Deep Dive into NTP Pool's Popularity and Mapping

Time synchronization is of paramount importance on the Internet, with the Network Time Protocol (NTP) serving as the primary synchronization protocol. The NTP Pool, a volunteer-driven initiative launched two decades ago, facilitates connections between clients and NTP servers. Our analysis of root DNS queries reveals that the NTP Pool has...

Design of a Direct numerical Simulation of flow and heat transfer in a T-junction

Several investigations have been undertaken to study the velocity and temperature fields associated with the thermal mixing between fluids, and resulting thermal striping in a T-junction. However, the available experimental databases are not sufficient to describe the involved physics in adequate detail, and, due to experimental limitations,...

Intercept and Inject: DNS Response Manipulation in the Wild

DNS is a protocol responsible for translating human-readable domain names into IP addresses. Despite being essential for many Internet services to work properly, it is inherently vulnerable to manipulation. In November 2021, users from Mexico received bogus DNS responses when resolving whatsapp.net. It appeared that a BGP route leak diverged DNS...

Assessing e-Government DNS Resilience

Electronic government (e-gov) enables citizens and residents to digitally interact with their government via the Internet. Underpinning these services is the Internet Domain Name Systems (DNS), which maps e-gov domain names to Internet addresses. Structuring DNS with multiple levels of redundancy that can withstand stress events such as denial...

Transitional Flow Dynamics Behind a Micro-Ramp

Micro-ramps are popular passive flow control devices which can delay flow separation by re-energising the lower portion of the boundary layer. We compute the laminar base flow, the instantaneous transitional flow, and the mean flow around a micro-ramp immersed in a quasi-incompressible boundary layer at supercritical roughness Reynolds number...

Analyzing a turbulent pipe flow via the one-point structure tensors: Vorticity crawlers and streak shadows

Efforts to identify and visualize near-wall structures typically focus on the region y⁺≳5, where large-scale structures with significant turbulent kinetic energy content reside, such as the high-speed and low-speed streaks associated with sweep and ejection events. While it is true that the level of the turbulent kinetic energy...

A measurement study of DNSSEC misconfigurations

DNSSEC offers protection against spoofing of DNS data by providing origin authentication, ensuring data integrity and authentication of non-existence by using public-key cryptography. Although the relevance of securing a technology as crucial to the Internet as DNS is obvious, the DNSSEC implementation increases the complexity of the deployed...

Transport of suspended particles in turbulent open channel flows

Two experiments are performed in order to investigate suspended sediment transport in a turbulent open channel flow. The first experiment used particle image velocimetry (PIV) to measure the fluid velocity with a high spatial resolution, while particle tracking velocimetry (PTV) was used to measure the velocity of individual sediment particles....

Numerical Simulation of Turbulent Flow in Concentric Annuli

In this paper we consider a fully developed turbulent flow in a round pipe with a small inner annulus. The diameter of the inner annulus is less than 10% of the diameter of the outer pipe. As a consequence, the surface area of the inner pipe compared to the outer pipe is small. The friction exerted by the wall on the flow is proportional to the...

Aeroacoustics of compressible subsonic jets: Direct Numerical Simulation of a low Reynolds number subsonic jet and the associated sound field

Jet noise is an extensively studied phenomenon since the deployment of the first civil jet aircraft more than 50 years ago. Jet noise makes up a considerable portion of the total noise of jet aircraft, and the expansion of the numbers of airplanes and airports has only been possible by keeping the noise of airplanes under control. However, while...

Particle Sedimentation in Wall-Bounded Turbulent Flows

In this work, a comparison between the results of point-particle direct numerical simulations and PIV/PTV experiments of a particle-laden horizontal channel flow is presented. The numerical simulations were preformed trying to mimic as much as possible the experimental conditions. The accuracy of the point-particle approach was evaluated by...

Particle Sedimentation in Wall-Bounded Turbulent Flows

In this work, a comparison between the results of point-particle direct numerical simulations and PIV/PTV experiments of a particle-laden horizontal channel flow is presented. The numerical simulations were preformed trying to mimic as much as possible the experimental conditions. The accuracy of the point-particle approach was evaluated by...

A zonal characteristic boundary condition for numerical simulations of aerodynamic sound

This paper presents a non-reflecting boundary condition that significantly reduces the spurious pressure oscillations that are produced when vortical structures in a compressible flow cross the computational farfield boundaries. The method is based on commonly used characteristic boundary conditions. Here, incoming characteristics are ramped to...

DNS simulations of lean premixed flame kernels with flamelet generated manifolds: An overview

In this paper recent developments in the application of the method of flamelet generated manifolds (FGM) to simulations of turbulent premixed combustion are considered. Initially the method was developed for kinetic reduction for simulations of laminar combustion using stationary solvers. Recently the method was extended to direct numerical...

Direct numerical simulation of the flow around an airfoil with unsteady wake

Direct numerical simulations of a NACA-0012 airfoil at zero degrees incidence are presented for a range of Mach and Reynolds numbers. At Reynolds number 10,000, the flow around the airfoil is found to be dominated by vortex shedding from an unstable wake. Frequencies are found to collapse using a Strouhal number based on trailing edge...

Noise due to unsteady flow past trailing edges

This paper presents two-dimensional direct numerical simulations (DNS) of noise generated at trailing edges (TE) with zero thickness. The simulations are conducted specifying either no-slip or slip walls in order to investigate viscous effects. In both cases, small amplitude disturbances are introduced close to the inflow boundary that serve as...

Direct numerical simulation of the turbulent flow around an airfoil using spectral/HP method

Since the accuracy of the widely used Reynolds Averaged Navier Stokes (RANS) approach is limited simulating turbulent flow separation on airfoils, we applied a spectral/hp element method to predict the turbulent flow separation at an airfoil for an angle of attack of 12°. The spectral/hp approach allows to solve the incompressible Navier-Stokes...