Paper 8
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40 questions
| 🇬🇧 | 🇬🇧 |
| 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 |
| 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 |
| Gross thrust, net trust | Net = m(Vj - V), gross = mVj |
| 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 |
| Gross thrust, net trust | Net = m(Vj - V), gross = mVj |
| 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 |
| 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 |
| How similar are plane emissions to other transport | Similar to car with 2 passengers, much higher than bus/train |
| 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 |
| 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 |