arXiv subjects

Elmer M. Gennaro

Publications and source records attributed to Elmer M. Gennaro.

3 recordsLinked to original sources

arXiv2026

Numerical method for strongly variable-density flows at low Mach number: flame-sheet regularisation and a mass-flux immersed boundary method

A low-Mach-number flow, in the laminar regime, has intrinsically two characteristic spatial scales for a given time scale, or two characteristic temporal scales for a given spatial scale, and these dual scales are very different due to the disparity between the flow and acoustic speed. Therefore low-Mach-number flows impose mathematical and computational challenges in their description. Standard numerical methods for compressible flows, which are typically designed for problems with a single dominant spatial and temporal scale, require alternative approaches such as preconditioning techniques or solvers tailored for low-Mach-number equations. The present work introduces a simplified fluid dynamics model for flows at low Mach number, based on the fractional time-step method. The proposed approach is suitable for handling strong temperature gradients and thermal diffusion, as encountered in combustion systems. To address discontinuities at the flame front in reacting-flow cases, due to the hypothesis of infinitely fast chemistry, a regularisation procedure is employed. Additionally, the immersed boundary method (IBM) is extended to handle mass flux across the boundary surface, enabling simulations of fuel ejection from an arbitrary burner geometry, using a convenient Cartesian grid. The numerical method utilises a predictor-corrector scheme for time integration on a collocated grid, with flux interpolation to prevent numerical pressure oscillations (``odd-even decoupling''). Relevant test cases are used to verify the methods and their implementations, demonstrating correctness and robustness.

physics.flu-dyn↗

arXiv2026

Counterflow around a cylinder

The incompressible flow around a circular cylinder, positioned at the center of an unconfined planar counterflow, is studied by means of numerical solutions of the conservation equations and linear stability analysis. The flow is completely defined by the Reynolds number ($\Rey$) -- based on the cylinder radius, the strain rate defining the counterflow, and the kinematic viscosity. For very low values of $\Rey$, the flow is steady, two-dimensional, and fully attached to the cylinder wall. Increasing $\Rey$ above $\Rey_s \approx 16.86$, the flow separates, giving rise to two symmetric, counter-rotating recirculation regions on each side of the cylinder. Further increasing $\Rey$ leads to a progressive enlargement of the recirculation regions and the appearance of multiple recirculation centers, akin to Moffatt eddies. However, the convective acceleration imposed by the counterflow limits their size. An oscillatory mode becomes linearly unstable for $\Rey_{c} \approx 4146$. This mode gives rise to a sinuous meandering of the wake flow, on each side of the cylinder, being analogous to the well-known von Kármán instability. The frequency of this mode is directly proportional to the strain rate defining the counterflow.

physics.flu-dyn↗

arXiv2025

Effectiveness of Quota Policies Across STEM, Biological, and Humanities Programs

We examine more than a decade of quota policy at Unesp, analyzing Physics, Biology, and Pedagogy as representative programs of distinct assessment styles. Quotas show little impact in Physics, where the admission barrier is low, and in Pedagogy, where high pass rates make it difficult to differentiate students, but they reveal systematic differences in Biology. Focusing the analysis on Calculus I - an introductory course in Physics and other Science, Technology, Engineering, and Mathematics (STEM) programs - for which much larger statistics are available, a clear hierarchy emerges: students admitted through open competition perform best, those from public schools achieve intermediate results, and students from racial quotas perform worst. When students are divided directly by the admittance exam grade, the performance difference is even clearer. Statistical analysis also shows that, contrary to expectation, the probability of passing decreases as the number of attempts increases, indicating that initial educational gaps are difficult to overcome within higher education.

physics.soc-ph↗