ME 241-S ’11 Final Report(04/27/2011) Preprint typeset using LATEX style emulateapj v. 11/10/09 Studying Near-Surface Effects of the Dyson Air-Multiplier Airfoil Team 12:Michael Hua 1 , Dev Ashish Khaitan 2 , Paul Kintner 1 ME 241-S ’11 Final Report(04/27/2011) ABSTRACT We have studied the phenomena on which the Dyson Air-Multiplier (hereafter fan) is based. In this study, we have identified that the primary component that allows the fan to work is the unique design of its airfoil. We discuss our experimental design and results of a near-surface analysis of a two-dimensional cross section of the airfoil. Fiberglass was used to mold the airfoil within a foam exoskeleton. A null displacement manometer was used to measure the airflow velocities at the boundary layer and a high-speed camera was used to observe the flow. Subject headings: Dyson Air Multiplier, Wind Tunnel, Venturi Effect, Coanda Effect, Fiberglass Molding, Null Displacement Manometer, Anemometry 1. INTRODUCTION A wind tunnel is a research tool used in aerodynamic research. It is used to study the effects of air moving past solid objects. Air is blown through a duct equipped with a viewing port and instrumentation where models or geometrical shapes are mounted for study. Typically the air is moved through the tunnel using a series of fans. For larger wind tunnels several meters in diameter, a single large fan is not practical, and so instead multiple fans are used in parallel to provide sufficient airflow, such as in the 30-by 60-Foot Tunnel at NASA’s Langley Research Center. The airflow created by the fans entering the tunnel is itself highly turbulent due to the fan blade’s motion. The air moving through the tunnel needs to be relatively turbulence-free and laminar (1). To correct this problem, closely spaced vertical and horizontal air vanes are used to smooth out the turbulent airflow before reaching the subject of the testing thus increasing the overall length of the tunnel. This design is less than ideal for a wind tunnel but it is still the prevalent design. 1 Dept. of Mechanical Engineering, University of Rochester, Rochester, NY 14627 2 Dept. of Physics and Astronomy, University of Rochester, Rochester, NY 14627 Fig. 1.— Dyson Air-Multiplier AM01(6) Dyson Ltd claims that their product, the Dyson Air Multiplier (Figure 1), efficiently creates laminar airflow with no buffeting or uneven airflow, a characteristic that a wind tunnels settling chamber seeks to reduce. This elimination of buffeting and the creation of steady laminar flow is of great interest to designers of the wind tunnel, particularly, the possibility of placing the test target closer to the source of flow (Figure 2). Dyson Ltd’s results from laser Doppler anemometry show that there are two regions close to the source of flow that offer steady laminar flow (2). One region of opportunity to test a target is right in the middle of the source and the other 2 Fig. 2.— The smoothness of the resulting airflow was tested and proved using an optical technique called Laser Doppler Anemometry. Millions of tiny particles projected by the fan reflect thousands of readings a second, plotting air speed and direction. (2) Fig. 3.— A cross sectional view of the Dyson Air-Multipliers airfoil with the theoretical streamlines superposed outside the airfoil. (7) Fig. 4.— A side view of the Dyson airfoil to be constructed. The dimensions are 4.0” x 0.5” for the cross section. There is a small groove visible between the top and bottom of the air foil along with the notch present on the lower airfoil Fig. 5.— An angular view of the Dyson airfoil to be constructed. The dimensions are 7.0” x 4.0”x 0.5’ for the cross section. The groove for air flow is faintly visible. chord length made out of fiberglass. The air was supplied from a compressed air source. Testing for steady state region lies 20 inches downstream. There is no publicly available record of this study. Due to time restrictions with the project we were only be able to look at the near surface effects of the airfoil. We have outlined a method to test the feasibility of this design for a wind tunnel by analyzing the laminar region around the source. The process of building and flow was performed with a null displacement manometer. Once a steady state flow was detected the manometer was used to measure airflow properties around the boundary layer. The manometer probe has a small diameter so while it may be able to measure velocities along the boundary layer, but it does not have resolution to detect the boundary layer close to the slit. constructing a full-scale version of a Dyson Air Multiplier inspired wind tunnel without understanding the under- 2. THEORY lying processes is not cost effective. We believe that the Dyson’s patent states that the Air Multiplier