Flow and HydrodynamicsResearch

Thermodynamics

Defi nition:

The theory of the relationship between heat and mechanical energy, and the conversion of one into the other. It deals especially with the interface between mechanical, chemical and electrical energy.

There are 4 recognised laws of thermodynamics, which hypothesize that: Energy can be exchanged betwen different physical systems as heat/ work.

* The zeroth law of thermodynamics: (underlies the defi nition of temperature.)If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

* The fi rst law of thermodynamics: (mandates conservation of energy, and states in particular that heat is a form of energy.)-Energy can neither be created nor destroyed. It can only change forms.-In any process, the total energy of the universe remains the same.-For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system.

* The second law of thermodynamics: the entropy of the universe always increases/perpetual motion machines are impossible.As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

* The third law of thermodynamics:concerns the entropy of an object at absolute zero temperature, and implies that it is impossible to cool a system all the way to exactly absolute zero.“ As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value. ”

Ilya Prigogine

Prigogine is known best due to his defi nition of dissipative structures and their role in thermodynamic systems far from equilibrium, a discovery that won him the Nobel Prize in Chemistry in 1977.

Fluid Dynamics

Defi nition:

The branch of fl uid mechanics dealing with fl uid (liquids and gases) in motion. It contains empirical and semi-empirical laws that are derived from fl ow measurement.

Aerodynamics: The study of air in motion, particulary when they interact with a moving object.

Hydrodynamics: The study of liquids in motion. Branches of hydrodynamics include hydraulics and pneumatics.

Natural occurences that obey the laws of fl uid dynamics:- Air in the lungs- Blood in the veins- Air and water currents

Applications of fl uid dynamics:- Calculating forces and movement on aircraft- Predicting weather patterns- Water fl ows in tanks, pipes and waterways- Creating three-dimensional (3D) models of tsunamis- Injection-fre epidermal drug delivery- Animating fl uids for movies and video games

FlowThere are a number of different types of fl uid fl ow, some being:- Laminar- Turbulent- Cavitation- Secondary

The understanding of fl ow offers potential for increased effi ciency of processing technologies.

Turbulent fl ow

Motion wherby a fl uid has local velocities and pressures that fl uctu-ate randomly. The overall fl ow is in one direction but the subcur-rents in the fl uid move in irregular patterns.

Natural occurence: Mixing warm and cold air over the atmosphere by wind( clear-air turbulence). Most of air circulation over landOcean currents- mixing warm and cold water

Examples: Smoke rising from a cigareteeExternal fl ow over vehicles (cars, airplanes, ships and submarines.

Laminar fl ow

Smooth’ fl ow in which particles of the fl uid move in parallel layers, each of constant velocity, with no disruption between the layers. It is the opposite of turbulent fl ow.

Example: Air fl owing over an aeroplane wing.

Example of laminar and turbulent fl ow:Smoke from a cigarette fl owing into the air. Smoke rises vertically and smoothly for some distance( laminar) then starts undulating into non-laminar( turbulent) fl ow.

Types of Flow

Secondary fl ow

This occurs in regions whereby the fl ow is signifi cantly diferent in speed and direction to that which is predicted for a fl uid (the pri-mary fl ow).

Natural occurence: dust devils/ tornadoes

Cavitational fl ow

The formation of vapor pockets/ bubbles in a fl owing liquid in areas of very low pressure. Can be caused by mechanical forces, such as the rotation of a ship’s propeller.Shock waves produces by inertial cavitation can cause signifi cant damage to machines, such as turbines and propellers. It also causes a lot of noise, vibration and loss of effi ciency.

Applications:- Homogenization (blending) of colloidal liquid compounds e.g.paint mixtures/ milk- Water purifi cation- Shock wave lithtripsy- to destroy kidney stones- Industrial cleaning

Natural occurence:Negative: It may also affect swimming animals.e.g dolphins and tuna. Cavita-tion bubbles on dolphin tail fi ns are painful, and force them to swim slower, while the swimming speed of tuna is limited by air fi lms formed around the fi ns due to cavitation.

