On the role of secondary motions in turbulent square duct flow

We use a direct numerical simulations (DNS) database for turbulent flow in a square duct up to bulk Reynolds number \Rey_b=40000, to quantitatively analyze the role of secondary motions on the mean flow structure. For that purpose we derive a generalized form of the identity of Fukagata, Iwamoto and Kasagi (FIK), which allows to quantify the effect of cross-stream convection on the mean streamwise velocity, wall shear stress and bulk friction coefficient. Secondary motions are found to contribute for about $6\%$ of total friction, and to act as a self-regulating mechanism of turbulence whereby wall shear stress nonuniformities induced by corners are equalized, and universality of the wall-normal velocity profiles is established. We also carry out numerical experiments whereby the secondary motions are artificially suppressed, in which case their equalizing role is partially taken by the turbulent stresses

How Age Matters in the Assessment of Vertigo in the Pediatric Emergency Department: A 10-Year Age-Stratified Etiology Survey

Vertigo is a relatively frequent cause for referral to the pediatric emergency department, and it is usually caused by benign or self-limiting etiology. However, it could be difficult to evaluate especially in the younger child and could also conceal serious illness as encephalitis or cerebellitis. Our survey collected in a 10-year period 757 children assessed in pediatric emergency department for vertigo and stratified this population for etiology and for group of age: younger than 6 years (113, 14.9%), between 7 and 12 years (251, 33.2%), and older than 12 years (393, 51.9%). In addition, associated signs and symptoms, evaluation by a neurologist or an otorhinolaryngologist, and instrumental investigations were recorded.We found that age is the most important variable to assess the possibility of a central nervous system disease as etiology cause of vertigo with a significant difference of incidence between the younger group (younger than 6 years, 23%) and older groups (3% and 1%; P < 0.001).This finding should reinforce the index of suspicion for a central nervous system illness as cause of vertigo in the preschool children with an accurate workup including evaluation by a neurologist or an otorhinolaryngologist and instrumental investigations as needed

Copy number variation, gene expression and histological localization of human beta-defensin 2 in patients with adeno-tonsillar hypertrophy

Both bacterial infections and innate oral immunity response participate in development of adeno-tonsillar hypertrophy (ATH). ATH can lead to obstructive sleep apnea. We investigated the beta-defensin 2 (hBD-2) encoding gene, DEFB4, by analyzing the copy number variations (CNVs) of the defensin gene cluster in patients with ATH and by correlating CNV with DEFB4 gene expression. We enrolled 79 patients with ATH, 21 of whom presented with only adenoid hypertrophy, while 58 exhibited hypertrophy of both adenoid and tonsil. CNVs of the defensin gene cluster, DEFB4 mRNA, and hBD-2 protein expression were assessed. Also, beta-defensin 2 was localized histologically using immunohistochemistry. The distribution of defensin gene cluster CNV was similar among the 79 subjects. DEFB4 expression analysis exhibited considerable inter-individual variability, but with neither specific differences among subjects nor correlation with the CNV number. Immunohistochemistry enabled localization of hBD-2 in the tonsil and adenoid epithelium. No differences in localization between the two ATH presentations were found. Inducible antimicrobial defensin peptides exhibited great inter-individual variability in terms of both CNV and gene expression, but no correlation with presentation of ATH was found

Presentazione

Il contributo presenta i contributi della sezione monografica dedicata al centenario della Costituzione del Liechtenstei

Optimal transient growth in compressible turbulent boundary layers

The structure of zero-pressure-gradient compressible turbulent boundary layers is analysed using the tools of optimal transient growth theory. The approach relies on the extension to compressible flows of the theoretical framework originally developed by Reynolds & Hussain (J. Fluid Mech., vol. 52, 1972, pp. 263–288) for incompressible flows. The model is based on a density-weighted triple decomposition of the instantaneous field into the contributions of the mean flow, the organized (coherent) motions and the disorganized background turbulent fluctuations. The mean field and the eddy viscosity characterizing the incoherent fluctuations are here obtained from a direct numerical simulation database. Most temporally amplified modes (optimal modes) are found to be consistent with scaling laws of turbulent boundary layers for both inner and outer layers, as well as in the logarithmic region, where they exhibit a self-similar spreading. Four free-stream Mach numbers are considered: $\mathit{Ma}_{\infty }=0.2$, 2, 3 and 4. Weak effects of compressibility on the characteristics length and the orientation angles are observed for both the inner- and the outer-layer modes. Furthermore, taking into account the effects of mean density variations, a universal behaviour is suggested for the optimal modes that populate the log layer, regardless of the Mach number. The relevance of the optimal modes in describing the near-wall layer dynamics and the eddies that populate the outer region is discussed

