The Effect of Boat-Tailing on the Flow Round a Two-Dimensional Blunt-Based Aerofoil at Zero Incidence

1967 ◽  
Vol 71 (684) ◽  
pp. 854-858 ◽  
Author(s):  
D. J. Maull ◽  
B. J. Hoole
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Pressure Distribution ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Base Pressure ◽  
Two Dimensional ◽  
Flow Round ◽  
Low Speeds

SummarySome experiments on the effect of boat-tailing on the pressure distribution round blunt-based aerofoils are described. The experiments were carried out at low speeds at a Reynolds number of 1.5 X 105. The wake was investigated with attention being paid to the vortex shedding, and to the distance downstream of the base where vortices form.It is shown that the theory due to Nash predicts the effect of boat-tailing on base pressure quite well and that a correlation of drag coefficient, Strouhal number and base pressure proposed by Bearman applies to the models tested here.

Effects of Corner Cutoffs on Flow Past Two Square Cylinders in a Tandem Arrangement

2012 ◽  
Author(s):  
Y. T. Krishne Gowda ◽  
H. V. Ravindra ◽  
C. K. Vikram
Keyword(s):  
Reynolds Number ◽  
Pressure Distribution ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Two Dimensional ◽  
Square Cylinder ◽  
Tandem Arrangement ◽  
Square Cylinders ◽  
Flow Past

Flow past the two square cylinders with and without corner modification in a tandem arrangement has been simulated using a CFD code FLUENT. A Reynolds number of 100 and pitch to perimeter ratios (PPR) of 2,4 and 6 are considered for the investigation. The flow is assumed to be two dimensional unsteady and incompressible. The obtained results are presented in the form of streamlines, pressure distribution, monitored velocity, lift coefficient and Strouhal number. Results indicate, in case of chamfered and rounded corners, there is decrease in the wake width and thereby the lift values. For the square cylinders of same perimeters with and without corner modification, the size of the eddy and the monitored velocity in between the square cylinders increases with increase in PPR. Frequency of vortex shedding is same in between the cylinders and in the downstream of the cylinder. Frequency of vortex shedding decreases with the introduction of second cylinder either in the upstream or downstream of the first cylinder. The lift coefficient of square cylinder with corner modification decreases but Strouhal number increases when compared with a square cylinder without corner modification.

scholarly journals The onset of unsteadiness of two-dimensional bodies falling or rising freely in a viscous fluid: a linear study

2011 ◽  
Vol 690 ◽  
pp. 173-202 ◽  
Author(s):  
Pauline Assemat ◽  
David Fabre ◽  
Jacques Magnaudet
Keyword(s):  
Reynolds Number ◽  
Viscous Fluid ◽  
Strouhal Number ◽  
Cross Section ◽  
Vortex Shedding ◽  
The Body ◽  
Mode Switching ◽  
Two Dimensional ◽  
Body Dynamics ◽  
Mass Ratios

AbstractWe consider the transition between the steady vertical path and the oscillatory path of two-dimensional bodies moving under the effect of buoyancy in a viscous fluid. Linearization of the Navier–Stokes equations governing the flow past the body and of Newton’s equations governing the body dynamics leads to an eigenvalue problem, which is solved numerically. Three different body geometries are then examined in detail, namely a quasi-infinitely thin plate, a plate of rectangular cross-section with an aspect ratio of 8, and a rod with a square cross-section. Two kinds of eigenmodes are observed in the limit of large body-to-fluid mass ratios, namely ‘fluid’ modes identical to those found in the wake of a fixed body, which are responsible for the onset of vortex shedding, and four additional ‘aerodynamic’ modes associated with much longer time scales, which are also predicted using a quasi-static model introduced in a companion paper. The stability thresholds are computed and the nature of the corresponding eigenmodes is investigated throughout the whole possible range of mass ratios. For thin bodies such as a flat plate, the Reynolds number characterizing the threshold of the first instability and the associated Strouhal number are observed to be comparable with those of the corresponding fixed body. Other modes are found to become unstable at larger Reynolds numbers, and complicated branch crossings leading to mode switching are observed. On the other hand, for bluff bodies such as a square rod, two unstable modes are detected in the range of Reynolds number corresponding to wake destabilization. For large enough mass ratios, the leading mode is similar to the vortex shedding mode past a fixed body, while for smaller mass ratios it is of a different nature, with a Strouhal number about half that of the vortex shedding mode and a stronger coupling with the body dynamics.

