From The Whiting School of Engineering
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4.15.24
Lisa Ercolano
The inspiration from Leonardo da Vinci
The Federal Aviation Administration fields thousands of complaints each year about the characteristic loud buzzing produced as drone propellers slice through the air. In fact, a 2017 NASA study showed that people find drone noise more annoying than that of any other ground vehicle, even when they’re at the same volume. And experts believe such noise pollution will only worsen as unmanned aerial vehicles are increasingly used for package delivery, photography, emergency response, and more.
But there’s new hope for quieter skies overhead. A research team led by Rajat Mittal, a Johns Hopkins professor of mechanical engineering, believes a device invented by Leonardo da Vinci more than 500 years ago may hold the key to softer sounding drones.
“Da Vinci’s visionary aerial screw—a sort of precursor to the modern helicopter—inspired our investigation,” Mittal says. “The idea was to bring historical inspiration and modern computation together to reimagine a quieter modern drone.”
Mittal collaborated with a team that included Jung-Hee Seo, a Johns Hopkins associate research professor of mechanical engineering, and Suryansh Prakhar, a JHU doctoral candidate in Mechanical Engineering. Their work appeared in the Bulletin of the American Physical Society and was presented at the Annual Meeting of the Division of Fluid Dynamics in Washington in November 2023.
The team was aware that other research groups had explored loop-shaped propellers that were less noisy than traditional propellers with their flat, thin blades and angled edges. The characteristic buzzing sound produced by traditional propellers is the result of “tip vortices”—small swirling tornadoes of air that whoosh and intersect with the flat, angled blades. Loop propellers spread those vortices around, muting the sound.
Mittal’s team surmised that Leonardo’s design, with its screwlike shape and single blade, might be even quieter.
Boundary of Swirling Air Currents (vortices) Around a Propeller
To find out, the researchers needed to create a model, which required selecting the most accurate measurements and design features. They came across a project in which aerospace engineering students at the University of Maryland had analyzed the aerial screw’s design, including its radius, curve, pitch, shape, and number of loops. In doing so, they brought to life the device depicted in Leonardo’s sketch, proving his design could actually take flight.
“Using that project as a starting point, we constructed a 3D model of the da Vinci aerial screw’s looped shape, and then used our simulation software, called ViCar3D, to simulate the flow of air around the rotor as the drone was hovering in place. The software then predicted the speed of airflow around the propeller and pressure patterns,” Prakhar says.
The pressure generated on the rotating screw’s surface would turn into sound, so the team used a Farassat formulation—a theory devised by a NASA scientist in the late 1970s in order to predict sound levels based on simulated airflow patterns—to calculate the noise produced 5 meters from the rotor. Then they simulated a canonical loop propeller in the same circumstances.
The da Vinci propeller was, in fact, a bit noisier than the loop propeller at any given rotation speed. But the aerial screw also produced more lift—the upward force that opposes gravity’s downward pull. The researchers also knew that the amount of lift needed to remain fixed for common drone assignments such as delivering packages, so they then calculated the noise emitted by the da Vinci and loop propellers when producing the same amount of lift.
At last, they had their answer.
“The da Vinci propeller produced much less noise for the same given amount of lift being generated,” Prakhar says.
The team next plans to conduct more simulations to model the propellers’ noise levels when the drones are larger and operating at higher speeds.
“We would expect similar results in noise reduction,” Prakhar says. “However, the aerodynamic efficiency of da Vinci’s propeller will be lower when compared to a traditional propeller, since not all parts of the spiral screw shape can be optimized to produce a similar amount of lift force. Despite this possible loss in efficiency, these propeller shapes can be useful for applications where noise reduction is more important than aerodynamic efficiency.”
See the full article here.
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The G.W.C. Whiting School of Engineering is a division of The Johns Hopkins University located in the university’s Homewood campus in Baltimore, Maryland.
Engineering at Johns Hopkins was originally created in 1913 as an educational program that included exposure to liberal arts and scientific inquiry. In 1919, the engineering department became a separate school, known as the School of Engineering. By 1937, over 1,000 students had graduated with engineering degrees. By 1946 the school had six departments.
In 1961, the School of Engineering changed its name to the School of Engineering Sciences and, in 1966, merged with the Faculty of Philosophy to become part of the School of Arts and Sciences. In 1979, the engineering programs were organized into a separate academic division that was named the G.W.C. Whiting School of Engineering. The school’s named benefactor is George William Carlyle Whiting, co-founder of The Whiting-Turner Contracting Company.
Several departments at the school have been nationally and historically recognized. The Johns Hopkins Department of Biomedical Engineering is recognized as the top-ranked program in the nation. The Department of Geography and Environmental Engineering has consistently ranked as one of the top 5 programs nationally by U.S. News & World Report in recent years.
