A test coupon coated with light calcareous tubeworm fouling was scanned, scaled and reproduced for wind-tunnel testing to determine the equivalent sand grain roughness ks. It found that this surface had a ks = 0.325 mm, substantially less than previously reported values fouling. This result used predict drag on fouled full scale ship. To achieve this, modified method predicting total of spatially developing turbulent boundary layer (TBL), such as hull ship, is presented. The numerically...

Microplastics are particles less than 5 mm in size and a growing scientific concern, given the potential harm caused across ecosystems as result of global use plastics. Most microplastics non-spherical shape, however, most atmospheric modelling studies to date treat simple spheres when assessing transport. To further understand effects shape on microplastic transport, HYSPLIT model was utilized identify differences. It shown that extent transport deposition varied significantly by for larger...

The scale interactions occurring within a turbulent boundary layer are investigated in the presence of free-stream turbulence. turbulence is generated by an active grid. free stream monitored single-component hot-wire probe, while second probe roved across height at same streamwise location. Large-scale structures shown to penetrate and increase velocity fluctuations throughout. It speculated that, depending on extent penetration, i.e. based level turbulence, near-wall production peaks...

It is a known phenomenon that some dielectric materials used to construct plasma actuators degrade during operation. However, the rate at which this process occurs, what extent, as well method monitor yet be established. In experimental study, it shown electrical measurements can changes in material of actuators. The procedure we introduce for monitoring follows from work Kriegseis, Grundmann, and Tropea [Kriegseis et al., J. Appl. Phys. 110, 013305 (2011)], who Lissajous figures measure...

In this study, the development of a boundary layer past change in surface roughness (from rough to smooth, $\text{R}\rightarrow \text{S}$ ) is examined. Measurements flow were made by hot wires, whereas friction velocity was estimated Preston tube measurements. By means diagnostic plot turbulence intensity, it shown that above internal exhibits characteristics rough, wall-bounded flow, near wall intensity similar an isolated smooth wall. Similarly, viscous scaling mean streamwise shows...

Closed-loop feedback control of boundary layer streaks embedded in a laminar and experiencing transient growth, which is inherent to bypass transition, experimentally investigated. Streaky disturbances are introduced by spanwise array cylindrical roughness elements, counter disturbance provided plasma actuators, capable generating spanwise-periodic rotating vortices the layer. Feedback shear stress sensors. An input/output model system obtained from measurements response steady forcing, used...

This study investigates vortex shedding characteristics from a circular cylinder subjected to yaw oscillations. The considers two length-to-diameter ratios (13 and 20) Reynolds numbers (5×103 1.5×104). Yaw oscillations ranging θ=0° 30° are considered at various reduced frequencies 0.25 4. Vortex behavior the mid-span of is measured using hot-wire anemometry. Planar particle image velocimetry (PIV) measurements used visualize near wake. It shown that an increase in frequency leads shift range...

An extensive parametric study of the response a Blasius boundary layer to forcing by spanwise arrays plasma actuators was performed. The actuator are designed produce streamwise-oriented vortex pairs, which cause streaks alternating low and high streamwise velocity. This work is motivated closed-loop control bypass transition. measured using hot-wire anemometry over distance approximately 100 boundary-layer thicknesses. resulting periodic disturbance velocity decomposed into Fourier modes....

This research compares the e↵ect of plasma actuators on 3D incompressible boundary layer flow in experiments and direct numerical simulations. The are arranged to produce stream-wise streaks e↵ectively cancel out dominant structures bypass transition, thereby delaying transition turbulence. simulations resolve all relevant scales fluid approximate force from with a body model. Good agreement exists between time-averaged velocity fields at downstream plane. Our long term goal is delay...

The overarching objective motivating this work is a physical demonstration of modelbased, closed-loop control bypass transition using plasma actuators. present concerned with the This manuscripts extends by Hanson et al., 1,2 who demonstrated that spanwise array actuators can produce significant attenuation transient growth disturbances introduced roughness elements. In work, loop closed based on feedback from wall-shear stress measurements. signal empirical modelling input/output flow...

This study is motivated by controlling transient growth and subsequent bypass transition of the laminar boundary layer to turbulence. In experiments employing a model problem, an active roughness element used introduce steady/unsteady streak disturbances in Blasius layer. tractable arrangement enables systematic investigation evolution potential methods control them real time. The strategy utilizes wall-shear-stress sensors, upstream downstream plasma actuator, as inputs model-based...

The response of a zero-pressure-gradient laminar boundary layer to forcing by spanwise array plasma actuators is investigated experimentally. used in this study are designed produce counter-rotating vortex pairs periodic arrangement inside the layer. It was demonstrated Hanson et al., related studies, that actuator can be successfully control transient growth instability occurring Blasius However, it also effectiveness could greatly affected geometry, which affects modal content and energy...

This work is concerned with the design of a leading edge for flat-plate model used to study laminar and transitional boundary layers. For this study, flow over complete boundary-layer model, including edge, flat section, trailing-edge flap, modeled. The effect important geometrical features on resulting pressure distribution, starting from well-known symmetric modified super ellipse, investigated. A minimal gradient measurement side plate achieved using an asymmetrical configuration...

Particle image velocimetry measurements are performed to examine the spatial structure in boundary layers under influence of free-stream turbulence (FST). A similarity structural organization inside layer is found between present FST cases and canonical flows.

The objective of this study was to investigate a method monitor the health plasma actuators. Common actuator dielectric materials were used in research, namely Kapton polyimide tape, and those manufactured from printed circuit boards (PCB) having FR-4 composite material. Actuators utilizing these are known visually degrade during operation. However, quantitative measure degradation actuators has not yet been examined. A parametric identify role operational parameters, excitation voltage...

This work is concerned with the response of a Blasius boundary layer to plasma actuators for purpose using these devices in bypass transition control. The structure actuator-induced streaks measured hot-wire anemometry over streamwise distance approximately 100 thicknesses, based on thickness 4 mm at point actuation. Spanwise power spectra disturbance velocity show that 90% energy contained within mode related spanwise spacing exposed actuator electrodes, and its first 3 harmonics. modal...