Transition Phenomena on Airfoils Operating at Low Chord Reynolds Numbers in Steady and Unsteady Flow

1990 ◽  
pp. 333-344 ◽  
Author(s):  
M. Brendel ◽  
T. J. Mueller
Keyword(s):  
Unsteady Flow ◽  
Reynolds Numbers

scholarly journals The drag-adjoint field of a circular cylinder wake at Reynolds numbers 20, 100 and 500

2013 ◽  
Vol 730 ◽  
pp. 145-161 ◽  
Author(s):  
Qiqi Wang ◽  
Jun-Hui Gao
Keyword(s):  
Circular Cylinder ◽  
Flow Field ◽  
Unsteady Flow ◽  
Numerical Solutions ◽  
Reynolds Numbers ◽  
Adjoint Equations ◽  
Cylinder Wake ◽  
Near Wake ◽  
Navier Stokes Equation ◽  
D 20

AbstractThis paper analyses the adjoint solution of the Navier–Stokes equation. We focus on flow across a circular cylinder at three Reynolds numbers, ${\mathit{Re}}_{D} = 20, 100$ and $500$. The quantity of interest in the adjoint formulation is the drag on the cylinder. We use classical fluid mechanics approaches to analyse the adjoint solution, which is a vector field similar to a flow field. Production and dissipation of kinetic energy of the adjoint field is discussed. We also derive the evolution of circulation of the adjoint field along a closed material contour. These analytical results are used to explain three numerical solutions of the adjoint equations presented in this paper. The adjoint solution at ${\mathit{Re}}_{D} = 20$, a viscous steady state flow, exhibits a downstream suction and an upstream jet, the opposite of the expected behaviour of a flow field. The adjoint solution at ${\mathit{Re}}_{D} = 100$, a periodic two-dimensional unsteady flow, exhibits periodic, bean-shaped circulation in the near-wake region. The adjoint solution at ${\mathit{Re}}_{D} = 500$, a turbulent three-dimensional unsteady flow, has complex dynamics created by the shear layer in the near wake. The magnitude of the adjoint solution increases exponentially at the rate of the first Lyapunov exponent. These numerical results correlate well with the theoretical analysis presented in this paper.

Drag of a sphere in an unsteady flow of viscous fluid at small reynolds numbers

1988 ◽  
Vol 23 (1) ◽  
pp. 6-10 ◽  
Author(s):  
M. N. Gaidukov ◽  
V. G. Roman ◽  
Yu. I. Yalamov
Keyword(s):  
Viscous Fluid ◽  
Unsteady Flow ◽  
Reynolds Numbers ◽  
Small Reynolds Numbers

Unsteady flow about a sphere at low to moderate Reynolds number. Part 1. Oscillatory motion

1994 ◽  
Vol 277 ◽  
pp. 347-379 ◽  
Author(s):  
Eugene J. Chang ◽  
Martin R. Maxey
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Steady Flow ◽  
Oscillatory Flow ◽  
Reynolds Numbers ◽  
Oscillatory Motion ◽  
Rigid Sphere ◽  
Flow Conditions ◽  
Steady Streaming ◽  
Moderate Reynolds Number

A direct numerical simulation, based on spectral methods, has been used to compute the time-dependent, axisymmetric viscous flow past a rigid sphere. An investigation has been made for oscillatory flow about a zero mean for different Reynolds numbers and frequencies. The simulation has been verified for steady flow conditions, and for unsteady flow there is excellent agreement with Stokes flow theory at very low Reynolds numbers. At moderate Reynolds numbers, around 20, there is good general agreement with available experimental data for oscillatory motion. Under steady flow conditions no separation occurs at Reynolds number below 20; however in an oscillatory flow a separation bubble forms on the decelerating portion of each cycle at Reynolds numbers well below this. As the flow accelerates again the bubble detaches and decays, while the formation of a new bubble is inhibited till the flow again decelerates. Steady streaming, observed for high frequencies, is also observed at low frequencies due to the flow separation. The contribution of the pressure to the resultant force on the sphere includes a component that is well described by the usual added-mass term even when there is separation. In a companion paper the flow characteristics for constant acceleration or deceleration are reported.

Unsteady flow past a rotating circular cylinder at Reynolds numbers 103 and 104

1990 ◽  
Vol 220 ◽  
pp. 459-484 ◽  
Author(s):  
H. M. Badr ◽  
M. Coutanceau ◽  
S. C. R. Dennis ◽  
C. Ménard
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Unsteady Flow ◽  
Rotation Rate ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Number Range ◽  
Flow Past

The unsteady flow past a circular cylinder which starts translating and rotating impulsively from rest in a viscous fluid is investigated both theoretically and experimentally in the Reynolds number range 103 [les ] R [les ] 104 and for rotational to translational surface speed ratios between 0.5 and 3. The theoretical study is based on numerical solutions of the two-dimensional unsteady Navier–Stokes equations while the experimental investigation is based on visualization of the flow using very fine suspended particles. The object of the study is to examine the effect of increase of rotation on the flow structure. There is excellent agreement between the numerical and experimental results for all speed ratios considered, except in the case of the highest rotation rate. Here three-dimensional effects become more pronounced in the experiments and the laminar flow breaks down, while the calculated flow starts to approach a steady state. For lower rotation rates a periodic structure of vortex evolution and shedding develops in the calculations which is repeated exactly as time advances. Another feature of the calculations is the discrepancy in the lift and drag forces at high Reynolds numbers resulting from solving the boundary-layer limit of the equations of motion rather than the full Navier–Stokes equations. Typical results are given for selected values of the Reynolds number and rotation rate.

