scholarly journals Hyperbolicity, shadowing directions and sensitivity analysis of a turbulent three-dimensional flow

2019 ◽  
Vol 863 ◽  
pp. 644-669 ◽  
Author(s):  
Angxiu Ni
Keyword(s):  
Reynolds Number ◽  
Large Fraction ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Wake Region ◽  
Near Wake ◽  
Three Dimensional Flow ◽  
Long Time ◽  
Cylinder Flow ◽  
Far Wake

This paper uses compressible flow simulation to analyse the hyperbolicity, shadowing directions and sensitivities of a weakly turbulent three-dimensional cylinder flow at Reynolds number 525 and Mach number 0.1. By computing the first 40 covariant Lyapunov vectors (CLVs), we find that unstable CLVs are active in the near-wake region, whereas stable CLVs are active in the far-wake region. This phenomenon is related to hyperbolicity since it shows that CLVs point to different directions; it also suggests that for open flows there is a large fraction of CLVs that are stable. However, due to the extra neutral CLV and the occasional tangencies between CLVs, our system is not uniform hyperbolic. By the non-intrusive least-squares shadowing (NILSS) algorithm, we compute shadowing directions and sensitivities of long-time-averaged objectives. Our results suggest that shadowing methods may be valid for general chaotic fluid problems.

scholarly journals Modification of three-dimensional transition in the wake of a rotationally oscillating cylinder

2009 ◽  
Vol 643 ◽  
pp. 349-362 ◽  
Author(s):  
DAVID LO JACONO ◽  
JUSTIN S. LEONTINI ◽  
MARK C. THOMPSON ◽  
JOHN SHERIDAN
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Oscillation Mode ◽  
Critical Amplitude ◽  
Near Wake ◽  
Three Dimensional Flow ◽  
Double Row ◽  
Dimensional Flow ◽  
Spatio Temporal ◽  
Mode A

A study of the flow past an oscillatory rotating cylinder has been conducted, where the frequency of oscillation has been matched to the natural frequency of the vortex street generated in the wake of a stationary cylinder, at Reynolds number 300. The focus is on the wake transition to three-dimensional flow and, in particular, the changes induced in this transition by the addition of the oscillatory rotation. Using Floquet stability analysis, it is found that the fine-scale three-dimensional mode that typically dominates the wake at a Reynolds number beyond that at the second transition to three-dimensional flow (referred to as mode B) is suppressed for amplitudes of rotation beyond a critical amplitude, in agreement with past studies. However, the rotation does not suppress the development of three-dimensionality completely, as other modes are discovered that would lead to three-dimensional flow. In particular, the longer-wavelength mode that leads the three-dimensional transition in the wake of a stationary cylinder (referred to as mode A) is left essentially unaffected at low amplitudes of rotation. At higher amplitudes of oscillation, mode A is also suppressed as the two-dimensional near wake changes in character from a single- to a double-row wake; however, another mode is predicted to render the flow three-dimensional, dubbed mode D (for double row). This mode has the same spatio-temporal symmetries as mode A.

scholarly journals Two-scale dynamics of flow past a partial cross-stream array of tidal turbines

2013 ◽  
Vol 730 ◽  
pp. 220-244 ◽  
Author(s):  
Takafumi Nishino ◽  
Richard H. J. Willden
Keyword(s):  
Analytical Model ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Wake Region ◽  
Near Wake ◽  
New Model ◽  
Tidal Turbines ◽  
Type Design ◽  
Flow Past ◽  
Far Wake

AbstractThe characteristics of flow past a partial cross-stream array of (idealized) tidal turbines are investigated both analytically and computationally to understand the mechanisms that determine the limiting performance of partial tidal fences. A two-scale analytical partial tidal fence model reported earlier is further extended by better accounting for the effect of array-scale flow expansion on device-scale dynamics, so that the new model is applicable to short fences (consisting of a small number of devices) as well as to long fences. The new model explains theoretically general trends of the limiting performance of partial tidal fences. The new model is then compared to three-dimensional Reynolds-averaged Navier–Stokes (RANS) computations of flow past an array of various numbers (up to 40) of actuator disks. On the whole, the analytical model agrees well with the RANS computations, suggesting that the two-scale dynamics described in the analytical model predominantly determines the fence performance in the RANS computations as well. The comparison also suggests that the limiting performance of short partial fences depends on how much of device far-wake mixing takes place within the array near-wake region. This factor, however, depends on the structures of the wake and therefore on the type/design of devices to be arrayed.

