Question

1. Experimental aerodynamicists rely on accurate measurements of flow velocities. One method to optically measure velocity is particle image velocimetry (PIV). How does PIV work and what is needed for the technique?

2. On the north pole of Saturn, a hexagonal flow pattern exists. How do scientists explain this phenomenon?

3. Unfortunately, in ME 441 we do not have much time to focus on helicopter dynamics which have entirely different performance metrics than fixed wing aircraft. For example, helicopters can rely on autorotation upon engine failure. How does autorotation work?

4. Fluid dynamics of water, namely hydrodynamics, results in new physics not usually see in aerodynamics. One such phenomenon is cavitation which is an effect commonly seen with regards to ship propellers. What is cavitation and how does it affect propeller performance?

Answer 1

Ans 2 Few Scientists at Oxford University has explained the presence of hexagonal flow pattern .This is formed where presence of a steep Saturn's atmosphere. In the laboratory scientists has observed that when a circular t liquid rotated at different speeds at its centre and periphery. The most co sided, but shapes with three to eight sides we of turbulent flow between the two different rotating fluid bodies with dissimilar speed of stable vortices of similar size form on the slower (south) side of the fluid boundary and these interact with each other to space themselves out evenly around the perimeter. The pre the vortices influences the rise to the polygon effect. and viscosity parameter places, such as Saturn's South Pole or the poles of Jupiter. latitudinal gradient exists in speed of atmospheric winds in ank of mmon shape was six re also produced. The shapes form in an area s. A number sence of boundary to move northward where each is present and this gives Polygons do not form at wind boundaries unless the speed differential s are within certain margins and so are not present at other likely Ans 4 Cavitation is the formation and abrupt collapse of vapour-filled bubbles. This place at the surface of propeller where the pressure falls below the vapour pressure of the flow medium. The v evaporate. The vaporization itself does not cause the damage the damage hap vapor almost im increases.Once the bubble collapses a shock wave causes damage to the propeller by erosior or cavitation of surface process takes apour pressure of a liquid is the pressure at which the liquid begins to boil or mediately after evaporation collapses when velocity decreases and pressure So, cavitation affects the performance of propeler by damage to the propeller blade surfaces causing a severe loss of thrust and, eventually, physical damage to the surface of the propeller blades The effects of cavitation including loss of speed and damage to the propeller blades and incorrect pitch distribution along the length of the blade which reduces the efficiency of propeller.