A First Attempt to Numerically Compute Forces on Birds in V Formation

2010 ◽  
Vol 16 (3) ◽  
pp. 245-258 ◽  
Author(s):  
C. M. Sewatkar ◽  
Atul Sharma ◽  
Amit Agrawal
Keyword(s):  
Reynolds Number ◽  
Simple Model ◽  
Drag Coefficient ◽  
Energy Saving ◽  
Strouhal Number ◽  
Lateral Force ◽  
Incoming Flow ◽  
Two Dimensional

A model for studying the flow forces experienced by cylinders placed in V formation is presented, and an elementary comparison with flocking birds is made. The cylinders are modeled as two-dimensional square bodies exposed to incoming flow at Reynolds number 100. The effects of angle of formation (α), streamwise spacing (Ss), and number of cylinders (N) on parameters such as the coefficient of drag, coefficient of lateral force, and Strouhal number are studied. It is observed that the drag experienced by the cylinders decreases with a decrease in the angle of formation. The leading cylinder experiences the smallest drag, irrespective of the angle. The drag becomes less than the drag on an isolated cylinder at certain angles depending on the position of the cylinder in the formation. The average drag on cylinders in V formation is found to be less than on an isolated cylinder, leading to energy saving when flying in formation. It is also noted that the cylinders experience a substantial lateral force. Study of this simple model may help better understand certain features of flocking birds.

scholarly journals Lattice gas automaton modelling of a vortex flow meter: Strouhal–Reynolds number dependence

2017 ◽  
Vol 56 (4) ◽  
pp. 191-199
Author(s):  
Vaidas Juknevičius ◽  
Jogundas Armaitis
Keyword(s):  
Reynolds Number ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Vortex Flow ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Flow Meter ◽  
Reynolds Number Dependence

Motivated by recent experimental and computational results concerning a three-dimensional structure of vortices behind a vortex shedding flow meter [M. Reik et al., Forsch. Ingenieurwes. 74, 77 (2010)], we study the Strouhal–Reynolds number dependence in the vortex street in two dimensions behind a trapezoid-shaped object by employing two types of Frisch–Hasslacher–Pomeau (FHP) models. Our geometry is intended to reproduce the operation of a vortex shedding flow meter in a two-dimensional setting, thus preventing the formation of a three-dimensional vortex structure. In particular, we check if the anomalous Reynolds–Strouhal number dependence reported for three dimensions can also be found in our two-dimensional simulation. As we find that the Strouhal number is nearly independent of the Reynolds number in this particular setup, our results provide support for the hypothesis that three-dimensional flow structures are responsible for that dependence, thus hinting at the importance of the pipe diameter to the accurate operation of industrial vortex flow meters.

Numerical analysis of two-dimensional motion of a freely falling circular cylinder in an infinite fluid

2008 ◽  
Vol 604 ◽  
pp. 33-53 ◽  
Author(s):  
KAK NAMKOONG ◽  
JUNG YUL YOO ◽  
HYOUNG G. CHOI
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Velocity Vector ◽  
Density Ratio ◽  
Transverse Motion ◽  
Stream Velocity ◽  
Gravitational Acceleration ◽  
Two Dimensional

The two-dimensional motion of a circular cylinder freely falling or rising in an infinite fluid is investigated numerically for the range of Reynolds number Re, < 188 (Galileo number G < 163), where the wake behind the cylinder remains two-dimensional, using a combined formulation of the governing equations for the fluid and the dynamic equations for the cylinder. The effect of vortex shedding on the motion of the freely falling or rising cylinder is clearly shown. As the streamwise velocity of the cylinder increases due to gravity, the periodic vortex shedding induces a periodic motion of the cylinder, which is manifested by the generation of the angular velocity vector of the cylinder parallel to the cross-product of the gravitational acceleration vector and the transverse velocity vector of the cylinder. Correlations of the Strouhal–Reynolds-number and Strouhal–Galileo-number relationship are deduced from the results. The Strouhal number is found to be smaller than that for the corresponding fixed circular cylinder when the two Reynolds numbers based on the streamwise terminal velocity of the freely falling or rising circular cylinder and the free-stream velocity of the fixed one are the same. From numerical experiments, it is shown that the transverse motion of the cylinder plays a crucial role in reducing the Strouhal number. The effect of the transverse motion is similar to that of suction flow on the low-pressure side, where a vortex is generated and then separates, so that the pressure on this side recovers with the vortex separation retarded. The effects of the transverse motion on the lift, drag and moment coefficients are also discussed. Finally, the effect of the solid/fluid density ratio on Strouhal–Reynolds-number relationship is investigated and a plausible correlation is proposed.

Aerodynamics of a two-dimensional bluff body with the cross-section of a train

2020 ◽  
Vol 23 (12) ◽  
pp. 2679-2693 ◽  
Author(s):  
Huan Li ◽  
Xuhui He ◽  
Hanfeng Wang ◽  
Si Peng ◽  
Shuwei Zhou ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Large Amplitude ◽  
High Speed ◽  
Bluff Body ◽  
Mean Amplitude ◽  
Two Dimensional ◽  
Aerodynamic Forces ◽  
Moderate Reynolds Number ◽  
Amplitude Mode

