In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between those layers.
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid with surfaces defined by boundary conditions. With high-speed supercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems. Ongoing research yields software that improves the accuracy and speed of complex simulation scenarios such as transonic or turbulent flows. Initial validation of such software is typically performed using experimental apparatus such as wind tunnels. In addition, previously performed analytical or empirical analysis of a particular problem can be used for comparison. A final validation is often performed using full-scale testing, such as flight tests.
In common usage, wind gradient, more specifically wind speed gradient or wind velocity gradient, or alternatively shear wind, is the vertical component of the gradient of the mean horizontal wind speed in the lower atmosphere. It is the rate of increase of wind strength with unit increase in height above ground level. In metric units, it is often measured in units of meters per second of speed, per kilometer of height (m/s/km), which reduces inverse milliseconds (ms−1), a unit also used for shear rate.
The surface layer is the layer of a turbulent fluid most affected by interaction with a solid surface or the surface separating a gas and a liquid where the characteristics of the turbulence depend on distance from the interface. Surface layers are characterized by large normal gradients of tangential velocity and large concentration gradients of any substances transported to or from the interface.
In meteorology, the planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL) or peplosphere, is the lowest part of the atmosphere and its behaviour is directly influenced by its contact with a planetary surface. On Earth it usually responds to changes in surface radiative forcing in an hour or less. In this layer physical quantities such as flow velocity, temperature, and moisture display rapid fluctuations (turbulence) and vertical mixing is strong. Above the PBL is the "free atmosphere", where the wind is approximately geostrophic, while within the PBL the wind is affected by surface drag and turns across the isobars.
In fluid dynamics, turbulence modeling is the construction and use of a mathematical model to predict the effects of turbulence. Turbulent flows are commonplace in most real-life scenarios. In spite of decades of research, there is no analytical theory to predict the evolution of these turbulent flows. The equations governing turbulent flows can only be solved directly for simple cases of flow. For most real-life turbulent flows, CFD simulations use turbulent models to predict the evolution of turbulence. These turbulence models are simplified constitutive equations that predict the statistical evolution of turbulent flows.
The Wingless Electromagnetic Air Vehicle (WEAV) is a heavier than air flight system developed at the University of Florida, funded by the Air Force Office of Scientific Research. The WEAV was invented in 2006 by Dr. Subrata Roy, plasma physicist, aerospace engineering professor at the University of Florida, and has been a subject of several patents. The WEAV employs no moving parts, and combines the aircraft structure, propulsion, energy production and storage, and control subsystems into one integrated system.
Mujeeb R. Malik is a Pakistani born American aerospace engineer serving as Senior Aerodynamicist at NASA Langley Research Center. He is known for his research in boundary layer stability, laminar-turbulent transition, computational methods and aerodynamic simulations. He was the architect of CFD Vision 2030, a NASA-sponsored study to advance the state-of-the-art of computational fluid dynamics (CFD) by exploiting high performance computing and modern validation experiments.
Paul Andrews Libby was a professor of mechanical and aerospace engineering at the University of California, San Diego, a specialist in the field of combustion and aerospace engineering.
Peyman Givi is a Persian-American rocket scientist and engineer.
A bypass transition is a laminar–turbulent transition in a fluid flow over a surface. It occurs when a laminar boundary layer transitions to a turbulent one through some secondary instability mode, bypassing some of the pre-transitional events that typically occur in a natural laminar–turbulent transition.
Joseph Katz is an Israel-born American fluid dynamicist, known for his work on experimental fluid mechanics, cavitation phenomena and multiphase flow, turbulence, turbomachinery flows and oceanography flows, flow-induced vibrations and noise, and development of optical flow diagnostics techniques, including Particle Image Velocimetry (PIV) and Holographic Particle Image Velocimetry (HPIV). As of 2005, he is the William F. Ward Sr. Distinguished Professor at the Department of Mechanical Engineering of the Whiting School of Engineering at the Johns Hopkins University.
Fotis Sotiropoulos is a Greek-born American engineering professor and university administrator known for his research contributions in computational fluid dynamics for river hydrodynamics, renewable energy, biomedical and biological applications. He currently serves as the Provost and Senior Vice President for Academic Affairs of Virginia Commonwealth University, a position he has held since August 1, 2021
Leslie S. G. Kovasznay was a Hungarian-American engineer, known as one of the world's leading experts in turbulent flow research.
James Eugene "Gene" Broadwell was an American aeronautical engineer, known for the Broadwell model. The model consists of a set of differential equations, describing the structure of a shock wave in a simple discrete velocity gas.
Reda R. Mankbadi is the founding Dean of the Engineering College at Embry-Riddle Aeronautical University. He is a former NASA senior scientist at NASA's Glenn Research Center and a Fellow of the NASA Lewis Research Academy. Mankbadi has published over 150 scientific papers.
Kenneth Breuer is an American academic, who is a Professor of Engineering and Professor of Ecology, Evolution, and Organismal Biology at Brown University and the director of the Center of Fluid Mechanics at Brown University. He is a fellow of the American Physical Society (APS), American Society of Mechanical Engineers (ASME), and Associate Fellow of the American Institute of Aeronautics and Astronautics (AIAA), and a Society of Integrative and Comparative Biology member.
Dennice Fanny Maynard Gayme is mechanical engineer whose research combines control theory and fluid dynamics in boundary layer control and its applications including ship resistance and propulsion and the design of wind farms. Educated in Canada and the US, she works in the US as a professor and Carol Croft Linde Faculty Scholar in the Johns Hopkins University Department of Mechanical Engineering.
Hassan M. Nagib is a mechanical engineer, aerospace engineer, and academic. He is the John T. Rettaliata Professor of Mechanical and Aerospace Engineering at the Illinois Institute of Technology and was also the Founding Director of the institute's Fluid Dynamics Research Center.
Joaquim R. R. A. Martins is an aerospace engineer, academic, and author. He is the Pauline M. Sherman Collegiate Professor in the Department of Aerospace Engineering at the University of Michigan, where he directs the Multidisciplinary Design Optimization Laboratory. He also has a courtesy appointment in the Department of Naval Architecture and Marine Engineering.
