Spherical Turbine with Skewed Axis of Rotation Design Team John Jantz, John Leo, Tahni Pierzga, Rachael Tompa, Stephen Uram Design Advisor Prof. Mohammad Taslim Sponsor Prof. Alexander Gorlov Abstract Alexander Gorlov s patent for a Universal Spherical Turbine with Skewed Axis of Rotation proposes an innovative spherical turbine with a skewed central axis. This design produces a helical blade trajectory while using blades that are easier to manufacture. By positioning the rotational axis horizontally, it is possible that the turbine will generate enough lift via Magnus and aerodynamic effects to support itself, therby expanding the placement options of the device. However, due to the highly theoretical nature of this claim, a prototype was constructed out of carbon fiber to further investigate this phenomenon. A custom testing apparatus was instrumented to correlate measured forces to the lift experienced by the turbine during wind tunnel testing. Preliminary wind-tunnel experiments indicate significant lift forces generated by the turbine, yet further data analysis will either confirm or deny the possibility of a self-supporting turbine. For more information, please contact m.taslim@neu.edu. 69
A self-supporting turbine could be placed in the jet stream where it could harness the unparalleled wind power. The lift produced by this turbine will be quantified to The Need for Project One of the claims in Gorlov s patent is that due to the spherical geometry of this turbine, it should be able to produce enough Magnus lift to be self-sustaining as long as there is an adequate wind force. This feature would allow the turbine to be placed in the jet stream where the turbine could potentially generate 10-15 MW of power due to the high wind speeds. The first step towards reaching this end goal is to quantify the lift force produced by the turbine in wind flow to determine whether or not this specific application should be pursued. The objective is to develop a working prototype of a Spherical Turbine with a Skewed Axis of Rotation that aligns with Alexander Gorlov s patent, and to fabricate a testing apparatus in order to quantify the resulting lift forces. The Design Project Objectives and Requirements Design Objectives The objectives of this project were to prototype a working turbine based off of Alexander Gorlov s patent for a Spherical Turbine with a Skewed Axis of Rotation and to test the prototype in a windtunnel to quantify the lifting force produced. Design Requirements According to the patent, the turbine should have multiple airfoil shaped blades, two of which are connected to a rotatable shaft. All of the blades should connect along an axis that is skewed between zero and 180 degrees from the rotational axis, ideally in the range of 25-35 degrees. The image from the patent is shown in the margin. To maximize the effect of the produced lift, the turbine should weigh as little as possible. The turbine and the testing apparatus must also be small enough to fit inside of the 7 x10 elliptical wind tunnel. Several design concepts were reviewed for the turbine, its components, and for the testing apparatus. Final designs were chosen due to design restraints, feasibility, and cost. Design Concepts Considered Turbine Design Candidates Although the overall design is detailed in the patent, the specifics of the blade profile, chord length, number of blades, solidity, and turbine diameter were selected through research, calculations, and necessity. The main focus points of design were the blade-to-blade connections at the hubs, shaft-to-blade connections for the axis of rotation, and manufacturing methods. The first hub design required through holes in each blade, which connected the blades to a flat circular disk via thickened standoffs, which provided material to embed a threaded insert, 70
but this was bulky. The recommended design consists of a ¼ flat plate with six arms, each with two through holes that correspond to the through holes in the blades (top image in margin). The main concern for the shaft-to-blade connection was the ability to adjust the skew angle in order to determine its effect on the lift produced. The first design required modifying the blades by drilling holes at predetermined skew angles. This concept was eliminated due to the fear of structurally weakening the blades with multiple adjacent holes. The recommended design requires three separate shafts segmented at the connections with the blades. This design allows the skew angle to easily be adjusted. Initially the clamping component was 3D printed, but it was redesigned to include structural metal plates due to the formation of cracks in the completely printed design during testing (middle image in margin). The geometry of the blades limited the possible manufacturing methods. If each blade were 3D printed it would have to be printed in sections, weakening the blades at the connection points. Machining each blade individually with a 5-axis mill or a 3-axis mill with multiple setups was considered, but proved costly. The selected option was to machine a mold (bottom image in margin), which could then be used to manufacture multiple blades. Testing Apparatus Design Candidates The first testing apparatus design consisted of a vertical post on either side of the spherical turbine shaft with slots that acted as sliders, allowing the turbine to rotate unencumbered and travel vertically due to lift. After further investigation, it was deemed that with the high wind speeds in the tunnel, this device would be difficult to anchor to prevent unwanted movement. Additionally, the frictional forces from the vertical movement of the turbine within the slider slots would induce a level of uncertainty that could skew the testing results. The recommended design utilizes the MIT wind tunnel support structure to eliminate apparatus movement due to high wind speeds. In addition, the recommended design is able to track lift forces using strain gauges, so frictional forces are no longer of concern. 71
