Introduction. Work devided in four parts. 1. Vehicle construction. 2. Wind turbines. 3. Efficiency measuring

Transcription

1 Windcar

2 Problem Construct a car which is propelled solely by wind energy. The car should be able to drive straight into the wind. Determine the efficiency of your car.

3 Introduction Work devided in four parts. Vehicle construction 2. Wind turbines 3. Efficiency measuring 4. Determination of maximal working velocity

4 Vehicle construction. Gearbox ratio :2

5 Why is vehicle moving? The internal forces can not change momentum of system Observing of motion is reduced to determination of external forces Sole external forces are friction forces Without slipping we have : dω r = a dt With wind powered vehicle everything is the same

6 Wind turbines We have two types of wind turbines vertical and horizontal axis In our case advantageous are vertical axis wind turbines Vertical axis wind turbines Existing few types : Savonius, Dareius rotor and Cup Anemometer rotor Our research is based on Savonius and Cup anemometer rotor Dareius rotor desires pre-rotation

7 Cup Anemometer rotor Used in Anemometers Consists of four identical Half - spheres

8 Which forces cause torque? Force on a blade : F = 2 C x ρv 2 S ρ - Density v - Wind Velocity S C x - Blade Area - Drag coefficient V ρ M l F ρ 3 4 C x of blade. is 3 times greater then C x of blade 2. l Rotor is starting to rotate clockwise Torque equals to : M = lv 2 ρs( C x C ) 2 y ρ v S C C l x y - Density - Wind velocity - Blade area - Drag coefficient of - Drag coefficient of - Blade length 2 blade. blade 2. F ρ 2

9 Savonius Rotor Used in water pumps There is a stream between blades

10 Savonius Rotor It is uncommon Force configuration is the same sa Anemo There is stream between blades V ρ F 2 That stream increases efficiency at high angular velocities F There is drag force acting on a Rotor in wind stream D ρv 2 2 C S t ρ - Density v - Wind velocity S C t - Rotor cross section area - Drag coefficient of whole rotor

11 Efficiency determination

12 Determination of wind power Wind kinetic energy : E kv = 2 mv 2 = 2 ( 2 ρ Avt) v = ρatv 2 3 ρ - density v - Wind velocity A - Crosssectional area of blade t - Time Wind power : P v = de dt = ρ Av 2 3 ρ - Density v - Wind velocity A - Cross sectional area of blade

13 Wind power measurment V ρ h 0 m

14 Wind power measurment V ρ W = E mg( h ) p = h0 h m P a = dw dt = mg( h h0) t h 0

15 Efficiency determination Cup anemo 0,4 0,3 Rad [J] 0,2 0, 0, Vrijeme [s] dw P a = = 0, 08W P W dt v = 0, 35 η = C p = 0,33 = 3,3%

16 Efficiency determination Savonius 4m/s 0,30 0,25 0,20 Rad[J] 0,5 0,0 0,05 0, Vrijeme[s] dw = P a = = 0, 0043W η = C = 0,044 = 4.4% dt p P v 0, 096W

17 Efficiency determination Savonius 5m/s 0,30 0,25 0,20 Rad [V] 0,5 0,0 0,05 0, P a = W Vrijeme[s]

18 Power measurment Savonius 7m/s 0,7 0,6 0,5 0,4 Rad[J] 0,3 0,2 0, 0, Vrijeme[s]

19 Determination of maximal working velocity

20 Determination of maximal working velocity It is wind velocity at which the vehicle stops working Slipping Starts There are few methods of increasing maximal velocity : Vehicle mass increasing Adding downforce wings spoilers

21 Influence of vehicle mass to max. wind working velocity While vehicle is accelerating straight into the wind equation of motion is : dv m dt = F t F n = Me r F n M e - r - F n - Rotor Torque Gearbox Ratio Motor Wheels radius - Friction force on other wheels The condition for acceleration without slipping is : Me r µ F p F p - motor wheels pressure force µ - fricion cofficient on motor wheels

22 Wheels pressure force Without rotor drag Forces are : D Fp = Fp = m 2 g L h T L F p Drag force causes torque in point T Now pressure forces are : M D = Dh F p = mg + 2 hd L F p = 2 mg hd L

23 Max. Velocity as a function of vehicle parameters By inserting in slipping Condition and solving for v we have : v g = From equation follows : µ r( Lmg + 2hD) ellρsc x µ - motor wheels friction coefficient e - gearbox ratio r m - Vehicle mass S - Blade area ρ - Air density h - visina C - Motor wheels ratio x hvatišta turbine - blade drag coefficient L - distance between motor wheels and point T v = am + b

24 Experimental test of equation 3 2 Kriticna brzina vjetra [m/s] Masa vozila [g] Congruence is relatively good with respect to our simple Theoretical model

25 Influence of downforce wings on max. working velocity Wings increase pressure forces on wheels Wings also increases cross sectional area of whole vehicle Masa=50g Bez zakrilca Prednja zakrilca Stražnja zakrilca Sva zakrilca Gran.Brzina 8 m/s 7.7 m/s 8.5 m/s 9. m/s

26 Conclusion Vehicle powered solely by wind energy is constructed Research was made on Cup anemo and Savonius rotors Vehicle efficiency with Cup anemo is 3.3% Vehicle efficiency with Savonius rotor is 4.4% For savonius rotor eeeiciency is function of angular velocity Dependence of max. working velocity on vehicle parameters is determined Influence of downforce wings is lower then expected Maximal achived working velocity 2 m/s