Anisotropy of small-scale scalar turbulence

2001 ◽  
Vol 448 ◽  
pp. 279-288 ◽  
Author(s):  
SUSAN KURIEN ◽  
KONSTANTINOS G. AIVALIS ◽  
KATEPALLI R. SREENIVASAN
Keyword(s):  
Reynolds Number ◽  
Spherical Harmonics ◽  
High Reynolds Number ◽  
Temperature Fluctuations ◽  
Small Scale ◽  
Surface Layers ◽  
Isotropic Part ◽  
Scalar Turbulence ◽  
Scale Temperature ◽  
High Reynolds

The anisotropy of small-scale temperature fluctuations in shear flows is analysed by making measurements in high-Reynolds-number atmospheric surface layers. A spherical harmonics representation of the moments of scalar increments is proposed, such that the isotropic part corresponds to the index j = 0 and increasing degrees of anisotropy correspond to increasing j. The parity and angular dependence of the odd moments of the scalar increments show that the moments cannot contain any isotropic part (j = 0), but can be satisfactorily represented by the lowest-order anisotropic term corresponding to j = 1. Thus, the skewnesses of scalar increments (and derivatives) are inherently anisotropic quantities, and are not suitable indicators of the tendency towards isotropy.

Models of the scalar spectrum for turbulent advection

1978 ◽  
Vol 88 (3) ◽  
pp. 541-562 ◽  
Author(s):  
R. J. Hill
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Schmidt Number ◽  
Temperature Fluctuations ◽  
Limited Extent ◽  
Temperature Spectrum ◽  
One Dimensional ◽  
Moderate Reynolds Number ◽  
Temperature Spectra ◽  
High Reynolds

Several models are developed for the high-wavenumber portion of the spectral transfer function of scalar quantities advected by high-Reynolds-number, locally isotropic turbulent flow. These models are applicable for arbitrary Prandtl or Schmidt number, v/D, and the resultant scalar spectra are compared with several experiments having different v/D. The ‘bump’ in the temperature spectrum of air observed over land is shown to be due to a tendency toward a viscous-convective range and the presence of this bump is consistent with experiments for large v/D. The wavenumbers defining the transition between the inertial-convective range and viscous-convective range for asymptotically large v/D (denoted k* and k1* for the three- and one-dimensional spectra) are determined by comparison of the models with experiments. A measurement of the transitional wavenumber k1* [denoted (k1*)s] is found to depend on v/D and on any filter cut-off. On the basis of the k* values it is shown that measurements of β1 from temperature spectra in moderate Reynolds number turbulence in air (v/D = 0·72) maybe over-estimates and that the inertial-diffusive range of temperature fluctuations in mercury (v/D ≃ 0·02) is of very limited extent.

Validation case for supersonic boundary layer and turbulent aero-optical investigation in high-Reynolds-number freestream by WCNS-E-5

2020 ◽  
Vol 234 (15) ◽  
pp. 2153-2166 ◽  
Author(s):  
Xi-Wan Sun ◽  
Wei Liu
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
High Reynolds Number ◽  
Numerical Technique ◽  
Small Scale ◽  
Spanwise Direction ◽  
Optical Investigation ◽  
Computational Domain ◽  
Velocity Correlation ◽  
High Reynolds

Turbulent flat-plate boundary layer flows have been widely employed for numerical validation in the aero-optical field. In present study, the laminar-to-turbulent evolution induced by wavy roughness in high-Reynolds-number supersonic freestream is investigated using a numerical technique based on the fifth-order weighted compact nonlinear scheme (WCNS-E-5). The computational procedure and post-processing method are described in detail, and the acquired instantaneous flow structure and statistical data are compared with other theoretical, experimental, and numerical results to demonstrate the feasibility of predicting turbulence using WCNS-E-5. Further, to reduce the computational resources required to simulate turbulent flow, a velocity correlation function is introduced to decrease the computational domain in the spanwise direction. Additionally, the effects of different grid sizes on the simulation results are examined by reducing the number of cells in the streamwise, wall-normal, and spanwise directions. Finally, the authors conduct a tentative investigation into the aero-optical effects of the laminar-to-turbulent flowfield using a ray-tracing method, considering both the feasibility of aero-optical detection and the effect of grid scale on the time-averaged imaging quality, as well as a deeper probe into the characteristic structures reflected by aero-optical frequency spectrum. The results elucidated that the wall-normal grid number has the strongest influence on the transitional location, and undoubtedly affects wavefront aberrations. However, different gird scales lead to similar aero-optical spectrum, and revealed the Kolmogorov-type turbulence at small-scale regime. As a prelude to further aero-optical simulations of wall-bounded flows, the current study provides some reference for the code validation process and aero-optical interrogation.