makes unique airfoil design is the secret to the Dyson Air Mul- use of a Coanda surface in order to exploit the Coanda tiplier. Further experiments may be performed to eval- effect (3). This effect is well documented and used in uate other characteristics of the Dyson Air Multiplier to several industrial and commercial applications, including produce an ideal wind tunnel. Here a method for the the increase in lift for low-speed flying in aircraft (4). construction and testing of our airfoil is outlined. According to Henri Coanda, this effect is achieved by A two-dimensional cross section of their circular de- a combination of sufficient fluid velocity flowing out of sign is used for our implementation. The cross section a suitable orifice, resulting in entrainment of the sur- was be extruded to construct an airfoil with a constant rounding fluid. To elaborate, Coanda observed that high Dyson Airfoil 3 4, as the air exits the airfoil, it is funneled through a small slit (7). The fluid velocity greatly increases with this reduction in area, resulting in optimal entrainment of air. Dyson also claims that air is drawn in from behind, or induced, and this can be explained by Bernoulli’s principle. As the air leaves the fan at a higher velocity than the air behind the fan, it creates an area of low pressure. This pressure differential between the high velocity air and still air behind is what draws in the induced air. This combination of entrainment from the Coanda effect Fig. 6.— A lengthwise view of the foam mold used to construct the two halfs of the airfoil. and inducement by Bernoulli’s principle is what makes the Air Multiplier’s airflow 15 times its air intake (3). velocity flowing out of a small area draws in additional Coanda states that the exact degree of bending can flow from surrounding fluid when the jet of fluid enters be adjusted for optimized entrainment according to the another large volume of fluid. Also, if a Coanda sur- fluid’s characteristics, as mentioned earlier. According to face, one that curves away from said orifice, is present, Dyson’s patent, their inventors have found the optimal the fluid flow will tend towards the surface, hugging it Coanda surface profile for entrainment of air, one with and bending away from the outlet (5). This effect of en- an airfoil cross section with a 16◦ angle between the top trainment and bending of flow varies in degree by several and bottom surfaces and whose cord length is a constant factors, including the orifice size, fluid velocity and fluid at approximately 1.5”. properties like viscosity and density. An exact quan3. EXPERIMENTAL SETUP titative measure of entrainment and bending have not been documented outside of Dyson’s claims of 15-times We constructed an airfoil that achieved airflow similar volumetric-flow-multiplication. Though Dyson uses this to that of the Dyson Air Multiplier. An air compres- explanation in their patent, there is more to the air mul- sor was used to produce an airflow through the foil in tiplication. a manner similar to the Dyson fan. The air flowed into Dyson’s fan multiplies airflow in several steps which our airfoil on both sides A null displacement manometer can all be explained by the Coanda Effect, the Venturi was used to measure flow velocity near the surface of our Effect, and Bernoulli’s principle. First, air supplied at airfoil. the base of the fan is drawn in by an impeller (6),(3). The airfoil has dimensions of 7.0” x 4.0”x 0.5” as seen This creates high pressure in the hollow ring of the fan, in Figure 5. The 16◦ angle along the horizontal surface which is the cross section of an airfoil (Figure 3). By and the Coanda surface and the top section of the airfoil propelling air out of a 1.3 mm slit located on the inside of which was used by Dyson was recreated in our airfoil. its ring, air flows across one side of the airfoil, the Coanda The slit in the airfoil is 1.3 mm (0.0512”); according to surface. This results in entrainment of surrounding air, Dyson this can range from 1 mm to 5 mm (0.0394” to just downstream of the airfoil. The Venturi Effect is a 0.197”) (3). The construction of the airfoil was done factor in creating the optimal air velocity, resulting in by using fiberglass and a foam exoskeleton as can be the Coanda Effect. As seen in the cross section of Figure seen in Figure 6. The foam mold was acquired from 4 ments for the top and bottom pieces as seen in Figure 4 and then attached to wood cross sections that kept the airfoil’s shape. Attaching parts together was done with Plastic Fusion Epoxy Adhesive made by the Super Glue Corporation. A piece of wood 1.3 mm in thickness was used to space the gap between the airfoils during setting. The airfoil was then capped with two wooden boards and attached with epoxy to seal its sides. Holes were then drilled in both sides of the airfoil to allow for the air to enter through nozzles. The finished product can be seen in the experimental setup in Figure 7. Fig. 7.