Numerical and experimental investigations of the flow-pressure relation in multiple sequential stenoses coronary artery

Cardiovascular Aspects of Radiolog

TRY plant trait database – enhanced coverage and open access

Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives

An assessment of the ship drag penalty arising from light calcareous tubeworm fouling

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 was found that this surface had a ks = 0.325 mm, substantially less than previously reported values for light calcareous fouling. Any number of variations in surface topology could account for these different report values, such as sparseness, differences in species settlement etc. The experimental results were used to predict the drag on a fouled full scale ship. To achieve this, a modified method for predicting the total drag of a spatially developing turbulent boundary layer(TBL), such as that on the hull of a ship, is presented. The method numerically integrates the skin friction over the length of the boundary layer, assuming a widely accepted analytical form for the mean velocity profile of the TBL. The velocity profile contains the roughness (fouling) information, such that the prediction requires only an input of ks, free-stream velocity (ship speed), kinematic viscosity and the length of the boundary layer (hull length). Using the equivalent sandgrain roughness height determined from experiments, a FFG-7 Oliver Perry class Frigate is predicted to experience a 23% increase in total resistance at cruise, if its hull is coated in light calcareous tubeworm fouling. A similarly fouled Very Large Crude Carrier would experience a 34% increase in total resistance at cruise

Linear and non-linear forced response of a conical, ducted, laminar premixed flame

This paper presents an experimental study on the dynamics of a ducted, conical, laminar premixed flame subjected to acoustic excitation of varying amplitudes. The flame transfer function is measured over a range of forcing frequencies and equivalence ratios. In keeping with previous works, the measured flame transfer function is in good agreement with that predicted by linear kinematic theory at low amplitudes of acoustic velocity excitation. However, a systematic departure from linear behaviour is observed as the amplitude of the velocity forcing upstream of the flame increases. This non-linearity is mostly in the phase of the transfer function and manifests itself as a roughly constant phase at high forcing amplitude. Nonetheless, as predicted by non-linear kinematic arguments, the response always remains close to linear at low forcing frequencies, regardless of the forcing amplitude. The origin of this phase behaviour is then sought through optical data post-processing

Amplitude and frequency modulation in wall turbulence

In this study we examine the impact of the strength of the large-scale motions on the amplitude and frequency of the small scales in high-Reynolds-number turbulent boundary layers. Time series of hot-wire data are decomposed into large- and small-scale components, and the impact of the large scale on the amplitude and frequency of the small scales is considered. The amplitude modulation effect is examined by conditionally averaging the small-scale intensity () for various values of the large-scale fluctuation (). It is shown that increases with increasing value of in the near-wall region, whereas, farther away from the wall, decreases with increasing . The rate of increase in small-scale intensity with the strength of the large-scale signal is neither symmetric (about ) nor linear. The extent of the frequency modulation is examined by counting the number of occurrences of local maxima or minima in the small-scale signal. It is shown that the frequency modulation effect is confined to the near-wall region and its extent diminishes rapidly beyond . A phase lag between the large- and small-scale fluctuations, in terms of amplitude modulation, has also been identified, which is in agreement with previous studies. The phase lag between large- and small-scale fluctuations for frequency modulation is comparable to that of amplitude modulation in the near-wall region. The combined effect of both amplitude and frequency modulation is also examined by computing conditional spectra of the small-scale signal conditioned on the large scales. In the near-wall region, the results indicate that the peak value of pre-multiplied spectra increases with increasing value of , indicating amplitude modulation, while the frequency at which this peak occurs also increases with increasing value of , revealing frequency modulation. The overall trends observed from the conditional spectra are consistent with the results obtained through statistical analyses. Finally, a physical mechanism that can capture most of the above observations is also presented

Three-dimensional conditional structure of a high-Reynolds-number turbulent boundary layer

