Introduction to Wind Tunnel

The basic concept and operation of subsonic current of breeze burrow was demonstrated in this experiment by conducting surface sop up analytic thinking on a NACA 0015 business linefoil. The small subsonic turn on burrow along with apparatus such as, the manometer rake, the inclined manometer and the pitot static pipage were mathematical function with divergent baffle cut backtings to record varying rack readings. To achieve this objective, some assumptions were make for the lower identify of subsonic flow to simplify the overall analysis.From the obtained silky measurements u evilg a pitot-static pipe mounted ahead of the demeanorfoil at the turn out subdivision, the actual pep pill was determined and by relating it to the suppositious focal ratio, the upper coefficient was mensural. The speed coefficient varies for distributively baffle setting by a cipher of decimals, thus the velocity coefficient back tooth be used as a correction factor. Further, the co efficients of thread were calculate for the following burthens of attack, 10o, 15o, and 20o and were compared with the published values. INTRODUCTIONThe annul cut into is an absolute necessity to the development of modern aircrafts, as today, no shaper delivers the final product, which in this case drop be civilian aircrafts, troops aircrafts, missiles, spacecraft, and automobiles without measuring its lift and sop up properties and its stability and controllability in a interlace burrow. Benjamin Robins (1707-1751), an English mathematician, who first employed a whirling strengthen to his machine, which had 4 feet long arms and it, spun by falling weight playacting on a pulley however, the arm tip reached velocities of only hardly a(prenominal) feet per second. 4 Figure 1 Forces exerted on the airfoil by the flow of air and opposing reaction on the control volume, by Newtons third practice of law. 1 This experiment volition determine drop behind kings experienced b y a NACA 0015 airfoil, subjected to a constant entry velocity at miscellaneous baffle settings with varying lists of attack.DATA ANALYSIS, THEORATICAL BACKGROUND AND PROCEDURE Apparatus in this experiment as shown in the figure 2, consisted of a small subsonic wind tunnel. The wind tunnel had an penetration cross-section of 2304 in2 and an spillage crosses section of 324 in2. A large compressor surprised air from room) into the inlet through the outlet tunnel and back into the room. This creates a steady flow of air and a coitus high velocity put up be achieved in the test section. instrumentality on the wind tunnel consisted of an inclined manometer and a pitot-static tube in the test section also a manometer rake piece of ass the tried and true objet (airfoil NACA 0015). The manometer rake consisted of 36 inclined manometers telephone number 36 is used as a reference for the static haul. All other manometer measures the pressure behind the object in the airflow. Figu re 2 tress tunnel set up with instrumentation 5Before the experiment was performed the laboratory conditions were recorded, the room temperature was measured to be 22. 5 C (295. 65) and the atmospheric pressure 29. 49 inHg (99853. 