— An angled view of the airfoil in setup during experimental tests in which it was used upside down. The manometer’s capillary tube can be seen above the airfoil. A Craftsman 919.165030 air compressor was used as the air source. It was capable of delivering 0.0118 cubic meters per second at steady state when we tested it with a flow meter. The Dyson Air Multiplier patent states it delivers 0.0297 cubic meters per second. Since our airfoil has an opening which is less than half of the opening surface of the Dyson fan, this volumetric flow rate was sufficient. The air source was supplied through both sides of the airfoil along the horizontal axis using nozzles Fig. 8.— Schematic diagram of the null displacment manometer. A telescope is used to magnify the waterline in the tube. A micrometer is used to finely adjust the height of the funnel and thus the corresponding height of the water in the tube. connected to the air compressor with surgical tubing. To test steady state airflow we used the null displacement manometer. The manometer has a near instant re- another team using foam cores. A layer of 0.0089” thick action rate, which allowed us to determine if we achieved 6 oz fiberglass was laid on the foam mold covered with a steady state flow. The capillary tube being used with wax paper and cling wrap. The use of wax paper and the manometer has an outside diameter of 1.3 mm and cling wrap allowed for the foam exoskeleton to be easily an inside diameter of 0.97 mm. This is not small enough separated from the fiberglass. A thin slow hardening to measure the boundary layer at the slit, but it could epoxy was used to reduce the amount of residue left on do so farther downstream. the surface of our fiberglass airfoil(8). Another layer of Greater resolutions for measuring air flow velocities epoxy was used to smooth out the surface of the parts, have been realized for low-pressure measurements by us- and then sanded to further smooth the bumps on the ing a micrometer to read the vertical well displacement surface of the airfoil. necessary to return the meniscus to its null position as The bottom section, seen in Figure 4 is the Coanda marked by a hair line(10). This type of manometer is surface. The top section connects with the bottom sec- known as a null displacement manometer. This manome- tion on the left side of Figure 4. The two parts were built ter is connected to the stainless steel capillary tube, that with the same foam exoskeleton, and both parts were cut acts as a small probe with outer diameter 1.3 mm. Water using a jewelers saw whose small teeth make it ideal for was recommended and was used in this manometer. Our this situation. The pieces were cut to meet the require- Dyson Airfoil 5 null displacement manometer was set up with a micrometer at the base of the funnel that could be adjusted to raise or lower the water level in the tube. A telescope was anchored to the same stand as the tube end of the manometer as shown in Figure 8. The end of the objective lens of the telescope was placed 15 cm from the marking on the null displacement manometer. The funnel containing water was embedded in the hemisphere of a baseball, and its height controlled by a micrometer. A baseball was drilled so that it had a hole through its center and was then cut in half. It was used to minimize inadvertent tilting that might arise from raising and lowering the funnel. The height of this Fig. 9.— The capillary tube slightly raised above the upside down airfoil. Penicil marks along the wood and the airfoil mark every 1.27 cm (0.5”), the mark farthest to the right indicates the lowest point on the airfoil. The slit can be seen on the right side of the image. funnel controlled the level in the associated tube and the the flow we recorded video by using a high-speed cam- height of this funnel from a zero gave us an air velocity. era and fine dust. The airfoil was set up right side up The micrometer had a resolution of 200 turns per inch, and dust was dropped down from behind the airfoil. The thus giving us a velocity resolution of 0.64 m/s from the camera was run for 2 seconds capturing at 500 fps. The manometer setup. Since this was being used to probe the camera was used so that it would show the entrainment boundary layers, where we expected to see 18 m/s, this and inducement of the surrounding air into the flow cre- resolution would suffice though it was less than ideal. ated by the airfoil. The manometer was first used at an angle of zero degrees with respect to the horizontal axis. Measurements 4. RESULTS were taken vertically, along the z-axis, every 