In this Letter, we study the interaction between a self-sustaining exothermic reaction front propagating in a direction perpendicular to that of gravity and the buoyancy-driven convective flow during ...frontal polymerization (FP) of a low-viscosity monomer resin. As the polymerization front transforms the liquid monomer into the solid polymer, the large thermal gradients associated with the propagating front sustain a natural convection of the fluid ahead of the front. The fluid convection in turn affects the reaction-diffusion (RD) dynamics and the shape of the front. Detailed multiphysics numerical analyses and particle image velocimetry experiments reveal this coupling between natural convection and frontal polymerization. The frontal Rayleigh (Ra) number affects the magnitude of the velocity field and the inclination of the front. A higher Ra number drives instability during FP, leading to the observation of thermal-chemical patterns with tunable wavelengths and magnitudes.
An experimental investigation of the turbulent boundary layer around 2D permeable and impermeable obstacles was carried out using high-resolution particle image velocimetry (PIV) in a large-scale ...refractive-index-matching (RIM) flume. The flow over three rectangular obstacles was studied including an impermeable model (case 1), a model porous through only its flow-facing surface (case 2), and an obstacle porous through both its flow-facing and upper surfaces (case 3). The ratio of the height (
h
) to the incoming boundary layer thickness (
δ
0
) was
h
/
δ
0
≈
1
/
4
. Measurements were performed at a Reynolds number
Re
= 70,000 based on the freestream velocity and
δ
0
. The results highlight the impact of permeability on the mean flow, separation bubble, Reynolds shear stress, as well as the level and production of turbulent kinetic energy. In particular, the momentum deficit and flow reattachment downstream of the obstacle were highly sensitive to the permeability. Similarly, the second-order statistics of the velocity in the vicinity of the three obstacles exhibited large variations. It is shown that constraining and channeling the flow through only the flow-facing surface of the obstacle (case 2) result in lower momentum deficit, turbulence levels, and Reynolds shear stress in the intermediate and far wake regions. Overall, the results highlight the distinctive effects of obstacle permeability on the turbulent boundary layer.
In a series of wind-tunnel experiments conducted at the St. Anthony Falls Laboratory, a wind-turbine model was exposed to three different thermal regimes (neutral, weakly stable and weakly convective ...flows) in three simple arrangements relevant to wind-farm applications: single turbine in the boundary-layer, aligned turbine-turbine, and an upwind three-dimensional sinusoidal hill aligned with the turbine. Results focus on the spatial evolution of large-scale motions developing over the different thermal and topographic boundary conditions, and on their influence on the mean and fluctuating angular velocity of the turbine rotor. As compared to the single turbine case, both the upwind hill and turbine caused a reduction in the mean angular velocity regardless of the thermal regime; the turbine angular velocity fluctuations always decreased with a turbine upwind, which depleted the energy of the large structures of the flow; however such fluctuations decreased (increased) under stably stratified (convective) conditions when the hill was present. Pre-multiplied spectra of the rotor angular velocity and two-point correlation contours of the streamwise velocity component confirmed a non-trivial link between thermal stratification and terrain complexity. It is inferred that the thermal effects occurring in the three different boundary-layer regimes modulate the spanwise motion of the hill wake and define whether the hill shelters or exposes the turbine to enhanced large-scale energetic motions.
Field and laboratory experiments were performed to unravel the structure of the power output fluctuations of horizontal-axis wind turbines based on incoming flow turbulence. The study considers the ...power data of three wind turbines of rotor sizes 0.12, 3.2, and 96 m, with rated power spanning six decades from the order of 10
0
to 10
6
W. The 0.12 m wind turbine was tested in a wind tunnel while the 3.2 and 96 m wind turbines were operated in open fields under approximately neutrally stratified thermal conditions. Incoming flow turbulence was characterised by hotwire and sonic anemometers for the wind tunnel and field set-ups. While previous works have observed a filtering behaviour in wind turbine power output, this exact behaviour has not, to date, been properly characterised. Based on the spectral structure of the incoming flow turbulence at hub height, and the mechanical and structural properties of the turbines, a physical basis for the behaviour of temporal power fluctuations and their spectral structure is found with potential applications in turbine control and numerical simulations. Consistent results are observed across the geometrical scales of the wind turbines investigated, suggesting no Reynolds number dependence in the tested range.
