David Richter

• PhD
• Professor (Associate) at University of Notre Dame

Fluid thermodynamics underpins atmospheric dynamics, climate science, industrial applications, and energy systems. However, direct numerical simulations (DNS) of such systems are computationally prohibitive. To address this, we present a novel physics-informed spatio-temporal surrogate model for Rayleigh-B\'enard convection (RBC), a canonical examp...

Meteorological processes such as gust fronts, roll structures, internal boundary layer development, and smaller scale turbulence complicate the physical interpretation of measured aerosol particle properties, fluxes, and transport in the marine atmospheric boundary layer (MABL). To better decipher maritime aerosol measurements by aircraft, ships, a...

When turbulent convection interacts with a turbulent shear flow, the cores of convective cells become aligned with the mean current, and these cells (which span the height of the domain) may interact with motions closer to the solid boundary. In this work, we use coupled Eulerian-Lagrangian direct numerical simulations of a turbulent channel flow t...

The intermittency of coherent turbulent structures in the tropical cyclone boundary layer makes them challenging to fully characterize, especially regarding their impact on momentum dynamics in the eyewall. Furthermore, the fine spatial and temporal model resolution needed to resolve these structures has long impeded their understanding. Using the...

Fog constitutes a thick, opaque blanket of air hugging Earth’s surface, laden with small water droplets or ice crystals. Fog disrupts transportation, poses security threats, disorients human perception, and impacts communications and ecosystems. Collusion of atmospheric, terrestrial, and hydrologic processes produces fog droplets that pullulate ove...

When turbulent convection interacts with a turbulent shear flow, the cores of convective cells become aligned with the mean current, and these cells (which span the height of the domain) may interact with motions closer to the solid boundary. In this work, we use coupled Eulerian-Lagrangian direct numerical simulations of a turbulent channel flow t...

Cloud microphysics fulfills a fundamental role in the formation and evolution of marine fog, but it is not fully understood. Numerous studies have addressed this by means of direct observations and modeling efforts. However, collision–coalescence of aerosols and fog droplets is a process often neglected. In this study we perform an analysis of the...

Developing reduced order models for the transport of solid particles in turbulence typically requires a statistical description of the particle-turbulence interactions. In this work, we utilize a statistical framework to derive continuum equations for the moments of the slip velocity of inertial settling Lagrangian particles in a turbulent boundary...

Improved representation of turbulent processes in numerical models of tropical cyclones (TCs) is expected to improve intensity forecasts. To this end, the authors use a large-eddy simulation (with 31-m horizontal grid spacing) of an idealized category 5 TC to understand the role of turbulent processes in the inner core of TCs and their role on the...

It has long been known that under the right circumstances, inertial particles (such as sand, dust, pollen, or water droplets) settling through the atmospheric boundary layer can experience a net enhancement in their average settling velocity due to their inertia. Since this enhancement arises due to their interactions with the surrounding turbulenc...

Under the right circumstances, inertial particles (such as sand or dust) settling through the atmospheric boundary layer can experience a net enhancement in their average settling velocity due to their inertia. Since this enhancement arises due to their interactions with the surrounding turbulence it must be modelled at coarse scales. Models for th...

Western Alaska regularly experiences storm surge events induced by extra-tropical storms, most active during fall, winter, and spring. Among others, the presence of sea ice in Western Alaska seawater poses a challenge in modeling storm surge in this area. Existing storm surge models rarely consider sea ice effects together with wind-induced wave ef...

Predicting the rapid intensification (> 15.0 m s ⁻¹ increase in 10m wind speed over 24 hours or less) of tropical cyclones (TC) remains a challenge in the broader context of numerical weather prediction largely due to their multiscale dynamics. Ocean observations show that the size and magnitude of sea surface temperature (SST) anomalies associated...

The Pi Chamber generates moist turbulent Rayleigh-Bénard flow in order to replicate steady-state cloud conditions. We take inspiration from this setup and consider a particle-laden, convectively driven turbulent flow using direct numerical simulation. The aim of our paper is to develop a simple stochastic model that can accurately describe the resi...