1mm. This Data was taken at an angle of 0◦ and 45◦ to the x- was done repeatedly at points every 1.27 cm (0.5”) in the axis. The first data set yielded Figure 10, while the sec- x direction along the airfoil. The first point of measure- ond data set yielded Figure 11. These figures show the ment was taken at the lowest point of the curve along velocity profiles, along with their error bars, that were the airfoil. To simplify taking these measurements the derived from many different manometer readings. The airfoil was turned upside down. This set up can been error comes from the resolution of the telescope in work- seen in Figure 9. To find all of the velocity vectors the ing with the manometer and oscillations of the water manometer was turned to an angle of 45◦ and the veloci- around the zero on the manometer. ties at that angle were then measured. Having these two Looking at the horizontal magnitudes of the flow vec- measurements of velocities at different angles allowed us tors in Figure 11 we can see how the maximum velocities to find the actual velocity vector. For the math on how follow the airfoil surface. In the progression of the veloc- to derive the velocity vector from the two measured val- ity profiles the maximum velocity follows the surface of ues, see Appendix A. With the data we were able to the airfoil or Coanda surface because of the Coanda ef- construct a directional vector field to help analyze the fect. This effect causes the fluid, in this case air, to bend boundary layer around the airfoil. upwards and follow the surface. The presence of this ef- To further our understanding of the characteristics of fect helps to verify Dyson’s patent. As the flow progesses downstream the velocity profile expands downwards and 6 reaches a more even flow. Potentially there could be a laminar flow below or past the last data points. The boundary layer is outlined here by the decrease in velocity against the airfoil from the point of the maximum velocity. In the first two velocity profiles the boundary layer was unobserved, because it was too small to be observed with the size of our capillary tube. The velocity profile that is 2.54 cm (1”) from the apex, at approximately 8 cm on the x-axis in Figure 10, the first appearance of the boundary layer is evident. The no-slip Fig. 10.— Velocity profiles along with error bars taken along the x-axis of the airfoil every 1.27 cm (0.5”). The manometer was used at an angle flat to the x-axis. condition, where the velocity is zero at the surface, is not apparent here because of the diameter of the capillary tube. Although, the boundary layer can be seen tending towards zero at the airfoil surface. In Figure 12 we present the velocity vectors along the lower surface of the airfoil. From the data collected (parallel to the horizontal axis and 45◦ below horizontal) we were able to calculate the angle of the actual velocity vector using the equations in Appendix A. These angles were then used to calculate the absolute velocity in the Fig. 11.— Velocity profiles along with error bars taken along the x-axis of the airfoil every 1.27 cm (0.5”). The manometer was used at an angle of 45◦ to the x-axis. horizontal and vertical directions. The sum of these vectors is presented in Figure 12. The dashed vertical lines represent the locations along which velocity data was collected with the manometer probe. The solid lines emanating from these vertical lines are the velocity vectors calculated at those locations. No errors are presented for this data since this would obscure details and dominate features. We observe a radical departure in our velocity vectors from the streamlines presented in Figure 3. The stream- Fig. 12.— Velocity vectors for each profile on the airfoil that can be seen in Figure 10 and Figure 11. lines in Figure 3 converge towards the lower surface of the airfoil but the velocity vectors, which represent stream- measure the boundary layer. Lastly, our airfoil surface lines, in Figure 12 diverge from the same surface. There was not completely smooth, introducing local variations are a number of reasons for this: In ourfabrication of the from what was expected. This last point however should airfoil we did not follow the designs laid out by Dyson not introduce large errors and departures from theory Corp. for their fan but rather, due to time constraints, but might explain some of the smaller irregularities. made one of similar dimensions. Due to the compar- Images of the high-speed camera can be seen in Figure atively large size of our Pitot tube we were unable to 13, these images were produced by dropping fine dust from a funnel behind the airfoil so that we could examine Dyson Airfoil Speed Inducement.png 7 high resolution and as a result had a good deal of error as compared