Early evolution of the compressible mixing layer issued from two turbulent streams

Direct numerical simulation of the spatially developing mixing layer issuing from two turbulent streams past a splitter plate is carried out under mild compressibility conditions. The study mainly focuses on the early evolution of the mixing region, where transition occurs from a wake-like to a canonical mixing-layer-like behaviour, corresponding to the filling-up of the initial momentum deficit. The mixing layer is found to initially grow faster than linearly, and then at a sub-linear rate further downstream. The Reynolds stress components are in close agreement with reference experiments and follow a continued slow decay till the end of the computational domain. These observations are suggestive of the occurrence of incomplete similarity in the developing turbulent mixing layer. Coherent eddies are found to form in the close proximity of the splitter plate trailing edge, that are mainly organized in bands, initially skewed and then parallel to the spanwise direction. Dynamic mode decomposition is used to educe the dynamically relevant features, and it is found to be capable of singling out the coherent eddies responsible for mixing layer development.PRACE Research Infrastructur

Numerical analysis of sound radiation from rotating discs

The analysis of sound radiation from rotating elastic discs, e.g. saw blades, is an interesting research topic. Especially for people who work in the vicinity of such machines, health related issues with respect to noise exposure levels gain more and more awareness. Therefore, the industry is faced with the challenge of developing quieter products in order to improve the working environment and to extend the time a worker can use these tools before a harmful situation arises. Moreover, less noise emission means less energy consumption and therefore a higher productivity. In this paper, the authors investigate the sound radiation from a rotating disc where the sound power is used as a global measure for the acoustic performance. Different methods for calculating the sound power of a spinning saw blade are compared. These are a fully coupled finite element approach, a hybrid finite element/boundary element approach, a simplified form of the Rayleigh integral known as the lumped parameter model, and the equivalent radiated sound power. The results show good agreement between the costly full models and those utilizing approximation methods which can save remarkable computational costs. The proposed frame can be used in optimization procedures for developing quieter saw blades and other rotating discs. Furthermore, the paper discusses mode splitting which is a well-known phenomenon for rotating machinery. For this, the results of sound radiation are investigated with respect to the question whether mode splitting is actually audible

Otolarylogical features in a cohort of patients affected with 22q11.2 deletion syndrome: a monocentric survey

Otorhinolaryngologic manifestations are common in 22q11.2 deletion syndrome (22q11.2DS), but poorly described. This study aimed to better define the ear-nose-throat (ENT) phenotype of 22q11.2DS patients, in the attempt to best detect subjects requiring subspecialist intervention. We enrolled 25 patients affected with 22q11.2DS. Anatomic and functional ENT findings were investigated using clinical, laboratory and instrumental data. Immunophenotype and frequency of infections were evaluated. Univariate and multivariate analyses were performed. ENT anomalies were found in 88% of patients, and in 20% congenital palate defects required surgery. Adenoids hypertrophy or palatine tonsils hypertrophy were noted in 80 and 48%. Fourty-eight percent of subjects had rhinolalia/phonia, severe in half of these. We also found nasal regurgitation or laryngeal penetration/aspiration in 20 and 16%, respectively. Instrumental exams revealed a mild conductive hypoacusia in 32% (bilateral in most cases), tympanometric anomalies in 28%, and swallowing abnormalities in 16%. Statistical univariate analysis showed a direct association between rhinolalia/phonia and episodes of laryngeal aspiration (P=0.016) and between tympanometric anomalies and increased adenoid volume (P=0.044). No association between episodes of food aspiration and palatal anomalies was found. Moreover, no statistically significant association was observed between the number of airway infections and the ENT findings. This study contributes to better define the ENT phenotype in patients with 22q11.2DS, helpful to prevent potential complications. Furthermore, the identification of a subcategory of patients may allow the early adoption of specific speech therapy programs to improve the clinical outcome of 22q11.2DS patients