| what to use for mass flow questions | m root(cp To)/A po |
| what to use for mass flow questions | m root(cp To)/A po |
| what to use for mass flow questions | m root(cp To)/A po |
| what to use for mass flow questions | m root(cp To)/A po |
| Epicycle gearbox | advantages
compact
light
cheap
disadvantages:
difficult to dissipate heat
difficult to use helical gears -> noisy, load sharing |
| overall efficiency | = n_p x n_th = work to aircraft / energy released in combustion.
= thrust/mf x speed/LCV = 1/sfc x V/LCV |
| Gross thrust, net trust | net = m(Vj - V), gross = mVj |
| What is phi? | Flow angle, angle from rel velocity to plane of rotation
? = ? + ? |
| What is theta? | Blade twist |
| what is velocity far upstream, at the blade, far downstream? | V, V(1-a), V(1-2a) |
| What is a', and therefore what is incoming tangential air speed viewed from blade reference frame | a' is tangential induction factor - the proportion of air that is deflected sideways into the plane of rotation.
Therefore incoming tangential airspeed = ?r(1 + a') |
| lift and drag are defined relative to what | relative to incoming flow ?, NOT the blade twist. |
| tip speed ratio | ? = ?r/v
where v = wind speed |
| Triple bottom line | Financial Performance
Environmental Performance
Social Performance |
| Why is shell made of multi-directional | easy to mould, tear resistant (impacts), carries bending, shear and normal stresses |
| Why is spar made of uni-directional | predominantly bending stress in one direction |
| why is tower sometimes steel | tower mass not as important, cheap, easy to form into circle by rolling sheets. |
| equivalent tower mass if all at top | 2m + 0.24 x 2m |
| work coefficient | = |
| Flow coefficient | = |
| Area of compressor/turbine stage | 4pi r_mΔR |
| Why is it better to have more than minimum turbine stages | Cooling limits loading due to cooling flows limiting boundary layer development |
| Gross thrust, net trust | net = m(Vj - V), gross = mVj |
| root(gamma R / cp)? | = |
| how similar are plane emissions to other transport | similar to car with 2 passengers, much higher than bus/train |
| power vs wind speed graph | is |
| how to calculate core exhaust velocity of jet | use pressure at turbine exit and pressure of atmosphere to calculate temperature drop using isentropic equations. Then use delta h = 1/2 V^2 |
| typical work coefficient for turbine | =2 for around 90% |
| propulsive efficiency | 2V / (V + Vj) derived from power to aircraft/power to jet |
| thermal efficiency | delta KE / mf LCV derived from kinetic energy added to air/energy released in combustion |
| overall efficiency | = n_p x n_th = work to aircraft / energy released in combustion.
= thrust/mf x speed/LCV = 1/sfc x V/LCV |
| what are graphs for axial and tangential velocity along the path of the air. What is the axial velocity downstream? | 2wra' upstream |
| assumptions for BEM to calculate forces on blades | constant section thickness -> c(r), r, v0, w |
| BEM steps for a, a', flow angle, forces | choose a = a' = 0
calculate flow angle
calculate cL, cD, cN, cT
calculate a, a' required for cN, cT
if different -> go back to step 2
if not -> calculate forces on blades |
| sigma = rotor solidity = what? | amount of the circumference of the rotor plane the blades take up
=cB/(2pi*r) where B is number of blades |
| Doubly fed induction generator schematic | is |
| advantages of doubly fed induction generator | can generate reactive power
allows variable speed operation
only requires fractionally rated power convertor
-> works by simulating rotor resistance with artificial source, thereby changing value of slip that gives max torque. Avoids losses in those resistors |
| Epicycle gearbox | advantages
compact
light
cheap
disadvantages:
difficult to dissipate heat
difficult to use helical gears -> noisy, load sharing |
| sync generators vs induction | Sync:
needs more powerful convertor to handle conversion from full rated power to sync speed of turbine. Heavier, extra cost. No gearbox however |
| what to use for mass flow questions | m root(cp To)/A po |