to our therotical resolution. In the area behind the airfoil the manometer was unable to register any readings, since the velocities were below the resolution of the manometer. Sometimes it would fail to keep a consistent zero in between trials. Possible error in the manometer was contributed to moisture in the thin tubing. A better instrument for measuring velocity would have improved our data. The images acquired from the high-speed camera are unquantifiable since there were no measurements taken. The figures associated with the high-speed camera only illustrate the flow around the airfoil for the purpose of better understanding how the air moves through this area. Further studies could find a way to develop nu- Fig. 13.— The figure shows a series of frames taken from the high-speed camera to illustrate inducement. The images have an unnatural contrast that is best for viewing the dust. merical data from this kind of observation or even other the flow patterns. In Figure 13 dust is drawn in from ducement and entrainment of the airfoil design. In this behind the airfoil, or induced. Large particles and clumps way the 15-times volumetric-flow-multiplication reported of dust fall down past but small particles get pulled into by Dyson Ltd could be proven. more complex types of recording data to quantify the in- the flow indicating that there is air drawn in from behind If we had more time we would have time to experiment the airfoil. Only the finer particle clouds were induced with multiple airfoil geometeries. Initial experimentation by the airfoil. included adjusting the angle and the slit spacing of the Recording the entrainment did not work out well, as airfoil to maximize the volumetric flow. Further devel- the dust was too fine to show up on the high-speed cam- opment would have been to put multiple airfoils together era. Despite the fact that the dust dispersed greatly after to replicate the Dyson Fan design. entering the region of flow, some of the dust was still propelled nearly two meters downstream from the airfoil. While we did see that our airfoil created a region of nearly even flow on the outer edge of our airfoil, the velocity was still not high enough to be used as a practical 5. CONCLUSION wind tunnel at this scale. Furthermore we do not know The airfoil design we constructed showed interesting if this area is laminar or not. If further work could prove airflow characteristics similar to those reported by Dyson that the flow in this region is laminar this design could Ltd’s. We were able to observe the inducement of the sur- be adapted and scaled to be used as a wind tunnel. rounding air using fine dust and the high-speed camera. The Coanda effect and the boundary layer were both observed near the surface of the airfoil. 6. EQUIPMENT EXPENSES A summary of purchased equipment is shown in Ta- A large problem we faced with recording data came ble 1. John Miller provided a 1.3 mm outer diameter, from our main instrument of measurement, the null dis- .097 mm outside diamter stainless steel tube to be used placement manometer. The manometer did not have a with the null displacement manometer. All other mate- 8 TABLE 1 Equipment Purchased Product Vendor Model No. Quantity Cost ($) 6 oz S-type Fiberglass US Composities C0627S 2 yards x 27” width 14.50 1.2 Gal 635 Epoxy + 16 oz Hardner US Composities 635412 1 Kit 34.50 1/16” to 1/8” Adapter McMaster-Carr 5047K12 1 1.10 rial was scavenged from available resources and previous Brian MacMillan, and John Miller. Furthermore we experiments. The cost of equipment was supported by would like to thank group 4 consisting of Jesse Cramer, the Mechanical Engineering Department at the Univer- Alex Rosenthal, and Trey Socash for their efforts in sity of Rochester. reviewing our paper and all our past peers and colleauges who have reviewed and constructively criticized 7. ACKNOWLEDGEMENTS our work. Thereby guiding the direction of explorations. The authors would like to thank Roger Gans for his guidance. We would also like to thank Scott Russell, REFERENCES [1]Goldstein, E.,”Wind Tunnels, Don’t Count Them Out,” Aerospace America, Vol. 48 4, April 2010, pp. 38-43 [2]Dyson Bladeless Air Multiplies Laser Doppler Anemometry Results, ”http://www.dyson.com/insideDyson/”, Date Accessed 19/02/2011. [3]Gammack, P. D., Nicolas, F., Simmonds, K. J.. (2008). UK Patent Application. Application No. 0814866.0 [4]Tritton, D.J., Physical Fluid Dynamics, Van Nostrand Reinhold, 1977 (reprinted 1980), Section 22.7, The Coanda Effect. [5]Coanda, Henri, (1936). Device for Deflecting a Stream of Elastic Fluid Projected into an Elastic Fluid. US Patent No. 2052869. [6]Dyson Bladeless Air Multiplies, ”http://www.dyson.com/fans/”, Date Accessed 19/02/2011. 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