An array of surface hot-film shear-stress sensors together with a traversing hot-wire probe is used to identify the conditional structure associated with a large-scale skin-friction event in a high-Reynolds-number turbulent boundary layer. It is found that the large-scale skin-friction events convect at a velocity that is much faster than the local mean in the near-wall region (the convection velocity for large-scale skin-friction fluctuations is found to be close to the local mean at the midpoint of the logarithmic region). Instantaneous shear-stress data indicate the presence of large-scale structures at the wall that are comparable in scale and arrangement to the superstructure events that have been previously observed to populate the logarithmic regions of turbulent boundary layers. Conditional averages of streamwise velocity computed based on a low skin-friction footprint at the wall offer a wider three-dimensional view of the average superstructure event. These events consist of highly elongated forward-leaning low-speed structures, flanked on either side by high-speed events of similar general form. An analysis of small-scale energy associated with these large-scale events reveals that the small-scale velocity fluctuations are attenuated near the wall and upstream of a low skin-friction event, while downstream and above the low skin-friction event, the fluctuations are significantly amplified. In general, it is observed that the attenuation and amplification of the small-scale energy seems to approximately align with large-scale regions of streamwise acceleration and deceleration, respectively. Further conditional averaging based on streamwise skin-friction gradients confirms this observation. A conditioning scheme to detect the presence of meandering large-scale structures is also proposed. The large-scale meandering events are shown to be a possible source of the strong streamwise velocity gradients, and as such play a significant role in modulating the small-scale motions

Non k-type behaviour of roughness when1 in-plane wavelength approaches the2 boundary layer thickness3

A surface roughness from a recently cleaned and painted ship hull was scanned, scaled and replicated for laboratory testing to systematically investigatethe influence of the ratio of in-plane roughness wavelength,λ, with respect to the boundary layer thickness δ. The experiments were performed by geometrically scaling the surface which maintains a constant effective slopeESxand solidityΛ, while the ratio ofλ~δis varied. Here we scale the scanned roughness topography by a factor of 2.5 and, and measure the18mean velocity profiles in the turbulent boundary layers developing over these surfaces at a range of freestream velocities and streamwise measurement locations. The results show that the 2.5×scaled roughness, which hasλ~δ≪1 behaves in the expectedk-21type manner, with a roughness function∆U+that is proportional to the viscous scaled roughness height. The 15×surface, however, which hasλ~δ≈1, exhibits very different nonk-type behaviour. This larger surface does not approach the fully rough asymptote and also exhibits a drag penalty that is comparable to the 2.5×case despite the six-fold increase in the roughness height. Measurements on a spanwise/wall-normal plane reveal that the 15×surface has introduced a large scale spanwise variation in mean streamwise velocity (dispersive stresses) that extend far beyond the logarithmic region. Together this evidence suggests that a demarcation betweenk-type and nonk-type behaviour can occur in situations where the in-plane roughness wavelength approachesthe boundary layer thickness. This finding has important implications to how we scale smallscale roughness from high Relarge-scale applications for testing in lowResmall-scale laboratory facilities or simulations

Dataset for a paper titled "Non k-type behaviour of roughness when 1 in-plane wavelength approaches the 2 boundary layer thickness"

This dataset has the velocity profile data as well as the roughness function data from wind tunnel measurements obtained at 2 different streetwise locations with two different scaled rough surfaces. The attached zip file has 2 subfolders that contain the data at 2m downstream and 4m downstream. The measurements were carried out at 10, 15, 20 and 25 m/s for both surfaces. The zip file also contains a .mat file, which has the original scan of the surface. Note that the scan is the inverse of the surface geometry. Therefore, the values need to be multiplied by -1 to get the actual surface geometry. If you are using this dataset, please cite this paper: B. Nugroho, J. P. Monty, I.K.A.P Utama, B. Ganapathisubramani and N. Hutchins, &quot;Non k-type behaviour of roughness when in-plane wavelength approaches the boundary layer thickness&quot;, Journal of Fluid Mechanics, https://doi.org/10.1017/jfm.2020.875</span

A direct comparison of pulsatile and non-pulsatile rough-wall turbulent pipe flow

Pulsatile rough-wall turbulent pipe flow is compared against its non-pulsatile counterpart using data obtained from direct numerical simulation. Results are presented at a mean friction Reynolds number of 540 for a set of three geometrically scaled roughness topographies at a single forcing condition, which, based on existing classifications, falls into the current-dominated very-high-frequency regime. By comparing the pulsatile data against an equivalent non-pulsatile dataset (Chan et al., J. Fluid Mech., vol. 854, 2018, pp. 5–33), the key differences (and similarities) between the forced and unforced configurations are identified. A major finding of this study is that the flow in the outer region retains its self-similar functional form under pulsatile rough-wall conditions, and, as a result, Townsend’s outer-layer similarity hypothesis holds for the roughness-forcing combinations considered here. On the other hand, the unsteady cases exhibit a rich array of flow physics in the region beneath the roughness crests not observed in the steady case. These differences are examined using a Moody chart, which encapsulates how the hydraulic properties of pulsatile rough-wall pipe flow differ from their non-pulsatile counterpart.T. O. Jelly, R. C. Chin, S. J. Illingworth, J. P. Monty, I. Marusic and A. Oo