14Pa). Theory The setup of this experiment includes a NACA 0015 airfoil placed in the wind tunnel. Considering the cross-sectional area A1, velocity V1, and the density of air p1 at the inlet and besides the cross-sectional area A2, velocity V2, and the density of air p2 at the outlet and by assuming that no mass is lost between the inlet-outlet section, we desexualise the mass conservation equation, p1 V1 A1 = p2 V2 A2 (1).Further, the airflow whoremaster be assumed to be incompressible for this experiment due to low velocity, the equation (1) can be reduced to V1 A1 = V2 A2 (2), muchover, the air is assumed to be inviscid, the Bernoullis equation, p1+12? V12=p2+12? V22 (3) and the equation (2) can be reduced to Vth=2(p1-p2)/? 1-A2A12 (4) in order to ensure the suppositious velocity. The pitot static tube is used to calculate the actual velocity of the flow by use, Vact= 2(p2-p1)? (5). Furthermore, the velocity coefficient can be calculated using, Cv=VactVth (6).The pressure and shear stress acting on the NACA 0015 airfoil produces a resultant delineate R, which according to the Newtons third law produces an equal and opposite reaction force. For this experiment, in the condition of lower range of subsonic velocity, it can be assumed that pressure and density will be constant over the airfoil thus, D=jj+1? (uo2-ui2)dy=-12? uj2+uj+12o-uj2+uj+12iyj+1-yj (7) can be used to calculate the drag and, CD=Drag12(? air*Velocity2*area) (8) can be used for calculating the coefficient of drag. Procedure Part 1, Variation of inlet cross sectionIn this first musical composition we recorded the pressure behavior in the test section by decreasing the inlet area. After the safety instructions were go pastn by the TA and a chart for the readings prepared on the white board the wind tunnel was sullen on. Two students were taking readings simultaneously from the inclined manometer in the test section and the static pitot tube, the readings were recorded in dining table 1. Between each reading the compressor was turned off due to the sound level, it was important to give the compressor some time after each start up to strike the same conditions as in the previous measurement.Part 2, recording the wake visibility of NACA 0015 For this cut off of the experiment the inlet area was fully opened and the airfoil first set to an angle of attack of 10, the wind tunnel was turned on and all 36 readings recorded (table 2) from the manometer rake. The measurement was repeated for an angle of attack of 15 and 20. RESULTS AND DISCUSSION The linear relationship between the V actual and the V theoretical approves of the theory that the velocity coefficient, Cv can be used as a correction factor for the theoretical velocity. This is further demonstrated in (Graph2). The calculated results are shown in table 1.The approximated publications values of the coefficient of drag for NACA 0015 airfoil were obtained from a NASA published subject area 3 for the 10o AoA, the percent relative phantasm is 3. 1%, for 15o AoA, the percent relative error is 31. 0%, and for the 20o AoA, the percent relative error is 38. 7%. Increases in angle of attack lead to a more disturbed airflow behind the wing section. This disturbed airflow created more drag, these drag forces were clearly plain in table 3, 4. The angle of attack can be change magnitude until the quantity drag forces become larger than the resultant lift- force a wing is then no longstanding effective and stalls.The calculated drag forces are shown in tables 2-4. According to NASA, in their published report of energetic flow control at low Reynolds numbers on a NACA 0015 airfoil, its is suggested that, by positioning the wake rake around 4. 