A note on the flow coefficients of capillary tube and small orifice restrictors exposed to very low Reynolds number flow

2005 ◽  
Vol 57 (3) ◽  
pp. 116-120 ◽  
Author(s):  
Suat Canbazoğlu ◽  
Fazıl Canbulut
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Capillary Tube ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Hydraulic Control ◽  
Capillary Tubes ◽  
Content Type ◽  
Control Devices ◽  
Low Reynolds

PurposeThe main objective of this study was to obtain the flow restricting capacity by determining their flow coefficients and to investigate the unsteady flow with low Reynolds number in the flow‐restricting devices such as orifices and capillary tubes having small diameters.Design/methodology/approachThere is an enormous literature on the flow of Newtonian fluids through capillaries and orifices particularly in many application fields of the mechanical and chemical engineering. But most of the experimental results in literature are given for steady flows at moderate and high Reynolds numbers (Re>500). In this study, the unsteady flow at low Reynolds number (10<Re<650) through flow‐restricting devices such as orifices and capillary tubes having very small diameters between 0.35 and 0.70 mm were experimentally investigated.FindingsThe capillary tubes have much more capillarity property with respect to equal diameter orifices. Increasing the ratio of capillary tube length to tube diameter and decreasing the ratio of orifice diameter to pipe diameter before orifice increase the throttling or restricting property of the orifices and the capillary tubes. The orifices can be preferred to the capillary tubes having the same diameter at the same system pressure for the hydraulic systems or circuits requiring small velocity variations. The capillary tubes provide higher pressure losses and they can be also used as hydraulic accumulators in hydraulic control devices to attenuate flow‐induced vibrations because of their large pressure coefficients. An important feature of the results obtained for capillary tubes and small orifices is that as the d/D for orifices increases and the L/d reduces for capillary tubes, higher values C are obtained and the transition from viscous to inertia‐controlled flow appears to take place at lower Reynolds numbers. This may be explained by the fact that for small orifices with high d/D ratios and for capillary tubes with small L/d ratios, the losses due to viscous shear are small. Another important feature of the results is that the least variations in C for small orifices and the higher variations in C for capillary tubes occur when the d/D and L/d ratios are smallest. This has favourable implications in hydraulic control devices since a constant value for the C may be assumed even at relatively low values of Re.Originality/valueTo the authors' knowledge, there is not enough information in the literature about the flow coefficients of unsteady flows through capillary tubes and small orifices at low Reynolds numbers. This paper fulfils this gap.

Three-Dimensional Simulation of Blood Flow in an Abdominal Aortic Aneurysm—Steady and Unsteady Flow Cases

1994 ◽  
Vol 116 (1) ◽  
pp. 89-97 ◽  
Author(s):  
Tad W. Taylor ◽  
Takami Yamaguchi
Keyword(s):  
High Pressure ◽  
Blood Flow ◽  
Abdominal Aortic Aneurysm ◽  
Aortic Aneurysm ◽  
Unsteady Flow ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Abdominal Aortic ◽  
Flow Cycle ◽  
Flow Case

Atherosclerosis and atherosclerotic aneurysms can occur in the abdominal aorta. Steady and unsteady three-dimensional flow cases were simulated in abdominal aortic aneurysm using a flow simulation package on a graphics workstation. In the steady case, three aneurysm models of 8.0 cm length were simulated using Reynolds numbers of 350 and 700. In the unsteady case, blood flow in a single asymmetric aneurysm of 8.0 cm length was simulated at Reynolds numbers of 350 and 700 and 1400. In the aneurysm center, two symmetric vortices were formed, and flow separation started at the aneurysm inlet. In the unsteady flow case, the main vortex appeared and disappeared and changed position in the unsteady flow case and induced vortices were formed. Although the centerline view shows the vortices change position with time, cross-sectional views show that two symmetric vortices are present or partially formed throughout the entire flow cycle. Regions of high pressure were observed at the aneurysm exit caused by the symmetric vortices that were formed, implying that this high-pressure region could be an area where rupture is most likely. In the unsteady case, regions of maximum pressure moved depending on the flow cycle time; at peak flow, local pressure maximums were observed at the distal aneurysm; these oscillated, tending to put an additional strain on the distal portion of the aneurysm. The shear stress was low in the aneurysm portion of the vessel, and local maximum values were observed at the distal aneurysm constriction.

Control Problem for Unsteady Magnetohydrodynamic Flow of Viscous Heat Conducting Fluid

2016 ◽  
Vol 685 ◽  
pp. 23-26 ◽  
Author(s):  
Dmitry Tereshko
Keyword(s):  
Unsteady Flow ◽  
Control Problem ◽  
Temperature Control ◽  
Reynolds Numbers ◽  
Conducting Fluid ◽  
Heat Conducting ◽  
Electrically Conducting ◽  
Finite Dimensional ◽  
Electrically Conducting Fluid ◽  
Viscous Heat

This work is devoted to control problem for unsteady flow of heat and electrically conducting fluid at small magnetic Reynolds numbers. This problem is connected with vortex reduction using temperature control on some parts of the boundary. Numerical algorithm based on finite-dimensional minimization is proposed and numerical results are discussed.

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