scholarly journals Aerodynamics of Flapping Wing at Low Reynolds Numbers: Force Measurement and Flow Visualization

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Abhijit Banerjee ◽  
Saurav K. Ghosh ◽  
Debopam Das
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Flow Visualization ◽  
Force Measurement ◽  
Reynolds Numbers ◽  
Flapping Flight ◽  
Water Tank ◽  
Cross Sectional ◽  
Piv Measurement ◽  
The Difference

Flow field of a butterfly mimicking flapping model with plan form of various shapes and butterfly-shaped wings is studied. The nature of the unsteady flow and embedded vortical structures are obtained at chord cross-sectional plane of the scaled wings to understand the dynamics of insect flapping flight. Flow visualization and PIV experiments are carried out for the better understanding of the flow field. The model being studied has a single degree of freedom of flapping. The wing flexibility adds another degree to a certain extent introducing feathering effect in the kinematics. The mechanisms that produce high lift and considerable thrust during the flapping motion are identified. The effect of the Reynolds number on the flapping flight is studied by varying the wing size and the flapping frequency. Force measurements are carried out to study the variations of lift forces in the Reynolds number (Re) range of 3000 to 7000. Force experiments are conducted both at zero and finite forward velocity in a wind tunnel. Flow visualization as well as PIV measurement is conducted only at zero forward velocity in a stagnant water tank and in air, respectively. The aim here is to measure the aerodynamic lift force and visualize the flow field and notice the difference with different Reynolds number (Re), and flapping frequency (f), and advance ratios (J=U∞/2ϕfR).

An almost-inviscid geostrophic flow

1962 ◽  
Vol 12 (1) ◽  
pp. 129-134 ◽  
Author(s):  
L. M. Hocking
Keyword(s):  
Reynolds Number ◽  
Fluid Velocity ◽  
Equations Of Motion ◽  
Axial Direction ◽  
Reynolds Numbers ◽  
Rigid Rotation ◽  
Velocity Variation ◽  
Geostrophic Flow ◽  
The Difference ◽  
Streaming Motion

An almost rigid rotation of a viscous fluid is produced by dividing the containing cylinder into two sections and rotating them at slightly different speeds. The fluid velocity can be separated into two parts, a swirl about the axis and a streaming motion in the axial planes. When the difference in the speeds of rotation of the two sections is small, the equations of motion can be linearized. The solution is found for large Reynolds numbers and provides an illustration of the way in which the conditions of geostrophic flow (no velocity variation in the axial direction and an inability to insist on undistrubed flow at infinity) are approached as the Reynolds number tends to infinity.

Numerical Investigation on Turbulence Statistics and Heat Transfer of a Circular Jet Impinging on a Roughened Flat Plate

2021 ◽  
Vol 13 (4) ◽  
Author(s):  
Abdulrahman Alenezi ◽  
Abdulrahman Almutairi ◽  
Hamad Alhajeri ◽  
Abdulaziz Gamil ◽  
Faisal Alshammari
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Roughness Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Target Plate ◽  
Cross Sectional ◽  
Flow Physics ◽  
Baseline Case

Abstract A detailed heat transfer numerical study of a three-dimensional impinging jet on a roughened isothermal surface is presented and is investigated from flow physics vantage point under the influence of different parameters. The effects of the Reynolds number, roughness location, and roughness dimension on the flow physics and heat transfer parameters are studied. Additionally, the relations between average heat transfer coefficient (AHTC) and flow physics including pressure, wall shear and flow vortices with thermodynamic nonequilibrium are offered. This paper studies the effect of varying both location and dimension of the roughness element which took the shape of square cross-sectional continuous ribs to deliver a favorable trade-off between total pressure loss and heat transfer rate. The roughness element was tested for three different radial locations (R/D) = 1, 1.5, and 2 and at each location its height (i.e., width) (e) was changed from 0.25 to 1 mm in incremental steps of 0.25. The study used a jet angle (α) of 90 deg, jet-to-target distance (H/D = 6), and Re ranges from 10,000 to 50,000, where H is the vertical distance between the target plate and jet exit. The results show that the AHTC can be significantly affected by changing the geometry and dimensions of the roughness element. This variation can be either an augmentation of, or decrease in, the (HTC) when compared with the baseline case. An enhancement of 12.9% in the AHTC was achieved by using optimal location and dimensions of the roughness element at specific Reynolds number. However, a diminution between 10% and 30% in (AHTC) was attained by the use of rib height e = 1 mm at Re = 50k. The variation of both rib location and height showed better contribution in increasing heat transfer for low-range Reynolds numbers.