The turbine consists of 6 blades joined at a hub to form a spherical turbine. The testing apparatus supports the turbine and measures lift. Recommended Design Concept (1) Design Description The final turbine design has a 20 diameter with 6 blades. Each blade has a cord length of 2 to achieve the desired 30% solidity. An NACA0012 airfoil cross-section was used with a 5º angle of attack to optimize performance and aerodynamic lift. The ends of the blades were flattened and thickened to provide a surface where the hub can attach via nuts and bolts. The blades also taper to a 60º angle at the ends to align under the hubs (top image in margin). The blades were manufactured using a three-part mold and a wet carbon fiber layup process (middle image in margin). The shaft is connected to the turbine via an adjustable external clamping system that slides along the blade to test different skew angles. The clamp design features two contoured 3D printed halves shaped to fit over the profile of the blade and mate with a modified sleeve bearing. A metal sleeve bearing with a setscrew is used to secure the shaft perpendicular to the blade. Metal plates add strength while clamping the bearing in place. The whole assembly is secured around the blade with nuts and bolts. The testing apparatus was designed to fit MIT s support structure, and is instrumented with a full-bridge strain gauge system positioned on two cantilever beams that support the turbine shaft (bottom image in margin). Using this method, lift can be measured by both the strain gauge system and the preexisting 6 component balance that is part of MIT s support structure. This concept eliminates any frictional considerations because the only vertical movement is due to the bending of the cantilever beams. Further, the testing apparatus contains mounted bearings that align the turbine perpendicular to the wind and contain setscrews so the turbine can be positioned easily. (2) Experimental Investigations While testing is not yet completed, data has been gathered during successful trials executed on March 21st, 2014. The turbine was tested at skew angles of 15, 20, and 30 degrees in wind speeds ranging from 20-55 mph. Initial findings conclude that the turbine s rotational speed was positively correlated to the wind speed at which it was tested (top plot in margin). Further, the testing reveals a positive trend between the lift force experienced by the turbine and its rotational speed (included at the end of this section). These findings suggest that further 72
experimentation at higher speeds will improve the plausibility of a selflifting spherical turbine. Additional testing will continue to investigate these trends, as well as explore a larger spectrum of skew angles to maximize the lift forces on the turbine. (3) Key Advantages of Recommended Concept The designs of the turbine and testing apparatus are extremely modular allowing for multiple testing setups in addition to providing ease of assembly, disassembly, and reassembly on numerous occurrences for effortless transportation and testing. The raw materials and instrumentation are the most expensive part of building a prototype turbine for testing. This turbine and testing setup totaled to $1,095. Financial Issues The financial scope of this project included manufacturing the prototype and testing apparatus. The largest cost should have been the mold used to produce the blades, but it was machined free of charge, as were the hubs. Totaling $445, the main costs for the turbine were the carbon fiber and the resin. The testing apparatus totaled $650, which included the instrumentation and raw materials. The welding and additional resources for design modification were provided free of charge. A portion of the cost for the turbine and the testing apparatus went towards hardware as well as some bulk materials such as mold wax, release, and application tools. The total cost of this project was less than that of a similar project done at the University of Washington that cost a total of $2500. The turbine would benefit from blades accurately machined out of a light and uniform material, and professional blade balancing. Recommended Improvements The turbine could be improved by having the blades machined from a uniform, lightweight material. This would alleviate any false results due to turbine imbalance. To further optimize the turbine, additional experimentation should be conducted where the angle of attack of the blades is tested, as well as the solidity. 73