scholarly journals Ferrofluid thin films for aerofoil lift enhancement and delaying flow separation

2020 ◽  
Vol 124 (1282) ◽  
pp. 1865-1878
Author(s):  
F.J. Arias
Keyword(s):  
Thin Films ◽  
Boundary Layer ◽  
Flow Separation ◽  
Unit Surface Area ◽  
Moving Wall ◽  
Air Stream ◽  
Unit Surface ◽  
Weight Penalty ◽  
Lift Enhancement ◽  
Novel Concept

ABSTRACTIn this work, consideration is given to a novel concept for aerofoil lift enhancement and delaying flow separation. Here, lift enhancement is attained by preventing the growth of the boundary layer through the elimination of the zero-slip condition between the wing surface and the air stream. The concept would simulate all the effects of a moving wall, leading to the appearance of a slip velocity at the gas–fluid interface, including the injection of momentum into the air boundary layer, but with one exception: here there is no moving wall but instead a ferrofluid thin film pumped parallel and attached to the wall by a magnetic field. Utilising a simplified physical model for the velocity profile of the ferrofluid film and based on ferrohydrodynamic stability considerations, an analytical expression for the interfacial velocity is derived. Finally, from the available experimental data on moving walls, the expected lift and angle-of-attack enhancement are found as well as the weight penalty per unit surface area of the wing is estimated. Additional research and development is required to explore the possibilities of using ferrofluid thin films.

Ferrofluid  Thin Films for Airfoil  Lift Generation

2020 ◽  
Author(s):  
Francisco Arias
Keyword(s):  
Magnetic Field ◽  
Thin Film ◽  
Thin Films ◽  
Boundary Layer ◽  
Slip Velocity ◽  
Fluid Interface ◽  
Interfacial Velocity ◽  
Moving Wall ◽  
Air Stream ◽  
Novel Concept

Abstract In this work, consideration is given to a novel concept for airfoil lift generation and flow control. In this concept, the goal is attained by preventing the growth of the boundary layer from the elimination of the zero slip condition between the surface and the air stream. The concept would simulate all effects of a moving wall leading in the appearance of slip velocity in the gas-fluid interface including the injection of momentum into the boundary layer, with one exception: there is no moving wall but instead a ferrofluid thin film attached at the wall by a magnetic field which permit to attain much more higher velocities at the interface which is not allowable if mobil surface wall are used. Utilizing a simplified physical model for the profile velocity of the ferrofluid film and from ferrohydrodynamic stability considerations an analytical expression for the interfacial velocity was derived. Finally, from the available experimental data on moving walls the expected lift and attack angle enhancement was found. Additional R\&D is required in order to explore the possibilities in the use of ferrofluid thin films.

scholarly journals The flow separation delay in the boundary layer by induced vortices

2016 ◽  
Vol 20 (2) ◽  
pp. 251-261 ◽  
Author(s):  
Ishtiaq A. Chaudhry ◽  
Tipu Sultan ◽  
Farrukh A. Siddiqui ◽  
M. Farhan ◽  
M. Asim
Keyword(s):  
Boundary Layer ◽  
Flow Separation

Boundary Layer Flashback Model for Hydrogen Flames in Confined Geometries Including the Effect of Adverse Pressure Gradient

2020 ◽  
Author(s):  
Ólafur H. Björnsson ◽  
Sikke A. Klein ◽  
Joeri Tober
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Flow Separation ◽  
Gradient Flow ◽  
Lewis Number ◽  
Adverse Pressure Gradient ◽  
Future Research ◽  
Diffuser Flow ◽  
Combustion Properties ◽  
Quenching Distance

Abstract The combustion properties of hydrogen make premixed hydrogen-air flames very prone to boundary layer flashback. This paper describes the improvement and extension of a boundary layer flashback model from Hoferichter [1] for flames confined in burner ducts. The original model did not perform well at higher preheat temperatures and overpredicted the backpressure of the flame at flashback by 4–5x. By simplifying the Lewis number dependent flame speed computation and by applying a generalized version of Stratford’s flow separation criterion [2], the prediction accuracy is improved significantly. The effect of adverse pressure gradient flow on the flashback limits in 2° and 4° diffusers is also captured adequately by coupling the model to flow simulations and taking into account the increased flow separation tendency in diffuser flow. Future research will focus on further experimental validation and direct numerical simulations to gain better insight into the role of the quenching distance and turbulence statistics.

Flow and Heat Transfer in Branched Wavy Microchannels

2013 ◽  
Author(s):  
Pawan K. Singh ◽  
Hua Feng Samuel Tan ◽  
Chiang Juay Teo ◽  
Poh Seng Lee
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Aspect Ratio ◽  
Chaotic Advection ◽  
Wavy Channel ◽  
Flow And Heat Transfer ◽  
Boundary Layer Development ◽  
Novel Concept ◽  
High Pressure Zone ◽  
Wavy Channels