Force on a Small Particle Attached to a Plane Wall in a Hiemenz Straining Flow

2012 ◽  
Vol 134 (11) ◽  
Author(s):  
A. B. Maynard ◽  
J. S. Marshall
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Reynolds Numbers ◽  
Lower Surface ◽  
Ring Structure ◽  
Plane Wall ◽  
Small Reynolds Numbers ◽  
Particle Force ◽  
Volume Method ◽  
Excellent Accuracy

The force acting on a spherical particle fixed to a wall and immersed in an axisymmetric straining flow is examined for small Reynolds numbers. The steady, incompressible flow field is computed using an axisymmetric finite-volume method over conditions spanning five decades in the Reynolds number. The flow is characterized by the formation of a vortex ring structure in the wedge region formed between the particle lower surface and the plane wall. A power law expression for the dimensionless particle force is obtained as a function of the Reynolds number, which is found to hold with excellent accuracy for Reynolds numbers below about 0.1.

Numerical Investigation on Visualizations of Confined Air Flow in a Slot Jet Inside a Rectangular Channel

2015 ◽  
Vol 813-814 ◽  
pp. 736-741
Author(s):  
M. Muthukannan ◽  
P. Rajesh Kanna ◽  
S. Jeyakumar ◽  
J.Y. Raja Shangaravel ◽  
S. Raghu ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Numerical Investigation ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Vortex Center ◽  
Computational Domain ◽  
Reattachment Length ◽  
Aspect Ratios ◽  
Air Jet

In the present numerical investigation, the flow field of confined slot air jet in a rectangular computational domain is reported. In the present work the flow field parameters like reattachment length, vortex center and horizontal velocity profiles for various Reynolds numbers and for various aspect ratios are presented .The present study reveals that the vortex centers are moving in a downstream direction with increase in Reynolds number. The reattachment length is directly dependent on the Reynolds numbers. In case of vortex dynamics, the vortex size is indirectly dependent on the inlet jet width. In the present investigation, SIMPLE algorithm is used to solve the governing equations. It is concluded that the aspect ratio and the Reynolds number are playing dominant roles in flow field of the present computational domain.

scholarly journals PIV measurement of complex flow characteristics in open-cell metal foam replica

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Minsin Kim ◽  
Youngwoo Kim ◽  
Sajjad Hosseini ◽  
Kyung Chun Kim
Keyword(s):  
Reynolds Number ◽  
Metal Foam ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Complex Flow ◽  
Time Resolved ◽  
Open Cell ◽  
Flow Disturbances ◽  
Piv Measurement ◽  
Inlet Conditions

Time-resolved 2-D particle image velocimetry was used to study on turbulent flow characteristics inside an open-cell metal foam under the laminar and turbulent inlet conditions. A study on the effect of Reynolds number was conducted with different three channel Reynolds numbers, 1000, 5000 and 10000. Uniform upstream flow is divided by the pore network of metal foam and it is found that there are flow disturbances induced by metal foam structure even at a laminar inlet condition. It is confirmed that there is a similarity of the preferred flow path flows take regardless of Reynolds number.

scholarly journals Effect of Ambient Reynolds Number on Small Wind Turbine Subjected to Low Wind Speed Conditions

2021 ◽  
Vol 12 (2) ◽  
pp. 223-231
Author(s):  
Joel Mbwiga ◽  
Cuthbert Z Kimambo ◽  
Joseph Kihedu
Keyword(s):  
Reynolds Number ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Reynolds Numbers ◽  
Design Parameters ◽  
Power Performance ◽  
Airfoil Surface ◽  
Small Wind Turbine ◽  
Low Wind Speed ◽  
The Difference

Wind flow over the airfoil surface is adversely affected by the differences between the design and ambient values of a dimensionless quantity called Reynolds number. Wind turbine designed for high Reynolds Number shows lower maximum power performance when installed in low-speed wind regime. Tanzanian experience shows that some imported modern wind turbines depict lower power performance compared to the drag-type locally manufactured wind turbines. The most probable reason is the difference between design and local ambient Reynolds numbers. The turbine design parameters have their properties restricted to the range of Reynolds numbers for which the turbine was designed for. When a wind turbine designed for a certain range of Reynolds numbers is made to operate in the Reynolds number out of that range, it behaves differently from the embodied design specifications. The small wind turbine of higher Reynolds number will suffer low lift forces with probably occasional stalls.  