The exchange of enthalpy and momentum at the air‐sea interface is an important process in tropical cyclone (TC) development and intensification, and the effects of sea spray have long been uncertain, particularly at high wind speeds. Here we use a coupled large‐eddy simulation and Lagrangian cloud model to run high‐resolution simulations of an idea...

Source functions for mechanically driven coarse-mode sea spray and dust aerosol particles span orders of magnitude owing to a combination of physical sensitivity in the system and large measurement uncertainty. Outside special idealized settings (such as wind tunnels), aerosol particle fluxes are largely inferred from a host of methods, including l...

The fate of migrating insects that encounter rainfall in flight is a critical consideration when modelling insect movement, but few field observations of this common phenomenon have ever been collected due to the logistical challenges of witnessing these encounters. Operational cloud radars have been deployed around the world by meteorological agen...

Source functions for mechanically driven coarse mode sea spray and dust aerosol particles span orders of magnitude owing to a combination of physical sensitivity in the system and large measurement uncertainty. Outside of special idealized settings (such as wind tunnels), aerosol particle fluxes are largely inferred from a host of methods, includin...

The Pi Chamber, located at Michigan Technological University, generates moist turbulent Rayleigh-B\'{e}nard flow in order to replicate steady-state cloud conditions. We take inspiration from this setup and consider a particle-laden, convectively-driven turbulent flow using direct numerical simulation (DNS). The aim of our study is to develop a simp...

The ubiquity of microplastics in marine environments is of growing concern and is increasingly receiving widespread attention. Due to the role of rivers and streams as suppliers of microplastics to the marine environment, it is essential to accurately capture their movements at these scales, but modeling and experimental knowledge in such settings...

To characterize energy resources and study of hydrodynamic effects induced by marine hydrokinetic devices in tidal channels, numerical models need to provide reliable representations of turbine arrays. In regions disconnected from the grid, near coastal protected areas and other relevant economic activities, there is a pressing need to evaluate the...

The Pi Chamber is a cloud chamber at Michigan Technological University that utilizes moist turbulent Rayleigh-Bénard flow between two temperature-controlled, saturated plates to create cloud conditions in a controlled laboratory setting. This experimental apparatus has been the source of numerous scientific studies but also offers an advantageous p...

A large-eddy simulation model is coupled with a Lagrangian cloud model to study marine fog. In this model, aerosols and droplets are treated from a Lagrangian frame of reference, in contrast to the traditional bulk and bin microphysical models. Droplet growth via condensation is governed by Köhler theory and environmental conditions local to the dr...

Over the past few years large-eddy simulation (LES) has demonstrated success in modelling continental radiation fog, and several recent studies have used LES to investigate the sensitivity of fog formation to physical processes such as turbulent mixing and surface heat and moisture exchange, as well as to the parametrization of microphysical proces...

We explore the role of gravitational settling on inertial particle concentrations in a wall-bounded turbulent flow. While it may be thought that settling can be ignored when the settling parameter Sv≡vs/uτ is small (vs is Stokes settling velocity, uτ is fluid friction velocity), we show that even in this regime the settling may make a leading order...

What is the most robust way to communicate flow trajectories? To answer this question, we employ two neural networks to respectively deconstruct (the encoder) and reconstruct (the decoder) trajectories, where information is passed between the two networks through a low-dimensional latent space in a set-up known as an autoencoder. To ensure that the...

Environmental supersaturation is a key parameter in the formation of fog and clouds, yet it cannot be measured directly and must be inferred. Calculating the ambient supersaturation in fog requires knowledge of the aerosol hygroscopicity as well as particle size distribution, and relatively few values have been reported in the literature. Here we u...

The LAgrangian Transport Eulerian Reaction Spatial (LATERS) Markov model was developed to predict upscaled bimolecular reactive transport in a flow around an array of solid cylinders. This method combines the stochastic Lagrangian Spatial Markov model (SMM) to predict transport and a volume averaged reaction rate equation to predict reactions of th...