Three-dimensional flow over two spheres placed side by side

1993 ◽  
Vol 246 ◽  
pp. 465-488 ◽  
Author(s):  
Inchul Kim ◽  
Said Elghobashi ◽  
William A. Sirignano
Keyword(s):  
Reynolds Number ◽  
Vortical Structure ◽  
Three Dimensional ◽  
Numerical Data ◽  
Reynolds Numbers ◽  
Near Wake ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Confined Flow ◽  
Small Spacing

Three-dimensional flow over two identical (solid or liquid) spheres which are held fixed relative to each other with the line connecting their centres normal to a uniform I stream is investigated numerically at Reynolds numbers 50, 100, and 150. We consider the lift, moment, and drag coefficients on the spheres and investigate their dependence on the distance between the two spheres. The computations show that, for a given Reynolds number, the two spheres are repelled when the spacing is of the order of the diameter but are weakly attracted at intermediate separation distances. For small spacing, the vortical structure of the near wake is significantly different from that of the axisymmetric wake that establishes at large separations. The partially confined flow passing between the two spheres entrains the flows coming around their other sides. Our results agree with available experimental and numerical data.

scholarly journals Measurements of Secondary Flows Within a Cascade of Curved Blades and in the Wake of the Cascade

1983 ◽  
Author(s):  
Ronald Lasser ◽  
Wilfred T. Rouleau
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Three Dimensional ◽  
Laser Doppler Anemometer ◽  
Secondary Flows ◽  
Wake Region ◽  
Near Wake ◽  
Primary Flow ◽  
Turning Angle ◽  
Blade Cascade

A laser-Doppler anemometer was used to measure the three-dimensional velocity field within a typical turbine blade cascade. The blades had a 12.7 cm chord, a turning angle of 104.8°, and a shape conforming to the camber line of a commercial turboexpander. The cascade was operated at a Reynolds number of 1.25×105. Strong secondary velocities, ranging up to 35 percent of the primary flow velocity, were found, resulting from the development of counter-rotating vortices within the blade passages. Large midspan velocity defects in the primary flow were coincident with these high secondary flows. The secondary flow persisted throughout the near wake region.

Numerical Study of Flow Past a Solid Sphere at Moderate Reynolds Number

2014 ◽  
Vol 660 ◽  
pp. 674-678 ◽  
Author(s):  
Azmahani Sadikin ◽  
Nurul Akma Mohd Yunus ◽  
Kamil Abdullah ◽  
Akmal Nizam Mohammed
Keyword(s):  
Reynolds Number ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Solid Sphere ◽  
Three Dimensional Flow ◽  
Numerical Investigations ◽  
Moderate Reynolds Number ◽  
High Reynolds

The unsteady three dimensional flow simulation around sphere using numerical simulation computational fluid dynamic for moderate Reynolds Number between 20 ≤ Re ≤ 500 is presented. The aim of this work is to analyze the flow regimes around sphere and flow separation. Extensive comparisons were made between the present predicted results and available experimental and numerical investigations, and showed that they are in close agreement. The results show that the vortex shedding increases with the Reynolds number. The flow separates early when Reynolds number increases, therefore the separation angle is found to be smaller when high Reynolds number is present.

Three-Dimensional Flow Simulation Research on Spur Dike

2013 ◽  
Vol 405-408 ◽  
pp. 799-802
Author(s):  
Hui Xu ◽  
Ming Zhang ◽  
Wan Qi Zhang
Keyword(s):  
Three Dimensional ◽  
Vertical Plane ◽  
Flow Simulation ◽  
Free Water ◽  
Three Dimensional Flow ◽  
Simulation Research ◽  
Spur Dike ◽  
Additional Layer ◽  
Large Coefficient ◽  
Coefficient Method

A three-dimensional (3D) flow mathematical model has been applied to simulate the flow field around spur dikes. In the vertical plane, the z-coordinate was adopted, and the additional layer was used to track the free water surface. The standard k-ε model was adopted, additionally, wall function and large coefficient method was applied to treat the boundary of the spur dike. Simulated results of velocity distribution, turbulent kinetic energy and its dissipation rate around the spur dike agree well with the experimental data.

Three dimensional flow simulation over a sharp-crested V-Notch weir

2020 ◽  
Vol 71 ◽  
pp. 101684 ◽  
Author(s):  
Hamid Saadatnejadgharahassanlou ◽  
Rasoul Ilkhanipour Zeynali ◽  
Amin Gharehbaghi ◽  
Saeid Mehdizadeh ◽  
Babak Vaheddoost
Keyword(s):  
Three Dimensional ◽  
Flow Simulation ◽  
Three Dimensional Flow ◽  
Dimensional Flow
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