5 multiplication chord length behind wing to survey the wake. Further, two pressure orifices on opposite tunnel walls, aligned with the wake rake can be used to determine the average wake static pressure. This event of wake rake enables the wake to be surveyed with only a fewer moves of the wake rake, hence improving the measurements of drag using wake rake. 2 At large angles of attack, the upstream velocity of the airfoil can no longer be considered as the free-stream velocity, largely due to the miniature size of the wind tunnel relative to the NACA 0015 airfoil hence, the assumption that the uo max > ui is valid for this experiment.CONCLUSION Ergo, it is plainly seen in the graphs 1 and 2 that, the averaged velocity coefficient, Cv, 1. 063 can be used as the correction factor for the theoretical velocity. Further, the accurate (4-32) drag forces were calculated to be 2. 72 N, 13. 46 N, and 46. 4 N for the following angles of attack, 10o, 15o, and 20o. Moreover, the drag coefficient were also calculated based on the observed data and than were instantaneously compared with the lit values. For the 10o of angle of attack, the percent relative error was very(prenominal) nominal at 3. 1% however the drag coefficients for the 150 and the 20o were not very accurate, with the percent relative error of 31. 0% and 38. 7% respectively. This can be improved by implementing a smaller airfoil, so that the proportion of the wind tunnel covered by the airfoil is significantly smaller.Also, the skin clangoring losses along the edges of the wind tunnel may very well be taken into the account to achieve greater accuracy. Finally, it can be concluded that, as the angle of attack of the airfoil increases, the drag force will also increase due to the effect of flow separation. REFERENCES 1 Walsh, P. , Karpynczyk, J. , AER 504 aerodynamics Laboratory Manual De referencement of Aerospace Engineering, 2011 2 Hannon, J. (n. d. ). Active flow control at low reynolds numbers on a naca 0015 a irfoil. Retrieved from http//ntrs. nasa. gov/archive/nasa/casi. ntrs. nasa. gov/20080033674_2008033642. pdf 3 Klimas, P.C. (1981, March). Aerodynamic characteristics of cardinal symmetrical airfoil section through 180-degree angle of attack for use in aerodynamic analysis of vertical axis wind turbines. Retrieved from http//prod. sandia. gov/techlib/access-control. cgi/1980/802114. pdf 4 Baals, D. D. (1981). Wind tunnels of nasa. (1st ed. , pp. 9-88). National Aeronautics And Space Administration. 5Fig. 1, Wind tunnel set up with instrumentation, created by authors, 2012 APPENDIX Sample Calculations Note AoA = ANGLE OF ATTACK. Sample calculations part 1, Baffle opening 5/5 Conversion inH2O to Pa (N/m2) 1 inH2O=248. 2 Pa (at 1atm) ?2inH2O ? 248. 82 PainH2O=497. 64 Pa Theoretical velocity Equation (4) Vth=2(p1-p2)/? 1-A2A12 , where p1-p2=497. 64 Pa, A2=2304 in2, A1=324 in2, ? Density air (ideal gas law) laboratory conditions 22. 5 C (295. 65K), 29. 49 inHg (99853. 14Pa) ? =pRT=99853. 14Pa287JkgK(295. 65K)? 1. 1768 kgm3 ?Vth=2(497. 64pa)/1. 1768kgm31-2304 in2324 in22=29. 37m/s Actual velocity Equation (5)Vact= 2(p2-p1)? where p1-p2=522. 52 Pa, ? =1. 1768 kgm3 ? Vact= 2(522. 52Pa)1. 1768 kgm3=29. 80 m/s Velocity coefficient Equation (6) Cv=VactVth=29. 8029. 37=1. 