Numerical Study on Plane and Radial Wall Jets to Validate the 2D Assumption for an Idealized Downburst Outflow

Turbulent radial and plane wall jets have been extensively investigated both experimentally and numerically over the past few decades. Previous studies mostly focused on the heat and mass transfers involved in jet flows. In this study, a comprehensive investigation was conducted on turbulent radial and plane wall jets, considering both jet spread and velocity decay for different parameters. The numerical results were compared with existing experimental measurements. The comparison focused on the velocity profile, jet spread, and velocity decay, and revealed that the Reynolds stress model (RSM) performs well in the simulation of both radial and plane wall jets. The results show that with a typical ratio of cloud base height to diameter for most downburst events, the effects of nozzle height and Reynolds number on the evolution of the radial wall jet are not significant. Both the jet spread and velocity decay exhibit a clear dependence on the Reynolds number below a critical value. Above this critical value, the plane wall jet becomes asymptotically independent of the Reynolds number. The co-flow was found to have a significant influence on the evolution of the plane wall jet. Comparatively, the jet spread and velocity of the radial wall jet were faster than those of the plane jet. For applications in civil engineering, it is valid to approximate the downburst outflow with a two-dimensional (2D) assumption from the perspective of longitudinal evolution of the flows.

Study of Radial Wall Jets from Ceiling Diffusers at Variable Air Volume

The knowledge of the air velocity distribution in the supply jets is essential when designing ventilation and air conditioning systems. In this study, we tested and analyzed the velocity distributions in the radial wall jets—these jets are commonly used in ventilated rooms. Tests included jets from two ceiling diffusers of different constructions, at three airflow rates. The mean air speed distributions were measured with a 16-channel hot-sphere anemometer both in the self-similarity zone and in the terminal zone. A specially developed method of converting the mean speed to mean velocity was used. The measurement results show that the spread coefficients of the jets from both diffusers were the same, but the positions of the virtual origin were different. Due to the friction of the jet with the ceiling and the transfer of momentum to the recirculating flows, the momentum flux in the self-similarity zone decreased by up to 50%. An improved method for calculating velocity distributions in radial wall jets was developed and validated. This method takes into account the decrease of momentum, non-zero position of the jet origin, and faster velocity decrease in the terminal zone. A reliable method of predicting air velocity distribution in radial wall jets (RWJs) from ceiling diffusers may allow to properly select the diffuser size, its location, and the range of flow rate changes. The design process for variable air volume systems can be facilitated.

Radial Wall Jet Flow Over Sigmoidal Surfaces

Radial wall jet flows across flat smooth surfaces have been studied for decades. These studies show that the radial velocity of these jets decays inversely with distance from the nozzle with modest contribution from friction (Poreh, et al., 1967; Rajaratnam, 1976). However, the extent to which flat surface results apply to curved surfaces remains unclear. In this paper we explore the influence of settled particle bed slope on radial wall jet velocity profiles. Jet flows over particle beds often introduce curvature in the particle bed profile, but the influence of the developed curvature on the velocity profile has not been explored. We model the step change in thickness as a sigmoidal curve of variable steepness and use conservation of momentum to evaluate the velocity profile for steady fixed beds. We find that surface curvature has a significant influence on the velocity decay coefficients, provided there is a slip velocity in the vicinity of the particle bed interface, which is strictly true for particle surfaces. We show that the velocity profile attenuates because of curvature. Indeed, conservation of momentum predicts conditions where the forward momentum of the flow is directed completely upward. The solution identifies two new dimensionless groups that determine whether a curved surface is sufficient to block radial flow and force flow vertically.

A NEW SPECIES OF JUNIPEROXYLON FROM THE EARLY MIOCENE OF NORTHWESTERN TURKEY

Many different Cupressaceae species were described from the early Miocene of Turkey. Particularly, Glyptostroboxylon Conventz, 1885 and Taxodioxylon Hartig, 1848 from Cupressaceae are the most common genera. With the present study, a new fossil Juniperoxylon (Houlbert, 1910) Kräusel, 1949 species from early Miocene of north-western Turkey was described as Juniperoxylon acarcaea Akkemik sp. nov. The new species has diffuse and zonate axial parenchyma, 2-3 (5) cupressoid pits per cross-field, sometimes presence of crassulae, uniseriate to biseriate, opposite, frequent, contiguous and sometimes spaced radial wall pits, even uniseriate and irregularly or alternately biseriate pits on tangential walls, horizontal walls of rays smooth and/or pitted, ray width uniseriate and rarely partly biseriate, and end walls of axial parenchyma nodular and smooth. The new species is the first Juniperoxylon species description from Turkey. According to the vegetation units (VU), this fossil species may indicate the forest was likely well-drained lowland and/or upland conifer forest (VU7).

