Boundary layer turbulence and freestream turbulence interface, turbulent spot and freestream turbulence interface, laminar boundary layer and freestream turbulence interface

Abstract High Reynolds flow over a nozzle guide-vane with elevated inflow turbulence was simulated using wall-resolved large eddy simulation (LES). The simulations were undertaken at an exit Reynolds number of 0.5 × 106 and inflow turbulence levels of 0.7% and 7.9% and for uniform heat-flux boundary conditions corresponding to the measurements of Varty and Ames (2016, “Experimental Heat Transfer Distributions Over an Aft Loaded Vane With a Large Leading Edge at Very High Turbulence Levels,” ASME Paper No. IMECE2016-67029). The predicted heat transfer distribution over the vane is in excellent agreement with measurements. At higher freestream turbulence, the simulations accurately capture the laminar heat transfer augmentation on the pressure surface and the transition to turbulence on the suction surface. The bypass transition on the suction surface is preceded by boundary layer streaks formed under the external forcing of freestream disturbances which breakdown to turbulence through inner-mode secondary instabilities. Underneath the locally formed turbulent spot, heat transfer coefficient spikes and generally follows the same pattern as the turbulent spot. The details of the flow and temperature fields on the suction side are characterized, and first- and second-order statistics are documented. The turbulent Prandtl number in the boundary layer is generally in the range of 0.7–1, but decays rapidly near the wall.

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Experimental study of disturbances produced in a pre-transitional laminar boundary layer by weak freestream turbulence

10.2514/6.1985-1695 ◽

1985 ◽

Cited By ~ 56

Author(s):

J. KENDALL

Keyword(s):

Boundary Layer ◽

Experimental Study ◽

Laminar Boundary Layer ◽

Freestream Turbulence

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Boundary-Layer Transition in Accelerating Flows With Intense Freestream Turbulence: Part 2—The Zone of Intermittent Turbulence

Journal of Fluids Engineering ◽

10.1115/1.2910033 ◽

1992 ◽

Vol 114 (3) ◽

pp. 322-332 ◽

Cited By ~ 13

Author(s):

M. F. Blair

Keyword(s):

Boundary Layer ◽

Turbulent Boundary Layer ◽

Boundary Layer Transition ◽

Transitional Region ◽

Freestream Turbulence ◽

Intermittent Turbulence ◽

Adiabatic Wall ◽

Layer Transition ◽

Flow Acceleration ◽

Boundary Layer Turbulence

Hot-wire anemometry was employed to examine the laminar-to-turbulent transition of low-speed, two-dimensional boundary layers for two (moderate) levels of flow acceleration and various levels of grid-generated freestream turbulence. Flows with an adiabatic wall and with uniform-flux heat transfer were explored. Conditional discrimination techniques were employed to examine the zones of flow within the transitional region. This analysis demonstrated that as much as one-half of the streamwise-component unsteadiness, and much of the apparent anisotropy, observed near the wall was produced, not by turbulence, but by the steps in velocity between the turbulent and inter-turbulent zones of flow. Within the turbulent zones u′/v′ ratios were about equal to those expected for equilibrium boundary-layer turbulence. Near transition onset, however, the turbulence kinetic energy within the turbulent zones exceeded fully turbulent boundary-layer levels. Turbulent-zone power-spectral-density measurements indicate that the ratio of dissipation to production increased through transition. This suggests that the generation of the full equilibrium turbulent boundary-layer energy cascade required some time (distance) and may explain the very high TKE levels near onset.

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On the evolution of a wave packet in a laminar boundary layer

Journal of Fluid Mechanics ◽

10.1017/s0022112091002185 ◽

1991 ◽

Vol 225 ◽

pp. 575-606 ◽

Cited By ~ 51

Author(s):

Jacob Cohen ◽

Kenneth S. Breuer ◽

Joseph H. Haritonidis

Keyword(s):