015 Sample Calculations Part 2, Angle of attack 10o, tube 1For dL, tube number 36 served as a reference pressure for all readings 26. 4cm 9. 2cm = 17. 2cm or 0. 172m Pressure fight, equation (7) ?p=SG*? H2O*g*L*sin? =1*1000kgm3*9. 81ms2*0. 172m*sin20o=577. 06 Pa Velocity, equation (8) note pressure difference antecedently calculated V1=2*SG*? H2O*g*L*sin air=2*577. 06 Pa1. 1768kgm3=31. 32 m/s Drag force, equation (9), for ui a velocity away from the tunnel wall was chosen to achieve a more realistic drag force D=jj+1? (uo2-ui2)dy=-12? uj2+uj+12o-uj2+uj+12iyj+1-yj=-121. 1768kgm3(31. 32ms)2+( 31. 5ms)2o-2(31. 5m/s)2i0. 01m=0. 07 N Total drag force, summation lead toDtotal = 9. 04 N, however due to the v erge layer along the inner walls of the wind tunnel a more accurate summation is the sum of the values of tubes 4-32 which results in a total drag force of 2. 72 N. Coefficient of Drag Equation (9), for the drag force the more accurate summation of tube 4-32 was used CD=Drag12(? air*Velocity2*area)=2. 72N12(1. 1768kgm3*31. 50ms2*(0. 1524m*1. 00m)=0. 031 To compare the Cd to a value found in literature the Reynolds number is required Re=? air*V*cViscosity=1. 1768kgm3*31. 50 m/s*0. 1524m1. 789*10-5kgs*m=315782. 35 Observation and Results for Part 1Table 1, Observations/Results part 1 Baffle Opening Inclined Manometer (inH2O) Pa ( x 248. 82 Pa/inH2O) Pitot Static (inH2O) Pa ( x 248. 82 Pa/inH2O) V theoretical (m/s) V actual (m/s) Cv 55 2. 00 497. 640 2. 10 522. 52 29. 37 29. 80 1. 015 45 1. 80 447. 876 1. 90 472. 75 27. 87 28. 35 1. 017 35 1. 15 286. 143 1. 25 311. 02 22. 27 22. 99 1. 032 25 0. 45 111. 969 0. 46 114. 46 13. 93 13. 95 1. 001 15 0. 05 12. 441 0. 08 19. 905 4. 64 5. 82 1. 252 Table 1 The theoretical velocity was calculated using the eq. (4) and the actual velocity was calculated using the eq. 5) from the obtained pressure data from the hand held pitot tube. The velocity coefficient, Cv, was calculated using the eq. (6). Note The sample calculations are given in the appendix section of this report. Graph 1 The results from Table 1 were used to create the while of V actual Vs. V theoretical. Graph 2 The plot of the velocity coefficient and the actual velocity. From the plot, it can be clearly seen the very minute difference between the velocity coefficient values. Observation and Results for Part 2 Table 2, Observations/Recordings part 2, Angle of attack 10 swimming length in tube (. 1cm), Inclination 20Tube Nr. L (cm) dL (cm) Pressure (Pa) u (m/s) Drag force (N) 1 9. 2 0. 07 0. 07 0. 07 0. 07 2 9. 0 0. 00 0. 00 0. 00 0. 00 3 9. 0 0. 00 0. 00 0. 00 0. 00 4 9. 0 -0. 07 -0. 07 -0. 07 -0. 07 5 8. 8 -0. 13 -0. 13 -0. 13 -0. 13 6 8. 8 -0. 13 -0. 13 -0. 13 -0. 13 7 8. 8 -0. 07 -0. 07 -0. 07 -0. 07 8 9. 0 0. 00 0. 00 0. 00 0. 00 9 9. 0 0. 00 0. 00 0. 00 0. 00 10 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 11 8. 9 -0. 03 -0. 03 -0. 03 -0. 03 12 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 13 8. 9 -0. 07 -0. 07 -0. 07 -0. 07 14 8. 9 0. 64 0. 64 0. 64 0. 64 5 11. 0 1. 68 1. 68 1. 68 1. 68 16 12. 0 1. 01 1. 01 1. 01 1. 01 17 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 18 8. 9 -0. 03 -0. 03 -0. 03 -0. 03 19 9. 0 0. 00 0. 00 0. 00 0. 00 20 9. 0 0. 00 0. 00 0. 00 0. 00 21 9. 0 -0. 03 -0. 03 -0. 03 -0. 03 22 8. 9 -0. 07 -0. 07 -0. 07 -0. 07 23 8. 9 -0. 07 -0. 07 -0. 07 -0. 07 24 8. 9 -0. 10 -0. 10 -0. 10 -0. 10 25 8. 8 -0. 10 -0. 10 -0. 