Effects of Reynolds Number on Drag Reduction in T-Junction Pipes due to Small Obstacles

2011 ◽  
Author(s):  
Toshitake Ando ◽  
Toshihiko Shakouchi ◽  
Yoshitaka Suzuki ◽  
Koichi Tsujimoto
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Flow Resistance ◽  
Vortex Flow ◽  
Reynolds Numbers ◽  
Counter Flow ◽  
Cross Sectional ◽  
Simple Method ◽  
Pipe Flows ◽  
Large Flow

T-junction pipes are used to distribute one flow into two flows or join two flows into one flow. Separated vortex flow regions near the corners of junctions are caused in these types of flows. They reduce the effective cross-sectional area of the pipe flows and then create large flow resistance or drag. The corners of junctions are generally rounded to avoid flow separation and reduce flow resistance. We tried to reduce the flow resistance of counter-flow T-junction pipes in which two flows in the opposite direction entered the junction, mixed, and then vertically flowed out together by using a simple method. We mounted two small weir-shaped obstacles on the walls of the two upstream pipes by the side around the junction corners, which is a new way we propose of controlling flow separation. The pressure distribution along the pipes was measured and the drag of the T-junction pipe was estimated. Additionally, the effects of the Reynolds number on the flow resistance and its rate of reduction by mounting small obstacles were clarified. The two major results we obtained were: (1) the flow resistance of T-junctions could be reduced by about a maximum of 30% by mounting small obstacles at heights of 0.30 D and 0.47 D (D: pipe diameter) from the upstream of the corner. We also found (2) the rate of reduction in flow resistance increased with decreasing Reynolds numbers between 5–10 × 104, but this decreased rapidly between 2.5–5 × 104.

A Bidirectional Valveless Piezoelectric Micropump With Double Chambers Applying Synthetic Jet

2015 ◽  
Author(s):  
Xitong Zhang ◽  
Song Yang ◽  
Xiuhua He ◽  
Shouqi Yuan
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Flow Field ◽  
Simple Structure ◽  
Piezoelectric Actuators ◽  
Reynolds Numbers ◽  
Synthetic Jet ◽  
Volume Changes ◽  
Sinusoidal Vibration ◽  
Sst Turbulence Model

A novel bidirectional valveless piezoelectric micropump with double chambers applying synthetic jet effect was developed. The numerical simulation was applied to study the performance and flow field of the micropump. The micropump consisted of a pump body, a cover and two piezoelectric actuators had a simple structure. The direction of the flow of the micropump could change immediately based on the Coanda effect by controlling the displacement of the two piezoelectric actuators. And the synthetic jet element increase the flowrate greatly. The effects of the Reynolds number and frequency on the flowrate were studied. The size of the throat was 200 μm × 200 μm. The Reynolds numbers were 500 and 1000 in the simulation and the SST turbulence model was chosen. The sinusoidal vibration was applied and the frequency ranged from 10 to 50 Hz. The results showed that the flowrate of jet entrainment accounted for more than 80% of the outlet flowrate. And the outlet flowrates were much larger than the volume changes of the pump chambers. The fluctuation of flowrate decreased with the increase of frequency. The micropump could achieve continuous outflow as the frequency was higher than 30 Hz.

Experimental Investigation of the Fluid Motion in a Cylinder Driven by a Flat-Plate Impeller

2006 ◽  
Vol 129 (6) ◽  
pp. 737-746 ◽  
Author(s):  
Douglas Bohl
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Reverse Flow ◽  
Fluid Motion ◽  
Reynolds Numbers ◽  
Cylinder Wall ◽  
Water Mixture ◽  
Recirculating Flow ◽  
Blade Tip ◽  
High Reynolds

The flow field in a cylindrical container driven by a flat-bladed impeller was investigated using particle image velocimetry (PIV). A range of Reynolds numbers (0.005–7200), based on the container radius rw, were investigated using four Newtonian fluids: water (Re=7200,6800), 85/15 glycerin/water mixture (Re=108), pure glycerin (Re=8), and corn syrup (Re=0.02,0.005). Two impellers with a radius of 0.43rw and 0.95rw were used to drive the flow. The 0.43rw impeller was shown to generate a vortex near the tip of the blades. The peak magnitude of the vortices and the size of the vortices in the radial direction decreased with increasing Reynolds number. Additionally, the vortex generated at the high Reynolds number was unsteady with a trailing shear layer that periodically shed vorticity into the flow field. The structure of the flow in the region between the blade and the cylinder wall showed a Reynolds number dependence, though the two lowest Reynolds number (0.02 and 8) flows investigated had quantitatively similar flow structures. These cases were found to have a closed region of reverse flow between the blade tip and the cylinder wall. No recirculating flow was indicated for the Re=108 and 7200 cases. These data indicate that there may be a critical condition below which there is little dependence in the flow structure on the Reynolds number.

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