Boundary Layer ◽

Wave Packet ◽

Linear Stability ◽

Laminar Boundary Layer ◽

Stability Theory ◽

Free Stream ◽

Linear Stability Theory ◽

Stream Velocity ◽

Turbulent Spot ◽

Second Stage

The transition process of a small-amplitude wave packet, generated by a controlled short-duration air pulse, to the formation of a turbulent spot is traced experimentally in a laminar boundary layer. The vertical and spanwise structures of the flow field are mapped at several downstream locations. The measurements, which include all three velocity components, show three stages of transition. In the first stage, the wave packet can be treated as a superposition of two- and three-dimensional waves according to linear stability theory, and most of the energy is centred around a mode corresponding to the most amplified wave. In the second stage, most of the energy is transferred to oblique waves which are centred around a wave having half the frequency of the most amplified linear mode. During this stage, the amplitude of the wave packet increases from 0.5 % to 5 % of the free-stream velocity. In the final stage, a turbulent spot develops and the amplitude of the disturbance increases to 27 % of the free-stream velocity.Theoretical aspects of the various stages are considered. The amplitude and phase distributions of various modes of all three velocity components are compared with the solutions provided by linear stability theory. The agreement between the theoretical and measured distributions is very good during the first two stages of transition. Based on linear stability theory, it is shown that the two-dimensional mode of the streamwise velocity component is not necessarily the most energetic wave. While linear stability theory fails to predict the generation of the oblique waves in the second stage of transition, it is demonstrated that this stage appears to be governed by Craik-type subharmonic resonances.

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Large Eddy Simulation of Bypass Transition in Vane Passage With Freestream Turbulence

Volume 5B: Heat Transfer ◽

10.1115/gt2019-91099 ◽

2019 ◽

Author(s):

Yousef Kanani ◽

Sumanta Acharya ◽

Forrest Ames

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Large Eddy Simulation ◽

Bypass Transition ◽

Freestream Turbulence ◽

Turbulent Spot ◽

Suction Surface ◽

Eddy Simulation ◽

Large Eddy ◽

Inflow Turbulence

Abstract High Reynolds flow over a nozzle guide-vane with elevated inflow turbulence was simulated using wall-resolved large eddy simulation (LES). The simulations were undertaken at an exit Reynolds number of 0.5×106 and inflow turbulence levels of 0.7% and 7.9% and for uniform heat-flux boundary conditions corresponding to the measurements of (Varty, J. W., and Ames, F. E., 2016, ASME Paper No. IMECE2016-67029). The predicted heat transfer distribution over the vane is in excellent agreement with measurements. At higher freestream turbulence, the simulations accurately capture the laminar heat transfer augmentation on the pressure surface and the transition to turbulence on the suction surface. The bypass transition on the suction surface is preceded by boundary layer streaks formed under the external forcing of freestream disturbances which breakdown to turbulence through inner mode secondary instabilities. Underneath the locally formed turbulent spot, heat transfer coefficient spikes and generally follows the same pattern as the turbulent spot. The details of the flow and temperature fields on the suction side are characterized and first and second order statistics are documented. The turbulent Prandtl number in the boundary layer is generally in the range of 0.7–1, but decays rapidly near the wall.

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An Investigation Using Wavelet Analysis Into Velocity Perturbations Under the Influence of Elevated Freestream Turbulence at Transition Onset

Volume 6: Turbomachinery, Parts A and B ◽

10.1115/gt2006-90987 ◽

2006 ◽

Cited By ~ 2

Author(s):

Domhnaill M. Hernon ◽

Edmond J. Walsh ◽

Donald M. McEligot

Keyword(s):

Boundary Layer ◽

Wavelet Analysis ◽

Transitional Flow ◽

Computational Techniques ◽

Wall Region ◽

Freestream Turbulence ◽

Turbulent Spot ◽

Perturbation Velocity ◽

Boundary Layer Edge ◽

Near Wall

The development of streamwise-orientated disturbances at transition onset for zero-pressure gradient boundary layer flow under the influence of 1.3% freestream turbulence intensity is presented. The analysis concentrates on the development of turbulent spots and other coherent structures with the use of wavelet analysis. The turbulent spot structure is shown to change dramatically in shape, sign of perturbation velocity and energy content from the near wall region to the boundary layer edge. An increased number of trubulent structures are observed near the boundary layer edge, all with negative perturbation velocities, compared to those of positive perturbation velocity in the near wall region. The wavelet maps demonstrate some interesting features of turbulent spot development including regions of high frequency disturbance growth prior to the spot passing the sensor. Distributions of peak negative, peak positive and averaged perturbation velocities were obtained at three streamwise positions prior to transition onset. As transition onset approached the magnitude of the negative value far exceeded the positive and their relative positions within the boundary layer changed considerably. The results presented in this report give further insight into the physics of pre-transitional flow illustrating the influence of negative perturbation velocity in the transition process. Furthermore, the importance of peak instantaneous perturbations compared to averaged values is also demonstrated, a feature of the flow that computational techniques will have to model in order to accurately predict transition phenomena.

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On a turbulent ‘spot’ in a laminar boundary layer

Journal of Fluid Mechanics ◽

10.1017/s0022112076002747 ◽

1976 ◽

Vol 78 (04) ◽

pp. 785 ◽

Cited By ~ 131

Author(s):

I. Wygnanski ◽

M. Sokolov ◽

D. Friedman

Keyword(s):

Boundary Layer ◽

Laminar Boundary Layer ◽

Turbulent Spot

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