10 -0. 10 26 8. 9 -0. 03 -0. 03 -0. 03 -0. 03 27 9. 0 0. 00 0. 00 0. 00 0. 00 28 9. 0 0. 00 0. 00 0. 00 0. 00 29 9. 0 0. 00 0. 00 0. 00 0. 00 30 9. 0 0. 00 0. 00 0. 0 0. 00 31 9. 0 0. 07 0. 07 0. 07 0. 07 32 9. 2 0. 34 0. 34 0. 34 0. 34 33 9. 8 0. 34 0. 34 0. 34 0. 34 34 9. 2 0. 07 0. 07 0. 07 0. 07 35 9. 0 5. 84 5. 84 5. 84 5. 84 36 26. 4 0 Reference 0. 00 0. 00 Total drag force (1-35) 9. 04 Total drag force (4-32) 2. 72 Coefficient of drag calculated 0. 031 Coefficient of drag literature 0. 030 Table 3, Observations/Recordings part 2, Angle of attack 15 Fluid length in tube (. 1cm), Inclination 20 Tube Nr. L (cm) dL (cm) Pressure (Pa) u (m/s) Drag force (N) 1 8. 2 0. 06 0. 06 0. 06 0. 06 2 8 -0. 01 -0. 01 -0. 1 -0. 01 3 8 -0. 01 -0. 01 -0. 01 -0. 01 4 8 -0. 04 -0. 04 -0. 04 -0. 04 5 7. 9 -0. 08 -0. 08 -0. 08 -0. 08 6 7. 9 -0. 04 -0. 04 -0. 04 -0. 04 7 8 -0. 01 -0. 01 -0. 01 -0. 01 8 8 -0. 01 -0. 01 -0. 01 -0. 01 9 8 0. 19 0. 19 0. 19 0. 19 10 8. 6 0. 49 0. 49 0. 49 0. 49 11 8. 9 0. 49 0. 49 0. 49 0. 49 12 8. 6 0. 39 0. 39 0. 39 0. 39 13 8. 6 0. 56 0. 56 0. 56 0. 56 14 9. 1 1. 40 1. 40 1. 40 1. 40 15 11. 1 2. 51 2. 51 2. 51 2. 51 16 12. 4 2. 74 2. 74 2. 74 2. 74 17 11. 8 2. 40 2. 40 2. 40 2. 40 18 11. 4 2. 00 2. 00 2. 00 2. 00 9 10. 6 1. 47 1. 47 1. 47 1. 47 20 9. 8 1. 06 1. 06 1. 06 1. 06 21 9. 4 0. 79 0. 79 0. 79 0. 79 22 9 0. 63 0. 63 0. 63 0. 63 23 8. 9 0. 49 0. 49 0. 49 0. 49 24 8. 6 0. 39 0. 39 0. 39 0. 39 25 8. 6 0. 32 0. 32 0. 32 0. 32 26 8. 4 0. 26 0. 26 0. 26 0. 26 27 8. 4 0. 26 0. 26 0. 26 0. 26 28 8. 4 0. 26 0. 26 0. 26 0. 26 29 8. 4 0. 26 0. 26 0. 26 0. 26 30 8. 4 0. 26 0. 26 0. 26 0. 26 31 8. 4 0. 26 0. 26 0. 26 0. 26 32 8. 4 0. 32 0. 32 0. 32 0. 32 33 8. 6 0. 56 0. 56 0. 56 0. 56 34 9. 1 0. 56 0. 56 0. 56 0. 56 35 8. 6 6. 30 6. 0 6. 30 6. 30 36 26. 2 0. 00 Reference 0. 00 0. 00 Total drag force (1-35) 19. 55 Total drag force (4-32) 13. 46 Coefficient of drag calculated 0. 145 Coefficient of drag literature 0. 100 Table 4, Observations/Recordings part 2, Angle of attack 20 Fluid length in tube (. 1cm), Inclination 20 Tube Nr. L (cm) dL (cm) Pressure (Pa) u (m/s) Drag force (N) 1 8 0. 16 0. 16 0. 16 0. 16 2 7. 6 0. 03 0. 03 0. 03 0. 03 3 7. 6 0. 03 0. 03 0. 03 0. 03 4 7. 6 0. 03 0. 03 0. 03 0. 03 5 7. 6 0. 03 0. 03 0. 03 0. 03 6 7. 6 0. 03 0. 03 0. 03 0. 03 7 7. 6 0. 03 0. 3 0. 03 0. 03 8 7. 6 0. 09 0. 09 0. 09 0. 09 9 7. 8 0. 16 0. 16 0. 16 0. 16 10 7. 8 0. 23 0. 23 0. 23 0. 23 11 8 0. 50 0. 50 0. 50 0. 50 12 8. 6 1. 17 1. 17 1. 17 1. 17 13 10 2. 37 2. 37 2. 37 2. 37 14 12. 2 3. 58 3. 58 3. 58 3. 58 15 13. 6 5. 39 5. 39 5. 39 5. 39 16 17. 6 7. 21 7. 21 7. 21 7. 21 17 19 7. 88 7. 88 7. 88 7. 88 18 19. 6 7. 88 7. 88 7. 88 7. 88 19 19 7. 04 7. 04 7. 04 7. 04 20 17. 1 5. 73 5. 73 5. 73 5. 73 21 15. 1 4. 09 4. 09 4. 09 4. 09 22 12. 2 2. 44 2. 44 2. 44 2. 44 23 10. 2 1. 37 1. 37 1. 37 1. 37 4 9 0. 66 0. 66 0. 66 0. 66 25 8. 1 0. 29 0. 29 0. 29 0. 29 26 7. 9 0. 23 0. 23 0. 23 0. 23 27 7. 9 0. 23 0. 23 0. 23 0. 23 28 7. 9 0. 19 0. 19 0. 19 0. 19 29 7. 8 0. 19 0. 19 0. 19 0. 19 30 7. 9 0. 19 0. 19 0. 19 0. 19 31 7. 8 0. 19 0. 19 0. 19 0. 19 32 7. 9 0. 46 0. 46 0. 46 0. 46 33 8. 6 0. 50 0. 50 0. 50 0. 50 34 8 0. 29 0. 29 0. 29 0. 29 35 8 6. 40 6. 40 6. 40 6. 40 36 26. 2 0 0. 00 0. 00 0. 00 Total drag force (1-35) 51. 30 Total drag force (4-32) 46. 64 Coefficient o f drag calculated 0. 489 Coefficient of drag literature 0. three hundred