The Wavy channels are supposed to enhance performance of microchannel heat sink through chaotic advection. The change in boundary layer thickness (thinning) and the macroscopic mixing due to the formation of Dean’s vortices have been found to be main reasons for enhanced heat transfer in wavy microchannel. Present study carries out a detailed numerical investigation for flow and heat transfer in wavy channel. A 3D geometry for a single loop of wavy channel is modeled in GAMBIT and simulated in CFD software FLUENT. The basic dimensions were 0.15 mm width, 0.3 mm height and 1.5 mm length. The formation of Dean vortices are shown. In parametric study, the effect of Re number on the flow and heat transfer performance is shown. Heat transfer was found to be increased with Re. The effect of Aspect ratio is shown. The channel with the aspect ratio of 0.5 is found to be best among the channels studied including wavy and straight microchannels. A novel concept of secondary branches is introduced to wavy microchannel to take advantage of high pressure zone at crust. The branched wavy microchannel encouraged the secondary flow thus enhanced the macroscopic mixing. Due to disrupt of boundary layer development and its re-initialization, an improved thermal performance was achieved.

scholarly journals Mpemba Effect- the Effect of Time

2021 ◽  
Author(s):  
Jianan Wang
Keyword(s):  
Gravitational Field ◽  
Surface Area ◽  
Time Effect ◽  
Light Quantum ◽  
Unit Surface Area ◽  
Heat Flows ◽  
Unit Surface ◽  
Average Wavelength ◽  
Nature Of Time ◽  
The Relationship

This paper draws the following conclusions on the nature of time by analyzing the relationship between time and speed, the relationship between time and gravitational field, the gravitational redshift of the photon, and the black-body radiation theorem: Time on an object is proportional to the amount of energy flowing out (or in) per unit time (observer’s time) per unit surface area of the object. When an object radiates energy outward: t'=μB(T) =μσT 4=μnhν/st Where t’ is the time on the object, μ is a constant, B(T) is the radiosity，the total energy radiated from the unit surface area of the object in unit time (observer’s time), σ is the Stefan-Boltzmann constant, T is the absolute temperature, n is the number of the photons radiated, ν is the average frequency of the photons radiated, s is the surface area of the object and t is the time on the observer. When the object radiates energy outward, the higher the energy density of the space (for example the stronger the gravitational field of the space), the smaller the radiosity B(T) of the object in the space, the longer the average wavelength of the light quantum emitted by the object, the slower the time on the object, the longer the life of the system. When the object radiates energy outward, the faster the object moves relative to the ether, the higher the energy density of the local space in which the object is located, the smaller the radiosity B(T) of the object, the longer the average wavelength of the light quantum radiated by the object, the slower the time on the object, and the longer the life of the system. When the object radiates energy outward, the higher the temperature of the object, the greater the object's radiosity B(T), the shorter the average wavelength of the light quantum radiated by the object, the faster the time on the object, and the shorter the life of the system. Applying the above conclusions about the nature of time, the author analyzes the Mpemba effect and the inverse Mpemba effect, and reaches the following conclusion: the Mpemba effect is the time effect produced when heat flows from objects into space, and the "inverse" Mpemba effect is the time effect produced when heat flows from space into objects.

Flow Separation

2009 ◽  
Author(s):  
Ahmad Fakheri
Keyword(s):  
Boundary Layer ◽  
Nusselt Number ◽  
Drag Coefficient ◽  
Numerical Solution ◽  
Flow Separation ◽  
Potential Flow ◽  
Experimental Results ◽  
Science Courses ◽  
Boundary Layer Equations ◽  
Solution Of Equations

In thermal science courses, flow over curved objects, like cylinders or spheres are generally discussed qualitatively, followed by the presentation of numerical or experimental results for the drag coefficient, Nusselt number, and flow separation. Rarely, there is much discussion of how solutions are obtained. In this paper the flow separation is first introduced by solving the Falkner-Skan flow. The process for numerical solution of equations is presented to show that the flow separates at a plate angle of about −18°. Comparisons are drawn between this and flow over a cylinder. The non-similar boundary layer equations are then solved flow over a cylinder, using potential flow results for the velocity outside of the boundary layer. This solution shows that the flow separates at 103.5°, which is significantly more than the experimental value of 80°. Using a more realistic velocity for flow outside of the boundary layer, the numerical solution obtained predicts flow separation at an angle of 79°, which is close to the experimental results. All the solutions are obtained using spreadsheets that greatly simplify the analysis.

Long-term experimental study of the aquatic plant system for polluted river water

2002 ◽  
Vol 46 (11-12) ◽  
pp. 217-224 ◽  
Author(s):  
K. Sato ◽  
H. Sakui ◽  
Y. Sakai ◽  
S. Tanaka
Keyword(s):  
Surface Area ◽  
Aquatic Plant ◽  
Aquatic Macrophyte ◽  
Unit Surface Area ◽  
Artificial Wetlands ◽  
Polluted River ◽  
Plant System ◽  
Unit Surface ◽  
Experimental Facilities

Water purification using artificial wetlands and aquatic macrophyte is attracting attention as a purification technology that can create rich ecosystems while imposing a minimal load on the environment. Because an aquatic plant system requires a large surface area, design specifications and maintenance methods that can obtain the optimum purification effect per unit surface area must be established. Large experimental facilities have been constructed beside a polluted river flowing into Lake Kasumigaura and have been used for a three-year experiment using several kinds of aquatic plants. This report summarizes the characteristics and the design load of the aquatic plant system based on this study and results from other aquatic plant facilities.

Sign in / Sign up

Export Citation Format

Share Document