The Department of Mechanical Engineering is well known for its fundamental and historic contributions, especially in the fields of mechanics and fluid dynamics. Although it has always been a very small department, an uncharacteristically large number of highly acclaimed scholars have been associated with it over the years. These include Clifford Truesdell, Owen Martin Philips, Jerald Ericksen, James Bell, Stanley Corrsin, Robert Kraichnan, John L. Lumley, Leslie Kovasznay, Walter Noll, K. R. Sreenivasan, Hugh Dryden, Shiyi Chen, Andrea Prosperetti, Fazle Hussain, Harry Swinney, Stephen H. Davis, Gregory L. Eyink, Charles Meneveau, Joseph Katz (professor), Lauren Marie Gardner, Gretar Tryggvason and Mohamed Gad-el-Hak. Many of the landmark papers in the field of fluid mechanics (turbulence in particular) were written using data from the Corrsin Wind Tunnel Laboratory. The wind tunnel is still in operation today. The department was also home to the school of rational mechanics. It was recently ranked as one of the top 5 departments in the nation for research activity by the National Research Council (the department was ranked 13th by the generic U.S. News & World Report rankings), and is still considered one of the main centers of fundamental research in fluid dynamics and solid mechanics.
Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”
The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”
What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.
The Johns Hopkins University is a private research university in Baltimore, Maryland. Founded in 1876, the university was named for its first benefactor, the American entrepreneur and philanthropist Johns Hopkins. His $7 million bequest (approximately $147.5 million in today’s currency)—of which half financed the establishment of the Johns Hopkins Hospital—was the largest philanthropic gift in the history of the United States up to that time. Daniel Coit Gilman, who was inaugurated as the institution’s first president on February 22, 1876, led the university to revolutionize higher education in the U.S. by integrating teaching and research. Adopting the concept of a graduate school from Germany’s historic Ruprecht Karl University of Heidelberg, [Ruprecht-Karls-Universität Heidelberg] (DE), Johns Hopkins University is considered the first research university in the United States. Over the course of several decades, the university has led all U.S. universities in annual research and development expenditures. The university has graduate campuses in Italy, China, and Washington, D.C., in addition to its main campus in Baltimore.
Johns Hopkins is organized into 10 divisions on campuses in Maryland and Washington, D.C., with international centers in Italy and China. The two undergraduate divisions, the Zanvyl Krieger School of Arts and Sciences and the Whiting School of Engineering, are located on the Homewood campus in Baltimore’s Charles Village neighborhood. The medical school, nursing school, and Bloomberg School of Public Health, and Johns Hopkins Children’s Center are located on the Medical Institutions campus in East Baltimore. The university also consists of the Peabody Institute, Applied Physics Laboratory, Paul H. Nitze School of Advanced International Studies, School of Education, Carey Business School, and various other facilities.
Johns Hopkins was a founding member of the American Association of Universities. Nobel laureates and Fields Medalists have been affiliated with Johns Hopkins. Founded in 1883, the Blue Jays men’s lacrosse team has captured national titles.
Research
The opportunity to participate in important research is one of the distinguishing characteristics of Hopkins’ undergraduate education. About 80 percent of undergraduates perform independent research, often alongside top researchers. Johns Hopkins has members of the Institute of Medicine, The Howard Hughes Medical Institute Investigators, The National Academy of Engineering, and The National Academy of Sciences. Nobel Prize winners have been affiliated with the university as alumni, faculty members or researchers.
The Johns Hopkins University is among the most cited institutions in the world ranking No. 3 globally [after Harvard University and The MPG Society (DE)] in the number of total citations published in Thomson Reuters-indexed journals over 22 fields in America.
Johns Hopkins received research grants from The National Aeronautics and Space Administration, as a leading recipient of NASA research and development funding. Totals include grants and expenditures of JHU’s Applied Physics Laboratory in Laurel, Maryland.
The Johns Hopkins University also offers the “Center for Talented Youth” program—a nonprofit organization dedicated to identifying and developing the talents of the most promising K-12 grade students worldwide. As part of the Johns Hopkins University, the “Center for Talented Youth” or CTY helps fulfill the university’s mission of preparing students to make significant future contributions to the world. The Johns Hopkins Digital Media Center (DMC) is a multimedia lab space as well as an equipment, technology and knowledge resource for students interested in exploring creative uses of emerging media and use of technology.
In 2013, the Bloomberg Distinguished Professorships program was established by a $250 million gift from Michael Bloomberg. This program enables the university to recruit fifty researchers from around the world to joint appointments throughout the nine divisions and research centers. For The American Academy of Arts and Sciences each professor must be a leader in interdisciplinary research and be active in undergraduate education. Directed by Vice Provost for Research, there are Bloomberg Distinguished Professors at the university, including Nobel Laureates, fellows of the American Association for the Advancement of Science, members of the American Academy of Arts and Sciences, and members of the National Academies.
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