Flow and Hydrodynamics Research
Thermodynamics Definition: 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 definition of temperature.) If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. * The first 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 definition 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 Definition: The branch of fluid mechanics dealing with fluid (liquids and gases) in motion. It contains empirical and semi-empirical laws that are derived from flow 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 fluid dynamics: - Air in the lungs - Blood in the veins - Air and water currents Applications of fluid dynamics: - Calculating forces and movement on aircraft - Predicting weather patterns - Water flows in tanks, pipes and waterways - Creating three-dimensional (3D) models of tsunamis - Injection-fre epidermal drug delivery - Animating fluids for movies and video games
Flow There are a number of different types of fluid flow, some being: - Laminar - Turbulent - Cavitation - Secondary The understanding of flow offers potential for increased efficiency of processing technologies.
Types of Flow Laminar flow Smooth’ flow in which particles of the fluid move in parallel layers, each of constant velocity, with no disruption between the layers. It is the opposite of turbulent flow. Example: Air flowing over an aeroplane wing. Example of laminar and turbulent flow: Smoke from a cigarette flowing into the air. Smoke rises vertically and smoothly for some distance( laminar) then starts undulating into non-laminar( turbulent) flow.
Turbulent flow Motion wherby a fluid has local velocities and pressures that fluctuate randomly. The overall flow is in one direction but the subcurrents in the fluid move in irregular patterns. Natural occurence: Mixing warm and cold air over the atmosphere by wind( clear-air turbulence). Most of air circulation over land Ocean currents- mixing warm and cold water Examples: Smoke rising from a cigaretee External flow over vehicles (cars, airplanes, ships and submarines.
Cavitational flow The formation of vapor pockets/ bubbles in a flowing 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 significant damage to machines, such as turbines and propellers. It also causes a lot of noise, vibration and loss of efficiency. Applications: - Homogenization (blending) of colloidal liquid compounds e.g.paint mixtures/ milk - Water purification - Shock wave lithtripsy- to destroy kidney stones - Industrial cleaning Natural occurence: Negative: It may also affect swimming animals.e.g dolphins and tuna. Cavitation bubbles on dolphin tail fins are painful, and force them to swim slower, while the swimming speed of tuna is limited by air films formed around the fins due to cavitation. Positive: Pistol shrimp: snaps a specialized claw to create cavitation, which can kill small fish Mantis shrimp: uses cavitation to stun, smash open or kill shellfish for food.
Secondary flow This occurs in regions whereby the flow is significantly diferent in speed and direction to that which is predicted for a fluid (the primary flow). Natural occurence: dust devils/ tornadoes
Turbulent flow: 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 formation.
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 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
Break graudally over a considerable distance. Formed where there is a gently sloping bottom, it is the most commonly observed type of wave.
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.
Beach formations from Different Breaker Types The different breaker types lead to formation of different kinds of beaches, either building up or eroding away the sandy beach. spilling
dissipative beach
plunging
intermediate beach
surging
reflective beach
WAVE TANK EXPERIMENTS Short period (plunging) waves, moderate slope
The end result is an intermediate beach. Sediment is washed away from the beach, and deposited some distance under-water, forming a berm.
Longer period waves, moderate slope - Surging breaks
The end result is a reflective 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 boxfish 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 coefficint. 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 flow 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.
Airbus A380
Differences from normal commercial aircraft: - First commercial airliner to have a central wing box made of carbon fibre reinforced plastic. - First to have a smoothly contoured wing cross section. The wings of other commercial airliners are partitioned span-wise into sections. This flowing, continuous cross section optimises aerodynamic efficiency. Thermoplastics are used in the leading edges of the slats. - The new material GLARE (GLAss-REinforced fibre metal laminate) is used in the upper fuselage and on the stabilizers’ leading edges. This aluminium-glass-fibre laminate is lighter and has better corrosion 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 structure.