Giovanni Paolo Romano

Bio: Giovanni Paolo Romano is an academic researcher from Sapienza University of Rome. The author has contributed to research in topics: Particle image velocimetry & Turbulence. The author has an hindex of 29, co-authored 139 publications receiving 2453 citations. Previous affiliations of Giovanni Paolo Romano include Aeronáutica & Nanyang Technological University.

Experimental investigation on interactions among fluid and rod-like particles in a turbulent pipe jet by means of particle image velocimetry

Abstract: The near field of a turbulent circular pipe jet laden with rigid rod-like particles is investigated experimentally by means of particle image velocimetry. Two mass fraction loadings are examined at a Reynolds number equal to 9,000. A simple and robust phase discrimination scheme based on image intensity threshold is presented and validated. Simultaneous flow and dispersed phase velocities data are discussed and compared to literature data for spherical and elongated particles providing insight on phase interactions. Being the Stokes number around unity, both inertial and dynamical effects have high relevance, the former giving rise to velocity lag among particles and fluid and the latter to turbulence modulation in the carrier flow induced by the dispersed phase.

Spatial resolution of PIV for the measurement of turbulence

Abstract: Recent technological advancements have made the use of particle image velocimetry (PIV) more widespread for studying turbulent flows over a wide range of scales. Although PIV does not threaten to make obsolete more mature techniques, such as hot-wire anemometry (HWA), it is justifiably becoming an increasingly important tool for turbulence research. This paper assesses the ability of PIV to resolve all relevant scales in a classical turbulent flow, namely grid turbulence, via a comparison with theoretical predictions as well as HWA measurements. Particular attention is given to the statistical convergence of mean turbulent quantities and the spatial resolution of PIV. An analytical method is developed to quantify and correct for the effect of the finite spatial resolution of PIV measurements. While the present uncorrected PIV results largely underestimate the mean turbulent kinetic energy and energy dissipation rate, the corrected measurements agree to a close approximation with the HWA data. The transport equation for the second-order structure function in grid turbulence is used to establish the range of scales affected by the limited resolution. The results show that PIV, due to the geometry of its sensing domain, must meet slightly more stringent requirements in terms of resolution, compared with HWA, in order to provide reliable measurements in turbulence.

Results, outcome predictors, and complications after stapled transanal rectal resection for obstructed defecation.

Abstract: Obstructed defecation may be treated by stapled transanal rectal resection, but different complications and recurrence rates have been reported. The present study was designed to evaluate stapled transanal rectal resection results, outcome predictive factors, and nature of complications. Clinical and functional data of 123 patients were retrospectively analyzed. All patients had symptoms of obstructed defecation before surgery and had rectocele and/or intussusception. Of them, 85 were operated on by the authors and 38 were referred after stapled transanal rectal resection had been performed elsewhere. At a median follow-up of 17 (range, 3–44) months, 65 percent of the patients operated on by the authors had subjective improvement. Recurrent rectocele was present in 29 percent and recurrent intussusception was present in 28 percent of patients. At univariate analysis, results were worse in those with preoperative digitation (P < 0.01), puborectalis dyssynergia (P < 0.05), enterocele (P < 0.05), larger size rectocele (P < 0.05), lower bowel frequency (P < 0.05), and sense of incomplete evacuation (P < 0.05). Bleeding was the most common perioperative complication occurring in 12 percent of cases. Reoperations were needed in 16 patients (19 percent): 9 for recurrent disease. In the 38 patients referred after stapled transanal rectal resection, the most common problems were perineal pain (53 percent), constipation with recurrent rectocele and/or intussusception (50 percent), and incontinence (28 percent). Of these patients, 14 (37 percent) underwent reoperations: 7 for recurrence. Three patients presented with a rectovaginal fistula. One other patient died for necrotizing pelvic fasciitis. Stapled transanal rectal resection achieved acceptable results at the cost of a high reoperation rate. Patients with puborectalis dyssynergia and lower bowel frequency may do worse because surgery does not address the causes of their constipation. Patients with large rectoceles, enteroceles, digitation, and a sense of incomplete evacuation may have more advanced pelvic floor disease for which stapled transanal rectal resection, which simply removes redundant tissue, may not be adequate. This, together with the complications observed in patients referred after stapled transanal rectal resection, suggests that this procedure should be performed by colorectal surgeons and in carefully selected patients.

Particle-fluid interactions in a plane near-wall turbulent flow

Abstract: The role of particles heavier than the fluid (glass spheres in water) in a turbulent open channel flow over a smooth bed is examined at volume concentration about ), as is the Reynolds stress. These findings can be explained if they are referred to the mechanism of particle entrainment and deposition, which takes place close to the wall. This mechanism is related to particle inertia and to the dynamic of the structure of near-wall turbulence, which connects the buffer and outer regions with the very near-wall region. A significant momentum exchange between the two phases, which is particularly effective in the buffer region, is revealed by the quadrant analysis of the Reynolds stresses.

Experimental Investigation of the Propeller Wake at Different Loading Conditions by Particle Image Velocimetry

Abstract: An experimental investigation of the propeller wake in a cavitation tunnel has been performed using particle image velocimetry (PIV). A PIV image analysis algorithm implementing iterative window offset and stretching has been adopted. The main characteristics of the propeller wake at different loading conditions have been pointed out by using phase sampling techniques. Longitudinal evolution of the blade viscous wake, developing from the blade surface boundary layers, of the trailing vortex sheets, due to the radial gradient of the bound circulation, is discussed up to 1 diameter downstream. In the near field the effects of turbulent diffusion and viscous dissipation, which cause a rapid space broadening of the velocity gradients in the trailing edge wake, are also examined. In the far wake the development of the slipstream instability and the breakdown of the hub and tip vortices are outlined.

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Clinical practice guidelines in oncology

Abstract: Ductal carcinoma in situ (DCIS) of the breast represents a heterogeneous group of neoplastic lesions in the breast ducts. The goal for management of DCIS is to prevent the development of invasive breast cancer. This manuscript focuses on the NCCN Guidelines Panel recommendations for the workup, primary treatment, risk reduction strategies, and surveillance specific to DCIS.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Abstract: To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Energy dissipation rate and energy spectrum in high resolution direct numerical simulations of turbulence in a periodic box

Abstract: High-resolution direct numerical simulations (DNSs) of incompressible homogeneous turbulence in a periodic box with up to 40963 grid points were performed on the Earth Simulator computing system. DNS databases, including the present results, suggest that the normalized mean energy dissipation rate per unit mass tends to a constant, independent of the fluid kinematic viscosity ν as ν→0. The DNS results also suggest that the energy spectrum in the inertial subrange almost follows the Kolmogorov k−5/3 scaling law, where k is the wavenumber, but the exponent is steeper than −5/3 by about 0.1.