A new species of Combretum sect. Ciliatipetala (Combretaceae) from South Africa

Combretum eugeneanum, a new species from northeastern KwaZulu-Natal, South Africa and confined to the Maputaland Centre of Plant Endemism, is described, illustrated, mapped, and compared with southern African members of the genus with which it may be confused. In a narrowly defined genus Combretum, the new species belongs to Combretum sect. Ciliatipetala. In herbaria, it has usually been confused with close relatives C. apiculatum and C. edwardsii, as well as several other more distantly related members of the genus, in particular C. woodii. The new species is also closely related to the recently described C. stylesii. It is readily distinguished as an essentially glabrous woody climber or scrambling shrub needing other vegetation for support, leaf apices rarely apiculate, tertiary veins raised on the adaxial leaf surface, inflorescences few-flowered and subcapitate, upper hypanthium cupuliform, flowers with orange-red centres (discs) and peltate scales comprised of essentially eight radial cells, most of which are subdivided by at least one tangential wall, the resulting outer and inner cell(s) often with at least one additional radial wall. Combretum eugeneanum grows in Sand Forest and associated sandy bushveld, and its range and habitat does not overlap with that of C. edwardsii or C. stylesii, both of which are also very often lianas.

6066Equal significance of longitudinal and radial wall motion represents the normal right ventricular mechanical pattern: 3D echocardiographic study in 231 healthy volunteers

Three main mechanisms contribute to right ventricular (RV) pump function: (1) shortening of the longitudinal axis with traction of the tricuspid annulus towards the apex; (2) inward (radial) movement of the RV free wall, which is often referred as the “bellows effect”; and (3) bulging of the interventricular septum into the RV during the left ventricular contraction and stretching of the free wall over the septum (causing shortening in the anteroposterior direction). Despite the established clinical value of the functional changes among the aforementioned components, their relative importance remains to be quantified during physiological conditions. Accordingly, the aim of our study was to evaluate the relative contribution of the different RV motion directions to global RV function on both global and segmental level in a large set of healthy individuals. We have recruited 231 healthy volunteers (44% female, with a wide and balanced age range from 8 to 81 years) from two experienced centers performing transthoracic 3D echocardiography (3DE) on a routine basis. 3DE datasets focused on the RV were obtained using multi-beat acquisition. We determined RV volumes and subsequent ejection fraction (RVEF) by dedicated software. Using the ReVISION method, we have decomposed the motion of the RV to determine longitudinal (LEF), radial (REF) and anteroposterior ejection fraction (AEF). Their ratio to RVEF quantifies the relative contribution of the given component to global RV function. Moreover, regional subvolumes were also analyzed in a 15-segment model. Mean value of RVEF was significantly higher in female subjects compared to male subjects (60±7 vs. 56±7%, p<0.001). The relative contributions of LEF and REF to RVEF were comparable, while the contribution of AEF was significantly lower (LEF/RVEF vs. REF/RVEF vs. AEF/RVEF: 0.48±0.08 vs. 0.49±0.07 vs. 0.39±0.11, p<0.001) in the pooled population as well as in the genders separately. In line with higher RVEF found in women, female gender was associated with a higher longitudinal and radial contribution compared to males, however, AEF was similar (women vs. men; LEF/RVEF: 0.49±0.08 vs. 0.47±0.07, p<0.05; REF/RVEF: 0.50±0.07 vs. 0.48±0.06, p<0.01; AEF/RVEF: 0.38±0.12 vs. 0.40±0.10, p=NS). Interestingly, AEF/RVEF showed a significant deterioration with age (r=−0.354, p<0.001), while age-dependency of the longitudinal and radial contributions were not observed concerning both genders. An age-related decrease could be demonstrated by the volume fractions of the 5 septal volumetric segments (r=−0.229, p<0.001). Motion decomposition and the 15 segments In physiological conditions, the relative importance of longitudinal and radial wall motions is similar in determining global RV function. Aging accompanied by a decrease in anteroposterior shortening, which may point to a deteriorating systolic LV-RV interaction. Our results may facilitate further research concerning the alterations of RV mechanical pattern in various disease states.