Bosutinib is approved for newly diagnosed Philadelphia chromosome-positive (Ph+) chronic phase (CP) chronic myeloid leukemia (CML) and for Ph+ CP, accelerated (AP), or blast (BP) phase CML after ...prior treatment with tyrosine kinase inhibitors (TKIs). In the ongoing phase 4 BYOND study (NCT02228382), 163 CML patients resistant/intolerant to prior TKIs (n = 156 Ph+ CP CML, n = 4 Ph+ AP CML, n = 3 Ph-negative/BCR-ABL1+ CML) received bosutinib 500 mg once daily (starting dose). As of ≥1 year after last enrolled patient (median treatment duration 23.7 months), 56.4% of Ph+ CP CML patients remained on bosutinib. Primary endpoint of cumulative confirmed major cytogenetic response (MCyR) rate by 1 year was 75.8% in Ph+ CP CML patients after one or two prior TKIs and 62.2% after three prior TKIs. Cumulative complete cytogenetic response (CCyR) and major molecular response (MMR) rates by 1 year were 80.6% and 70.5%, respectively, in Ph+ CP CML patients overall. No patient progressed to AP/BP on treatment. Across all patients, the most common treatment-emergent adverse events were diarrhea (87.7%), nausea (39.9%), and vomiting (32.5%). The majority of patients had confirmed MCyR by 1 year and MMR by 1 year, further supporting bosutinib use for Ph+ CP CML patients resistant/intolerant to prior TKIs.
Wind tunnel experiments were performed to study the effect of passive flow control strategies on the wake and drag of a semicircular cylinder of infinite aspect ratio. High-resolution planar particle ...image velocimetry was used to obtain flow statistics around the semicircular cylinder at Reynolds number
R
e
≈
3.2
×
10
4
based on the cylinder diameter. The control mechanisms under consideration include rigid flaps of various lengths placed at the edges of the structure and a small slot along the symmetry plane of the cylinder. Mean velocity fields reveal the distinctive effects of each passive mechanism on the flow, such as velocity recovery, size of the recirculation bubble and location of the reattachment point. The distributions of turbulence kinetic energy and kinematic shear stress show the modulation of each passive control mechanism on the wake, including the onset and location of the maximum turbulence levels. Instantaneous and mean fields of swirling strength further highlight the role of the passive mechanisms in the vortex dynamics. Drag coefficient for the various cases was estimated indirectly from the flow measurements using a momentum balance. This approach shows that long flaps and slot were able to reduce drag with respect to the base case. The rigid flaps with length coincident with the diameter of the cylinder offered the best performance with drag reduction of
∼
25
%
.
Wind tunnel experiments were performed to characterize the flow-induced rotations and pitching of various flat plates as a function of the thickness ratio and the location of the axis of rotation. ...High-resolution telemetry, laser tachometer, and hotwire were used to get time series of the plates motions and the signature of the wake flow at a specific location. Results show that small axis offset can induce high-order modes in the plate rotation due to torque unbalance, and can trigger self-initiated pitching. The spectral decomposition of the flow velocity in the plate wake reveals the existence of a dominating high-frequency mode that corresponds to a static-like vortex shedding occurring at the maximum plate pitch. The associated characteristic length scale is the projected width at maximum pitching angle. The increase of the plate thickness ratio implies lower angular velocity in rotation cases. A simple model based on aerodynamic forces is used to explain the linear relation between pitching frequency and wind speed, the pitching frequency increase with axis offset, and the onset of pitching.
We present an implementation of super-large-scale particle image velocimetry (SLPIV) to characterize spatially the turbulent atmospheric boundary layer using natural snowfall as flow tracers. The ...SLPIV technique achieves a measurement area of ~22 m × 52 m, up to 56 m above the ground, with a spatial resolution of ~0.34 m. The traceability of snow particles is estimated based on their settling velocity obtained from the wall-normal component of SLPIV velocity measurements. The results are validated using coincident measurements from sonic anemometers on a meteorological tower situated in close proximity to the SLPIV sampling area. A contrast of the mean velocity and the streamwise Reynolds stress component obtained from the two techniques shows less than 3 and 12 % difference, respectively. Additionally, the turbulent energy spectra measured by SLPIV show a similar inertial subrange and trends when compared to those measured by the sonic anemometers.
The scale-dependent response of an instrumented full-scale wind turbine is studied under neutrally stratified conditions. The analysis is focused on the linkage between the incoming flow, turbine ...power output and foundation strain. Wind speed, measured from sonic anemometers installed on a meteorological tower, and foundation strain were sampled at 20 Hz, while the turbine power was sampled at 1 Hz. A wavelet framework and structure function are used to obtain cross correlations among flow turbulence, turbine power and strain across scales as well as to quantify intermittent signatures in both flow and turbine quantities. Results indicate that correlation between the streamwise velocity component of the wind flow and turbine power is maximised across all scales larger than the rotor radius for wind measured at the turbine hub height. The characteristic time lag associated with maximum correlation is shown to be consistent with the Taylor's hypothesis for turbulent scales smaller than the separation between the meteorological tower and the turbine. However, it decreases with increasing scale size and diminishes to zero at scales on the order of the boundary layer thickness. Turbine power and strain fluctuations exhibited practically the same behaviour at scales larger than two rotor diameters. At those scales, the cross correlation between these quantities resulted ∼0.99 and remains still over 0.9 at the scale of rotor radius. Below this scale, the correlation decreases logarithmically with scale. The strong linkage between power and strain for all the relevant scales would eventually allow the analysis of dynamic forcing on the foundation based on the power output. Intermittency on the flow is shown to be transferred and amplified by the turbine, leading to highly intermittent power output.
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