The blades of a wind turbine are ready to be installed on a turbine on top of a ridge. The horizontal blades are supported at each end by saw horses, when a storm front arrives. The turbine crew huddles in their truck as the rain starts and the wind picks up, increasing eventually to 25 m/s. Realizing that the wind coming up the western slope of the ridge roughly follows the 10° slope, the field engineer performs a quick calculation and drives his truck upwind of the blades to disrupt the air flow around the blades, preventing them from being lifted by the wind and damaged. The blades are 5m long, 0.5m wide, and have a mass of 50 kg. The blades are approximately symmetric airfoils (the engineer remembered that potential flow theory predicts that, prior to stall, the lift coefficient of a symmetric airfoil is approximately C = 2n sina). Assume that the center of lift and drag force is concentrated over the center of mass of the blade and that the leading edge is facing into the direction of the wind. p = 1.2 kg/m³. (a) Was there a reason to be concerned? At what wind speed will the blades be lifted by the wind, assuming that there is no drag? (b) If they are lifted by a 25 m/s wind, how fast will they be accelerated horizontally if the blade's lift to drag ratio, C,/C, = 0.03? The operating conditions found at two different points of a blade on a wind turbine are shown. These conditions were determined at a temperature for which the kinematic viscosity is 1.33 x 10$m²/s. What are the Reynolds numbers found at each blade section? Wind velocity (m/s) Angle of attack (degrees) Location (r/R) Chord (m) 0.15 15 1.5 0.95 75 0.35 7.5

A 150-m-wide river flows due east at a uniform speed of 2.0 m/s. A boat with a speed of 6.0 m/s relative to the water leaves the south bank pointed in a direction 30° west of north. (a) Draw the vectors triangle using scale 1.0 cm : 1.0 m/s and label the corresponding relative velocities. (b) Determine the magnitude of the boat's velocity relative to the ground. (c) Determine the direction of the boat's velocity relative to the ground. (d) Find the time for the boat to cross the river. SS

7.60 PLUS The pump shown draws water (20°C) through a 20 cm suction pipe and discharges it through a 10 cm pipe in which the velocity is 3 m/s. The 10 cm pipe discharges horizontally into air at point C. To what height h above the water surface at A can the water be raised if 26 kW is delivered to the pump? Assume that the pump operates at 60% efficiency and that the head loss in the pipe between A and C is equal to 2 V/2g. Assume a = 1.0 throughout. Pump C Water PROBLEMS 7.59, 7.60

One part of an inspection system in a packaging operation uses an air blast to remove defective pieces of cardboard from the conveyor belt. The blast is initiated by a sensor and clocked so that the product is in front of the blast at just the right . The product is going to be dumped onto a shelf next to the conveyor belt. Determine the speed of the air jet required to tip the cardboard off the conveyor. The density of air is 1.10 kg/m3. The cardboard has a mass of 0.10 kg and the jet has a diameter of 10 mm.