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Fig. 1

Transition under elevated free-stream turbulence

Elevated free-stream turbulence accelerates the process of laminar-to-turbulent transition by the selective inclusion of low-frequency disturbances into the boundary layer. As these amplify, they form longitudinal streaks that rapidly break-down into localized regions of turbulence that resemble the turbulent spots studied here under low free-stream turbulence. The manner in which free-stream turbulence alters the spot-growth […]

Fig. 2

Laminar-to-turbulent transition in separation bubbles

The transition of fluid flows from a laminar behaviour to turbulence–referred to as laminar-to-turbulent transition–is one of the chief difficulties in classical physics. While laminar flows are orderly, turbulence involves irregular velocity fluctuations over a wide range of spatial and temporal scales. The fluctuations enhance the transfer of momentum and energy so that the drag […]

Fig. 3

Instability of planar free shear layers

The instability of planar free shear layers is an important consideration in a broad range of applications, such as heat exchangers, chemical reactors, building wakes, and aerofoils. A planar free shear layer is primarily unstable through an inviscid Kelvin-Helmholtz mode that exists due to the inflectional shape of the shear-layer velocity profile. The OKCFD Lab performs detailed numerical research […]

Growth mechanisms of a turbulent spot

Growth mechanisms of a turbulent spot

Hairpin-like vortices have been identified as the dominant coherent flow structures in transitional and turbulent boundary layers and free shear layers. To better understand the characteristics of these flows, it is important to study the creation and growth mechanisms of the hairpin vortices and the resultant wave packets containing multiples of these flow structures. A turbulent spot in […]

Instantaneous iso-surfaces of static pressure fluctuations inside a lobed mixer.

Mixing mechanisms in an axisymmetric lobed mixer

Due to steadily-increasing pressure from the public and from air-traffic regulators, aircraft and engine manufacturers are aggressively researching methods for reducing the level of noise of aircraft during landing and take-off. Generally, exhaust noise reduction is achieved by mixing the high-speed exhaust stream with the lower-speed bypass stream exiting the engine. A lobed mixer enhances […]