We use theory and direct numerical simulations (DNSs) coupled with point particles to explore the average vertical velocities and spatial distributions of inertial particles settling in a wall-bounded turbulent flow. The theory is based on the exact phase-space equation for the probability density function describing particle positions and velociti...

Understanding momentum exchange at the air-sea interface is important for accurate hurricane predictions and understanding fundamental storm dynamics. One method for estimating air-sea momentum transfer in high winds is the flux-profile method, which infers surface momentum fluxes and the corresponding drag coefficient from mean velocity profiles o...

We explore the role of gravitational settling on inertial particle concentrations in a wall-bounded turbulent flow. While it may be thought that settling can be ignored when the Stokes settling velocity v s is small compared with the fluid friction velocity u τ , we show that even in this regime the settling may make a leading order contribution to...

Recently, advances in techniques for the detection of Lagrangian coherent structures (LCSs) have driven forward understanding of kinematics and particle transport in a variety of flows. One major shortcoming of these techniques, however, is the lack of an objective procedure for identifying time scales of interest, or an ability to characterize the...

In an effort to better represent aerosol transport in mesoscale and global‐scale models, large eddy simulations (LES) from the National Center for Atmospheric Research (NCAR) Turbulence with Particles (NTLP) code are used to develop a Markov chain random walk model that predicts aerosol particle profiles in a cloud‐free marine atmospheric boundary...

C-FOG is a comprehensive bi-national project dealing with the formation, persistence, and dissipation (life cycle) of fog in coastal areas (coastal fog) controlled by land, marine, and atmospheric processes. Given its inherent complexity, coastal-fog literature has mainly focused on case studies, and there is a continuing need for research that int...

C-FOG is a comprehensive bi-national project dealing with the formation, persistence, and dissipation (life cycle) of fog in coastal areas (coastal fog) controlled by land, marine, and atmospheric processes. Given its inherent complexity, coastal-fog literature has mainly focused on case studies, and there is a continuing need for research that int...

The authors wish to make the following corrections to this paper [...]

Quantifying the influence of sea spray on air‐sea fluxes under high‐wind conditions is challenging due to a variety of factors. Among existing models, the so‐called bulk air‐sea flux model is commonly used in meteorological applications due to its simplicity, which often involves strong but untested assumptions on spray‐mediated heat fluxes and fee...

Direct numerical simulations two-way coupled with inertial particles are used to investigate the particle distribution and two-way coupling mechanisms in turbulent open channel flow. In particular, the relationship between low- and high-inertia particles and the distinct large-scale motions (LSMs) and very-large-scale motions (VLSMs) which are char...

Effects of the computational domain size on inertial particle one-point statistics are presented for direct numerical simulations of turbulent open channel flow at a moderate Reynolds number, which are seeded with two-way coupled particles at low volume concentration (less than 1.5×10−3, for such particle load the one-way coupled particles scheme i...

In the previous study, Joyce et al. (Ocean Modelling, v. 141, 2019) develop a high resolution Advanced Circulation (ADCIRC)-based tide and storm surge model considering sea ice conditions. Therein, the effectiveness of using a parameterization of the skin and form drag over sea ice in surface wind stresses generating surge was examined. Such a para...

Tidal energy converter (TEC) arrays in tidal channels generate complex flow phenomena due to interactions with the local environment and among devices. Models with different resolutions are thus employed to study flows past TEC farms, which consider multiple spatial and temporal scales. Simulations over tidal cycles use mesoscale ocean circulation...

This study is concerned with the statistics of vertical turbulent channel flow laden with inertial particles for two different volume concentrations (ΦV=3×10−6 and ΦV=5×10−5) at a Stokes number of St+=58.6 based on viscous units. Two independent direct numerical simulation models utilizing the point-particle approach are compared to recent experime...

Direct numerical simulations two-way coupled with inertial particles are used to investigate the particle distribution and two-way coupling effect of low-inertia ($St_{LSM}=0.0625$, $St_{VLSM}=0.009$) and high-inertia ($St_{LSM}=0.475$, $St_{VLSM}=0.069$) particles associated with the large-scale motions (LSMs) and very-large-scale motions (VLSMs)...