Small-Scale Dynamics of High-Reynolds-Number Two-Dimensional Turbulence

1986 ◽  
Vol 57 (6) ◽  
pp. 683-686 ◽  
Author(s):  
M. E. Brachet ◽  
M. Meneguzzi ◽  
P. L. Sulem
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Small Scale ◽  
Two Dimensional ◽  
High Reynolds

scholarly journals A CFD Simulation on the Performance of Slotted Propeller Design for Various Airfoil Configurations

CFD letters ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 43-57
Author(s):  
Wan Mazlina Wan Mohamed ◽  
Nirresh Prabu Ravindran ◽  
Parvathy Rajendran
Keyword(s):  
Reynolds Number ◽  
Power Efficiency ◽  
High Reynolds Number ◽  
Power Coefficient ◽  
Small Scale ◽  
Power Ratio ◽  
Thrust Coefficient ◽  
High Lift ◽  
Propeller Design ◽  
High Reynolds

The usage of slots has gained renewed interest in aerospace, particularly on propeller design. Most of the works have focused on improving the aerodynamic performance and efficiency. Modern research on propeller design aims to design propellers with high thrust performance under low torque conditions without any weight penalty. Although research on slotted design has been done before, none has been done to understand its impact on different airfoils on the propeller blade. Thus, this study aims to provide extensive research on slotted propeller design with various airfoil of different properties such as high Reynolds number, low Reynolds number, symmetrical, asymmetrical high lift, and low drag. This work has been investigated using computational fluid dynamics method to predict propeller performance for a small-scale propeller. The slotted blade designs' performance is presented in terms of thrust coefficient, power coefficient, efficiency, and thrust to power ratio. Here, the slotted APC Slow Flyer propeller blade's performance has been investigated for diverse types of airfoils with the shape and position of the slot is fixed which is a square-shaped at 62.5% of the chord length. The flow simulations are performed through three-dimensional computational fluid dynamic software (ANSYS Fluent) to determine the thrust coefficient, power coefficient, efficiency, and thrust to power ratio measured in advancing flow conditions. Findings show that the slotted propeller design composed of symmetrical, high Reynolds number, high lift airfoils can benefit the most with slots' implementation. These improvements were 19.49%, 69.13%, 53.57% and 111.06% in terms of thrust, power, efficiency and trust to power ratio respectively.

scholarly journals Fractal iso-level sets in high-Reynolds-number scalar turbulence

2020 ◽  
Vol 5 (4) ◽  
Author(s):  
Kartik P. Iyer ◽  
Jörg Schumacher ◽  
Katepalli R. Sreenivasan ◽  
P. K. Yeung
Keyword(s):  
Reynolds Number ◽  
Level Sets ◽  
High Reynolds Number ◽  
Scalar Turbulence ◽  
High Reynolds

scholarly journals Phase relations in a forced turbulent boundary layer: implications for modelling of high Reynolds number wall turbulence

2017 ◽  
Vol 375 (2089) ◽  
pp. 20160080 ◽  
Author(s):  
Subrahmanyam Duvvuri ◽  
Beverley McKeon
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
High Reynolds Number ◽  
Phase Relations ◽  
Wall Turbulence ◽  
Large Reynolds Number ◽  
Small Scale ◽  
Scale Interactions ◽  
High Reynolds

Phase relations between specific scales in a turbulent boundary layer are studied here by highlighting the associated nonlinear scale interactions in the flow. This is achieved through an experimental technique that allows for targeted forcing of the flow through the use of a dynamic wall perturbation. Two distinct large-scale modes with well-defined spatial and temporal wavenumbers were simultaneously forced in the boundary layer, and the resulting nonlinear response from their direct interactions was isolated from the turbulence signal for the study. This approach advances the traditional studies of large- and small-scale interactions in wall turbulence by focusing on the direct interactions between scales with triadic wavenumber consistency. The results are discussed in the context of modelling high Reynolds number wall turbulence. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’.

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