Spectral analysis and coherence of aerodynamic lift on rectangular cylinders in turbulent flow

2017 ◽  
Vol 830 ◽  
pp. 408-438 ◽  
Author(s):  
Shaopeng Li ◽  
Mingshui Li
Keyword(s):  
Turbulent Flow ◽  
Closed Form ◽  
Vertical Velocity ◽  
Lift Force ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Velocity Fluctuations ◽  
Dimensional Effects ◽  
Decay Parameters ◽  
Rectangular Cylinders

The goal of the present work is to derive the closed-form expressions of coherence and admittances to describe the spatial distribution of lift on rectangular cylinders in turbulent flow, which can be used to investigate the three-dimensional effects of turbulence. The coherence of the three-dimensional aerodynamic admittance (3D AAF), which takes into full account the spanwise variations in the vertical velocity fluctuations, is introduced to assess the validity of the strip assumption. A theoretical coherence model expressed in a double-exponential form is derived starting from the two-wavenumber spectral tensor of the lift on a thin aerofoil in Fourier space, providing us with explicit insight into the coherence of the lift force. Notably, it is an intrinsic property that the lift force on the structure is more strongly correlated than the oncoming flow and 3D AAF. This coherence model is extended to rectangular cylinders by the introduction of three floating parameters into the decay parameters of the 3D AAF. Based on theoretical and experimental investigations, it is shown that the three-dimensional effects of turbulence grow more prominent as the difference between the decay parameters of the 3D AAF and vertical velocity fluctuations decreases. A generalized approach for rapidly deriving the closed-form expressions of the admittances is proposed to study the unsteady behaviour of the lift force and the distortion of the free stream passing through the rectangular cylinders.

scholarly journals Experimental Investigations of Three-Dimensional Effects on Cavitating Hydrofoils

1961 ◽  
Vol 5 (03) ◽  
pp. 22-43
Author(s):  
R. W. Kermeen
Keyword(s):  
Aspect Ratio ◽  
High Speed ◽  
Three Dimensional ◽  
Cavitating Flow ◽  
Experimental Investigations ◽  
Water Tunnel ◽  
Pitching Moment ◽  
Two Dimensional ◽  
Dimensional Effects ◽  
Aspect Ratios

An investigation in the high-speed water tunnel of the hydsrodynamic characteristics of a family of three-dimensional sharp-edged hydrofoils is described. Four rectangular plan-form, 6-deg wedge profiles with aspect ratios of 4.0, 2.0, 1.0 and 0.5 were tested over a range of cavitation numbers from noncavitating to fully cavitating flow. The effects of aspect ratio on the flow and cavity configurations and on the lift, drag and pitching moment are discussed. Where data were available the results have been compared with the two-dimensional case.

Three-dimensional effects on the transfer function of a rectangular-section body in turbulent flow

2019 ◽  
Vol 872 ◽  
pp. 348-366 ◽  
Author(s):  
Yang Yang ◽  
Mingshui Li ◽  
Haili Liao
Keyword(s):  
Transfer Function ◽  
Turbulent Flow ◽  
Transfer Functions ◽  
Coherence Function ◽  
Three Dimensional ◽  
Accurate Estimation ◽  
Rectangular Section ◽  
Dimensional Effects ◽  
Aspect Ratios ◽  
Strip Theory

This paper investigates the influence of three-dimensional effects on the transfer function of a rectangular-section body in turbulent flow. The dimensionless factor $\unicode[STIX]{x1D713}$, as derived by Li et al. (J. Fluid Mech., vol. 847, 2018, pp. 768–785), is adapted to evaluate this influence. The calculation of $\unicode[STIX]{x1D713}$ requires the spanwise influence term. For this purpose, an adapted form of the lift coherence function is derived, enabling the use of the measured lift coherence for the estimation of the spanwise influence term. Three rectangular models with different cross-sections (chord-to-depth ratios of 3, 5 and 10) are chosen for testing, and a NACA 0015 airfoil model is tested for comparison. Using the measured spanwise influence terms, the dimensionless factors of these models are then numerically calculated under different ratios of the turbulent integral scale to the chord $\unicode[STIX]{x1D6FE}$ and aspect ratios $\unicode[STIX]{x1D703}$. It is shown that the dimensionless factors of the rectangular models increase as $\unicode[STIX]{x1D6FE}$ and $\unicode[STIX]{x1D703}$ increase, which are similar to the dimensionless factor of the airfoil model. If $\unicode[STIX]{x1D6FE}$ and $\unicode[STIX]{x1D703}$ have suitable values, the strip theory could be applicable to the rectangular-section body. It is also found that the dimensionless factors of all the rectangular models are larger than the dimensionless factor of the airfoil model under the same parameters. The smaller the chord-to-depth ratio is, the larger the dimensionless factor is. Using the strip theory to calculate the lift response of the rectangular-section body may provide more accurate estimation. Additionally, the one-wavenumber transfer functions of these models are determined under the consideration of the three-dimensional effects. The results show that the experimental transfer functions of the rectangular models cannot be captured by the Sears function. They are larger than the Sears function at lower frequencies, while falling at a faster rate as the frequency increases. For bluff bodies with separated flow, the modified transfer function presented here appears to be an appropriate approach.

Experimental investigations of three-dimensional effects near a crack tip using computer vision

1992 ◽  
Vol 53 (3) ◽  
pp. 201-228
Author(s):  
M. A. Sutton ◽  
J. L. Turner ◽  
Y. J. Chao ◽  
H. A. Bruck ◽  
T. L. Chae
Keyword(s):  
Computer Vision ◽  
Three Dimensional ◽  
Crack Tip ◽  
Experimental Investigations ◽  
Dimensional Effects

Development of Fixed Hydrodynamic Lifting Surfaces to Stabilise Anchoring Structures in Energetic Tidal Flows

2012 ◽  
Author(s):  
Samuel F. Harding ◽  
Ian G. Bryden
Keyword(s):  
Vertical Velocity ◽  
Lift Force ◽  
Longitudinal Velocity ◽  
Combined Effect ◽  
Potential Contribution ◽  
Velocity Fluctuations ◽  
Unsteady Aerodynamic ◽  
Tidal Flows ◽  
Lifting Surfaces ◽  
Set Up

This paper presents the research currently being carried out on the potential contribution of hydrofoils to generate additional down-force on seabed fastenings in energetic tidal flows. Firstly, the dynamic lift of a hydrofoil subjected to vertical velocity perturbations was analyzed numerically, showing the reduced response to the fluctuation when unsteady aerodynamic theories are introduced. Secondly, an experimental set-up was developed for the deterministic generation of two-dimension velocity perturbations in a recirculating water flume. This will allow the combined effect of vertical and longitudinal velocity fluctuations on the lift force to be measured.

Sign in / Sign up

Export Citation Format

Share Document