Positive: Pistol shrimp: snaps a specialized claw to create cavitation, which can kill small fi shMantis shrimp: uses cavitation to stun, smash open or kill shellfi sh for food.

Turbulent fl ow:

Mixing of Saline water and Pure Water

Case study:Effects of waves on beaches

Wave Formation:The turbulent frictional action of wind over water causes wave for-mation.

Extreme Wave Effect: Hydroerosion

Natural Hydroerosion caused by wave action: 12 Apostles

Man- made Hydroerosion caused by hydraulic mining: Las Medulas, Spain & Mallakoff Diggins, California

Waves and Breaker Types

Break graudally over a considerable distance.Formed where there is a gently sloping bottom, it is the most commonly observed type of wave.

A wave break occurs when the waves slow down and steepen then ‘break’ and froth.

As water enters a depth that is shallower than half its wavelength, water near the bottom of the wave begins to touch the bottom. It is retarded by friction, causing the wave to increase in height unitil it’s too high for it’s motion and falls over into the preceding trough.

There are 3 types of breakers: -Spilling -Plunging -Surging

Curl over and break with a single crash. front is concave, rear convex.Formed where there is a moderately sloping bottom.

Peak up, but surge onto the beach without spillin or plunging. technically, they don’t ‘break’.Formed where the slope bottom so steep that the wave doesn’t break until it reaches the shoreline.

surging

spilling dissipative beach

intermediate beach

refl ective beach

The different breaker types lead to formation of different kinds of beaches, either building up or eroding away the sandy beach.

plunging

Beach formations from Different Breaker Types

Short period (plunging) waves, moderate slope

WAVE TANK EXPERIMENTS

The end result is an intermediate beach. Sediment is washed away from the beach, and deposited some dis-tance under-water, forming a berm.

Longer period waves, moderate slope - Surging breaks

The end result is a refl ective beach.Sediment is washed towards the shore, building up the beach.

lower gradient, short period - Spilling breaks

The end result is a stable beach.Sediment is washed away from the shore but is washed back, creating a sort of equilibrium.

Applications of Flow

Mercedes Benz Bionic Car

The Bionic Car takes the boxfi sh as its aerodynamic and structural precedent. Because the fs is outstandingly streamlined, it was taken as an example of an aerodynamic ideal. It has a very low drag coef-fi cint.

The optimised structure of the car is considered along the principles of bone formation, and apparently allows great rigidity with light weight.

Examples of buildings shaped/affected by fl ow

Wind shaped pavilion

The wind shaped pavilion is a design proposal for a large fabric structure that can be used as a public or private pavillion. As a lightweight fabric structure, the wind slowly and randomly rotates each of the six segments around a central open support frame. This continually alters the shape of the pavillion, while at the same time generating electrical power for its nighttime illumination.

Wind Veil Facade- Ned Kahn

In 2002, Ned Kahn worked with the staff of Technorama, the major science center in Switzerland, and their architects, Durig and Rami, to create a facade for the building which is composed of thousands of aluminum panels that move in the air currents and reveal the complex patterns of turbulence in the wind.

Differences from normal commercial aircraft:

- First commercial airliner to have a central wing box made of car-bon fi bre reinforced plastic.

- First to have a smoothly contoured wing cross section. The wings of other commercial airliners are partitioned span-wise into sec-tions. This fl owing, continuous cross section optimises aerodynamic effi ciency. Thermoplastics are used in the leading edges of the slats.

- The new material GLARE (GLAss-REinforced fi bre metal laminate) is used in the upper fuselage and on the stabilizers’ leading edges. This aluminium-glass-fi bre laminate is lighter and has better corro-sion and impact resistance than conventional aluminium alloys used in aviation. Unlike earlier composite materials, it can be repaired using conventional aluminium repair techniques.

- Newer weldable aluminium alloys are also used. This enables the widespread use of laser beam welding manufacturing techniques— eliminating rows of rivets and resulting in a lighter, stronger struc-ture.

Airbus A380