Romain Fiévet

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Verified

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• PhD
• Research Scientist at Max Planck Institute for Meteorology

Plain Language Summary Convective cold pools (CPs) are regions of cool air forming beneath precipitating clouds. As rain droplets evaporate during their fall, they cool down the surrounding air, thereby increasing its weight and causing it to sink down. As the cold sinking airflow hits the ground, it spreads outward in all directions, creating stro...

Clustering of tropical thunderstorms constitutes an important climate feedback because it influences the radiative balance. Convective self‐aggregation (CSA) is a profound modeling paradigm for explaining the clustering of tropical oceanic thunderstorms. However, CSA is hampered in the realistic limit of fine model resolution when cold pools—dense...

Characteristic boundary conditions for the Navier-Stokes equations (NSCBC) are implemented for the first time with discontinuous spectral methods, namely the spectral difference and flux reconstruction. The implementation makes use of the resolution by these methods of the strong form of the Navier-Stokes equations by applying these conditions thro...

The effect of thermal nonequilibrium on flame ignition and stabilization in supersonic scramjet combustors is studied using reaction-layer resolved high resolution numerical simulations. The flow configuration is based on the HyShot-II experiment, with a sonic H2 jet injected into a supersonic crossflow. A detailed H2/air chemical kinetics model is...

Plain Language Summary In simulations that mimic the atmosphere over tropical ocean surfaces with constant temperature, thunderstorms can spontaneously group together, forming large cloud patches surrounded by clear areas. This clustering tends to happen when the ocean surface is warm enough; otherwise, the thunderstorms remain scattered. Recent si...

The diurnal variability in sea surface temperature (SST) may play an important role in cloud organization above the tropical ocean, with implications for precipitation extremes, storminess, and climate sensitivity. Recent cloud-resolving simulations demonstrate how imposed diurnal SST oscillations can strongly and delicately impact mesoscale convec...

The diurnal variability of sea surface temperature (SST) may play an important role for cloud organization above the tropical ocean, with implications for precipitation extremes, storminess, and climate sensitivity. Recent cloud-resolving simulations demonstrate how imposed diurnal SST oscillations can strongly, and delicately, impact mesoscale con...

Recent observations and modeling increasingly reveal the key role of cold pools in organizing the convective cloud field. Several methods for detecting cold pools in simulations exist, but are usually based on buoyancy fields and fall short of reliably identifying the active gust front. The current cold pool (CP) detection and tracking algorithm (C...

Convective cold pools (CPs) mediate interactions between convective rain cells and help organize thunderstorm clusters, in particular mesoscale convective systems and extreme rainfall events. Unfortunately, the observational detection of CPs on a large scale has been hampered by the lack of relevant near‐surface data. Unlike numerical studies, wher...

Tropical convective rainfall is known to vary with the diurnal cycle, yet it is also influenced by large scale convergence. In a suite of idealized cloud-resolving numerical experiments, we mimic Earth's Hadley cell to probe the interactions between oscillations in rainfall inherent to the large-scale circulation and the rainfall oscillation caused...

Recent observations and modeling increasingly reveal the key role of cold pools in organizing the convective cloud field. Several methods for detecting cold pools in simulations exist, but are usually based on buoyancy fields and fall short in reliably identifying the active gust front. The current algorithm, termed CoolDeTA, aims to detect and tra...

The diurnal variability of sea surface temperature (SST) may play an important role for cloud organization above the tropical ocean, with implications for precipitation extremes, storminess, and climate sensitivity. Recent cloud-resolving simulations demonstrate how imposed diurnal SST oscillations can strongly, and delicately, impact mesoscale con...

The attenuation power of an acoustic liner is optimized by unsteady compressible flow simulations that model the presence of the liner with a time-domain impedance boundary condition (TDIBC). Two test cases are considered: a one-dimensional impedance tube and a two-dimensional grazing incidence tube. The impact of the liner on the pressure field is...

A high-order spectral difference flow solver is used to perform direct numerical simulations (DNS) of a hypersonic laminar boundary layer on an ultrasonically absorptive coating (UAC), in order to analyze the stabilizing effects of such a material on the laminar–turbulent transition. The UAC is modeled in the simulations by a time-domain impedance...

Clustering of tropical thunderstorms constitutes an important climate feedback because it influences the heat radiated to space. Convective self-aggregation (CSA) is a profound modelling paradigm for explaining the clustering of tropical oceanic thunderstorms. However, CSA is hampered in the realistic limit of fine model resolution when cold pools...

The rotating detonation engine is increasingly favored as a viable pressure gain combustion technology for both propulsion and power generation applications. Practical designs involve the discrete injection of fuel and air, which then partially mix to produce the reactive mixture that is processed by a continuously moving detonation wave within the...

In flows where the relaxation rate of molecular vibrational energy to equilibrium is comparable to the flow through timescales, the presence of turbulence can alter the mixing and equilibration processes. To understand the coupling between mixing and vibrational relaxation, a novel state-specific species model is solved in a background turbulent fl...

In dual-mode scramjet engines, the isolator comprises complex shock structures that provide the necessary compression of incoming air to sustain combustion farther downstream. This region of pressure increase is termed a pseudoshock. For stable scramjet design, it is essential to ensure sufficient length of isolator to fit the pseudoshock and achie...

Analysis of dual-model scramjet engines often rely on the assumption of thermally perfect gas, where the internal modes of molecular motion are assumed to be in thermal equilibrium. With an increase in enthalpy and in the presence of shocks and expansion waves, the equilibrium assumption does not hold within a scramjet inlet-isolator section. For t...

The practical realization of supersonic flight relies on the development of a robust propulsion system. These air-breathing scramjet engines process fuel and high-speed air to generate propulsive thrust. Unlike conventional jet engines, scramjets achieve efficient thrust by compressing air through a system of shocks. As a result, the reliability of...

A dataset of normal shock trains in a rectangular cross-section channel has been created from direct numerical simulations in an effort to quantify the impact of inflow confinement ratio on the shock-train structure. To this end, the inlet boundary-layer momentum thickness was varied while the bulk inflow and outflow conditions remained constant. T...

A dataset of normal shock trains in a rectangular cross-section channel has been created from Direct Numerical Simulations (DNS) in an effort to quantify the impact of inflow confinement ratio on the shock train structure. To this end, only the inlet boundary layer momentum thickness was varied while the bulk inflow and outflow conditions remained...

The spatial evolution of acoustic waveforms produced by a laboratory-scale Mach 3 jet are investigated using both 1∕4 and 1∕8 in. pressure field microphones located along rays emanating from the postpotential core where the peak sound emission is found to occur. The measurements are acquired in a fully anechoic chamber, where ground or other large...

The spatial evolution of acoustic waveforms produced by a Mach 3 jet are investigated using both 1/4 inch and 1/8 inch pressure field microphones located along rays emanating from the post potential core where the peak sound emission is found to occur. The measurements are acquired in a fully anechoic chamber where ground, or other large surface re...

A Large Eddy Simulation of a fully expanded heated supersonic jet flow is examined using acoustic source indicators based on simplification to the Lighthill tensor. This is done in an effort to explore the utility of such methods in defining a rationalized indicator that would help guide future experiments using high-speed PIV, and the accuracy of...