Experiments on the aerodynamics of a two-dimensional bluff body simplified from a China high-speed train in crosswinds were carried out in a wind tunnel. Effects of wind angle of attack α varying in [−20°, 20°] were investigated at a moderate Reynolds number Re = 9.35 × 104 (based on the height of the model). Four typical behaviors of aerodynamics were identified. These behaviors are attributed to the flow structure around the upper and lower halves of the model changing from full to intermittent reattachment, and to full separation with a variation in α. An alternate transition phenomenon, characterized by an alteration between large- and small-amplitude aerodynamic fluctuations, was detected. The frequency of this alteration is about 1/10 of the predominant vortex shedding. In the intervals of the large-amplitude behavior, aerodynamic forces fluctuate periodically with a strong span-wise coherence, which are caused by the anti-symmetric vortex shedding along the stream-wise direction. On the contrary, the aerodynamic forces fluctuating at small amplitudes correspond to a weak span-wise coherence, which are ascribed to the symmetric vortex shedding from the upper and lower halves of the model. Generally, the mean amplitude of the large-amplitude mode is 3 times larger than that of the small one. Finally, the effects of Reynolds number were examined within Re = [9.35 × 104, 2.49 × 105]. Strong Reynolds number dependence was observed on the model with two rounded upper corners.

An Experimental Investigation of the Wake of an Axisymmetric Body with a Slanted Base

1983 ◽  
Vol 34 (1) ◽  
pp. 24-45 ◽  
Author(s):  
X.J. Xia ◽  
P.W. Bearman
Keyword(s):  
Drag Coefficient ◽  
Vortex Shedding ◽  
Free Stream ◽  
Sudden Change ◽  
Base Pressure ◽  
Wake Flow ◽  
Main Body ◽  
Angle Of Incidence ◽  
Slant Angle ◽  
Free Stream Turbulence

SummaryThe effect of base slant on the base pressure distribution, drag coefficient and vortex shedding characteristics of a model consisting of an axisymmetric main body with an ellipsoidal nose have been investigated for three fineness ratios; 3, 6 and 9. A sudden change in the drag coefficient and separated flow pattern is observed at a critical slant angle (for constant incidence) or at a critical angle of incidence (for a constant base slant angle). The tests confirm that the value of the maximum drag coefficient is extremely sensitive to angle of incidence. Measurements of the frequency of vortex shedding are presented and the structure of the wake is investigated using smoke visualization and hot-wire correlation measurements. The wake is found to be far less stable than that from a two-dimensional bluff body and the vortex structures are sometimes in-phase and sometimes out of phase across the wake. The effect of free-stream turbulence on this family of body shapes is observed to be different to that on three-dimensional blunt-faced bluff bodies. Free-stream turbulence is found to have a minimal effect on base pressure for slant angles giving a recirculating type near wake flow. When longitudinal vortices are present the addition of free-stream turbulence slightly reduces the magnitude of the peak suctions recorded on the base but has little effect on base drag.

Effect of Compressibility on Gaseous Flows in a Micro-Tube

2003 ◽  
Author(s):  
Yutaka Asako ◽  
Kenji Nakayama
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Pressure Distribution ◽  
Flow Characteristics ◽  
Fused Silica ◽  
Two Dimensional ◽  
Arbitrary Lagrangian Eulerian ◽  
Gaseous Flow ◽  
Gaseous Flows ◽  
Energy Equations

The product of friction factor and Reynolds number (f·Re) of gaseous flow in the quasi-fully developed region of a micro-tube was obtained experimentally and numerically. The tube cutting method was adopted to obtain the pressure distribution along the tube. The fused silica tubes whose nominal diameters were 100 and 150 μm, were used. Two-dimensional compressible momentum and energy equations were solved to obtain the flow characteristics in micro-tubes. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The both results agree well and it was found that (f·Re) is a function of Mach number.

Two- and Three-Dimensional Simulations of the Flow Around a Cylinder Fitted With Strakes

2012 ◽  
Author(s):  
Bruno S. Carmo ◽  
Rafael S. Gioria ◽  
Ivan Korkischko ◽  
Cesar M. Freire ◽  
Julio R. Meneghini
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Free Stream ◽  
Three Dimensional ◽  
The Body ◽  
Vortex Wake ◽  
Two Dimensional ◽  
Flow Around A Cylinder ◽  
Three Dimensional Simulations ◽  
Angle Of Rotation

Two- and three-dimensional simulations of the flow around straked cylinders are presented. For the two-dimensional simulations we used the Spectral/hp Element Method, and carried out simulations for five different angles of rotation of the cylinder with respect to the free stream. Fixed and elastically-mounted cylinders were tested, and the Reynolds number was kept constant and equal to 150. The results were compared to those obtained from the simulation of the flow around a bare cylinder under the same conditions. We observed that the two-dimensional strakes are not effective in suppressing the vibration of the cylinders, but also noticed that the responses were completely different even with a slight change in the angle of rotation of the body. The three-dimensional results showed that there are two mechanisms of suppression: the main one is the decrease in the vortex shedding correlation along the span, whilst a secondary one is the vortex wake formation farther downstream.

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