger
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Total Pressure ◽  
Maximum Velocity ◽  
Suction Side ◽  
Surface Boundary ◽  
Suction Surface ◽  
Surface Boundary Layer ◽  
Pressure Losses ◽  
Pressure Surface

As part of the current research, three LPT geometries — which were designed with a common pitch, axial chord, inlet angle, and exit Mach number and to create the same nominal level of turning — are compared. Each of the LPT cascades was investigated under a range of Reynolds numbers, exit Mach numbers, and under the influence of a moving bar wake generator. Profile static pressure distributions, wake traverses at 5% and 40% axial chord downstream of the trailing edge and suction side boundary layer traverses were used to compare the performance of the three designs. The total pressure losses are strongly dependant on both the maximum velocity location as well as the diffusion on the suction surface. The importance of the behavior of the pressure surface boundary layer turned out to be negligible in comparison. Cases with equivalent operating Reynolds number and suction side diffusion level are compared in terms of the total pressure losses that are generated. It is shown that a relationship between loss and suction side maximum velocity location exists. An optimum suction side maximum velocity location depends on the Reynolds number, diffusion factor, and wake passing frequency.

scholarly journals Low-rise structures in reinforced concrete: approximation of material nonlinearity for global stability analysis

2018 ◽  
Vol 11 (1) ◽  
pp. 1-25
Author(s):  
L. M. MOREIRA ◽  
C. H. MARTINS
Keyword(s):  
Global Stability ◽  
Iterative Process ◽  
Global Analysis ◽  
Second Order ◽  
Material Nonlinearity ◽  
Flexural Stiffness ◽  
Analysis Model ◽  
Structural Element ◽  
Global Stability Analysis ◽  
Stiffness Reduction

Abstract In the analysis of the second-order global effects, the material nonlinearity (NLF) can be considered in an approximate way, defining for the set of each structural element a mean flexural stiffness. However, there is less research concerning low-rise buildings in the analysis of global stability in contrast to high buildings, because these have a greater sensitivity to this phenomenon and they are more studied. In this way, the paper objective is to determine the flexural stiffness values, of beams and columns, for buildings with less than four floors, to approximate consideration of the NLF in the global analysis. The idealized examples to buildings with 1, 2 and 3 floors, being simulated through the software CAD/TQS and an analysis model based in an iterative process. The simulations results defined the stiffness values of the set of beams and columns in each example, followed by a statistical analysis to define general values of application in the buildings. Finally, a proposal is suggested of stiffness reduction coefficients for beams and columns to be adopted in the approximation the NLF (EIsec = αv/p ∙ Eci Ic), as follows: buildings with 1 floor (αv = 0,17 and αp = 0,66), buildings with 2 floors (αv = 0,15 and αv = 0,71) and buildings with 3 floors (αv = 0,14 and αv = 0,72). The results obtained can be used for the analysis of low-rise structures to consider the second order global effects with more safely.

scholarly journals Control of the Unsteady Flow in a Stator Blade Row Interacting With Upstream Moving Wakes

1993 ◽  
Author(s):  
T. Valkov ◽  
C. S. Tan
Keyword(s):  
Unsteady Flow ◽  
Pressure Fluctuations ◽  
Spectral Element ◽  
Navier Stokes ◽  
Suction Surface ◽  
Model Calculations ◽  
Blade Loading ◽  
Pressure Surface ◽  
Blade Row ◽  
Stator Blade

A computational approach, based on a spectral-element Navier-Stokes solver, has been applied to the study of the unsteady flow arising from wake-stator interaction. Direct, as well as turbulence-model calculations, provide insight into the mechanics of the unsteady flow and demonstrate the potential for controlling its effects. The results show that the interaction between the wakes and the stator blades produces a characteristic pattern of vortical disturbances, which have been correlated to the pressure fluctuations. Within the stator passage, the wakes migrate towards the pressure surface where they evolve into counter-rotating vortices. These vortices are the dominant source of disturbances over the pressure surface of the stator blade. Over the suction surface of the stator blade, the disturbances are due to the distortion and detachment of boundary layer fluid. They can be reduced by tailoring the blade loading or by applying non-uniform suction.

Boundary Layer Development in the BR710 and BR715 LP Turbines—The Implementation of High-Lift and Ultra-High-Lift Concepts

2002 ◽  
Vol 124 (3) ◽  
pp. 385-392 ◽  
Author(s):  
R. J. Howell ◽  
H. P. Hodson ◽  
V. Schulte ◽  
R. D. Stieger ◽  
Heinz-Peter Schiffer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Test Facility ◽  
Surface Boundary ◽  
Unsteady Boundary Layer ◽  
Suction Surface ◽  
High Lift ◽  
Surface Boundary Layer ◽  
Cold Flow ◽  
Layer Behavior ◽  
Lp Turbine

This paper describes a detailed study into the unsteady boundary layer behavior in two high-lift and one ultra-high-lift Rolls-Royce Deutschland LP turbines. The objectives of the paper are to show that high-lift and ultra-high-lift concepts have been successfully incorporated into the design of these new LP turbine profiles. Measurements from surface mounted hot film sensors were made in full size, cold flow test rigs at the altitude test facility at Stuttgart University. The LP turbine blade profiles are thought to be state of the art in terms of their lift and design philosophy. The two high-lift profiles represent slightly different styles of velocity distribution. The first high-lift profile comes from a two-stage LP turbine (the BR710 cold-flow, high-lift demonstrator rig). The second high-lift profile tested is from a three-stage machine (the BR715 LPT rig). The ultra-high-lift profile measurements come from a redesign of the BR715 LP turbine: this is designated the BR715UHL LP turbine. This ultra-high-lift profile represents a 12 percent reduction in blade numbers compared to the original BR715 turbine. The results from NGV2 on all of the turbines show “classical” unsteady boundary layer behavior. The measurements from NGV3 (of both the BR715 and BR715UHL turbines) are more complicated, but can still be broken down into classical regions of wake-induced transition, natural transition and calming. The wakes from both upstream rotors and NGVs interact in a complicated manner, affecting the suction surface boundary layer of NGV3. This has important implications for the prediction of the flows on blade rows in multistage environments.

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