New Theories on Boundary Layer Transition and Turbulence Formation

Liu, Chaoqun; Lü, Ping; Chen, Lin; Yan, Ya

doi:10.1155/2012/619419

Cited by 7 publications

(2 citation statements)

References 34 publications

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“…The Navier-Stokes relations are originally based on the continuum hypothesis [3] and assuming the flow processes to be governed by Newton's viscosity law (a nearequilibrium irreversible thermodynamic process) [15]. This set of relations can be excellently applied on laminar flows, however, this set of relations is also assumed to be valid in turbulent flows [15][16][17][18][19][20][21]. Commonly, in CTT, a Reynolds decomposition is made, allowing for a simplification of the Navier-Stokes relations.…”

Section: Introductionmentioning

confidence: 99%

Novel Approach for Turbulent Flow- and Onset Analysis

K. Gustavsson

2024

Boundary Layer Flows - Advances in Experimentation, Modelling and Simulation

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It is a well-known fact that the matching of experimental data to turbulence models have hitherto not been successful. An example of this is the inability to theoretically predict the Re number at which turbulence onset (transition) occurs. In this paper, some advantages of adopting a “far-from-equilibrium” irreversible process analysis are demonstrated: To illustrate, one may at a single geometric point near a solid wall, compute conditions for mass conservation, 1st, and 2nd laws of thermodynamics – assuming either Newton’s viscosity law- or an alternative far-from-equilibrium fundamental model to be valid. While these conditions generally differ for various flows, it is observed that these conditions numerically match each other at ReD around 2300 for a fully developed pipe flow, or at Rex between 5 × 105 to 3 × 106 in a developing flat-plate boundary layer flow. This suggests that turbulence onset can be correctly predicted using the novel approach. Criteria and recommendations for experimental flow measurements, i.e. testing conditions, within a proposed far-from-equilibrium zone (e.g. viscous sublayer) is discussed as well.

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Section: Introductionmentioning

confidence: 99%

Novel Approach for Turbulent Flow- and Onset Analysis

K. Gustavsson

2024

Boundary Layer Flows - Advances in Experimentation, Modelling and Simulation

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“…After a cascade breakdown of eddies, eventually to the smallest scales (the Kolmogorov scales [9]), any further breakdown is the conversion into viscous dissipation.  Perhaps the most ambitious computational-intense approach is the DNS (Direct Numerical Simulation) approach [7], [10], computing the time-dependent solutions of the flow utilizing the unaltered Navier-Stokes relations. Unfortunately, when modelling a situation where turbulence has triggered and is growing downstream (e.g.…”

Section: Introductionmentioning

confidence: 99%

A Residual Thermodynamic Analysis of Turbulence – Part 1: Theory

Gustavsson¹

2022

International Journal of Thermodynamics

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A new theoretical groundwork for the analysis of wall-bounded turbulent flows is offered, the application of which is presented in a parallel paper. First, it is proposed that the turbulence phenomenon is connected to the onset of an irreversible process – specifically the action of a slip flow – by which a new fundamental model can be derived. Fluid cells with specific dimensions – of length connected with the local slip length and thickness connected with the distance between two parallel slipping flows – can be hypothetically constructed, in which a specific kinetic energy dissipation can be considered to occur. Second, via a maximum entropy production process a self-organized grouping of cells occurs – which results in the distinct zones viscous sublayer, buffer layer, and the log-law region to be built up. It appears that the underlying web structure may take the form of either representing a perfect web structure without any visible swirls, or a partially defect web structure where unbalanced forces may result in the generation of apparent swirls – which in turn might grow into larger turbulent eddies. Third, on the transition from laminar to turbulent flows, a nominal connection between the onset of a turbulent wall boundary layer (in a pipe flow), the Reynolds number as well as the wall surface roughness can be derived.

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The effect of leading-edge shape on separation-induced transition on the suction surface of a controlled-diffusion airfoil

2023

Physics of Fluids

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To investigate the effect of leading-edge shape on separation-induced transition on suction surface, a large eddy simulation is performed on two compressor controlled-diffusion airfoils: a conventional one with an elliptical leading edge and an optimized one with a curvature-continuous design based on the B-spline description. The Reynolds number based on inflow velocity and chord length is 4.5×105. The critical angle of attack +4°, over which the aerodynamic loss rises sharply, is chosen for simulation. Two transitions are observed on the suction surface, one near the leading edge and the other at 40% chord length. The primary difference between the two airfoils lies in the leading-edge transition, which also leads to the distinction of fluctuating velocity amplitude and energy loss in the subsequent development of boundary layer flow. In order to provide an insight into the transition mechanism, the frequency spectrum analysis is conducted, and the results indicate that the amplification of disturbances during transition is dominated by Kelvin–Helmholtz instability. The mechanisms of energy transport and dissipation are analyzed, and the influence of leading-edge curvature on the initial state of boundary layer flow is elucidated from a dynamic perspective. The results show that continuous and large curvature distributions are more conducive to suppressing the formation of leading-edge separation bubble and delaying the onset of transition.

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New Theories on Boundary Layer Transition and Turbulence Formation

Cited by 7 publications

References 34 publications

Novel Approach for Turbulent Flow- and Onset Analysis

Novel Approach for Turbulent Flow- and Onset Analysis

A Residual Thermodynamic Analysis of Turbulence – Part 1: Theory

The effect of leading-edge shape on separation-induced transition on the suction surface of a controlled-diffusion airfoil

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