Direct numerical simulations two-way coupled with inertial particles are used to investigate the particle distribution and two-way coupling effect of low-inertia ($St_{LSM}=0.0625$, $St_{VLSM}=0.009$) and high-inertia ($St_{LSM}=0.475$, $St_{VLSM}=0.069$) particles associated with the large-scale motions (LSMs) and very-large-scale motions (VLSMs)...

A common technique for estimating the sea surface generation functions of spray and aerosols is the so-called flux–profile method, where fixed-height concentration measurements are used to infer fluxes at the surface by assuming a form of the concentration profile. At its simplest, this method assumes a balance between spray emission and deposition...

Sea spray exchanging momentum, heat, and moisture is one of the major uncertainties in modeling air-sea surface heat fluxes under high wind speeds. Due to several untested assumptions in existing models and low fidelity in the measurements, questions regarding the appropriate methodology for modeling the effects of spray on air-sea fluxes still exi...

In this work, two independent direct numerical simulation models utilizing the point-particle approach are compared to recent experimental measurements, which is among the very few to directly address quantitative differences in a one-to-one comparison between measurements and simulations at matching conditions. We suggest that continued efforts ar...

Very-large-scale motions (VLSMs) and large-scale motions (LSMs) coexist at moderate Reynolds numbers in a very long open channel flow. Direct numerical simulations two-way coupled with inertial particles are analysed using spectral information to investigate the modulation of VLSMs. In the wall-normal direction, particle distributions (mean/prefere...

The exchange of surface and subsurface waters plays an important role in understanding and predicting large scale transport processes in streams and rivers. Accurately capturing the influence of small-scale features associated with turbulent dispersion on exchange in an upscaled framework is necessary for developing reliable predictive models at th...

Two-way coupled direct numerical simulations are used to investigate the effects of inertial particles on self-sustained, turbulent coherent structures (i.e. the so-called regeneration cycle) in plane Couette flow at low Reynolds number just above the onset of transition. Tests show two limiting behaviours with increasing particle inertia, similar...

In this work, we develop a novel Lagrangian model able to predict solute mixing in heterogeneous porous media. The Spatial Markov model has previously been used to predict effective mean conservative transport in flows through heterogeneous porous media. In predicting effective measures of mixing on larger scales, knowledge of only the mean transpo...

Very large-scale motions (VLSM) and large-scale motions (LSM) coexist at moderate Reynolds numbers (e.g. Re_tau=550,~950$) in a very long open channel flow. Direct numerical simulations two-way coupled with inertial particles are analysed using spectral information to investigate the modulation of VLSMs. Particle distributions show two layers corre...

Information about sea spray aerosol particle transport and their vertical distribution in the marine atmospheric boundary layer (MABL) is important in marine meteorological forecasting and geobiochemical models. However, due to difficulties in field observations, values of aerosol concentration are often limited to point measurements, and obtaining...

Two-way coupled direct numerical simulations are used to investigate the effects of inertial particles on self-sustained, turbulent coherent structures (i.e. the so-called the regeneration cycle) in plane Couette flow at low Reynolds number just above the onset of transition. Tests show two limiting behaviors with increasing particle inertia, simil...

In many atmospheric flows, a dispersed phase is actively suspended by turbulence, whose competition with gravitational settling ultimately dictates its vertical distribution. Examples of dispersed phases include snow, sea-spray droplets, dust, or sand, where individual elements of much larger density than the surrounding air are carried by turbulen...

Direct numerical simulation (DNS) combined with the Lagrangian point particle model is used to study Rayleigh-Bénard convection in order to understand modifications due to the interaction of inertial, nonisothermal particles with buoyancy-driven turbulence. In this system, turbulence can be altered through direct momentum coupling, as well as throu...

Information about the vertical distribution of sea spray aerosols in the marine atmospheric boundary layer (MABL) is important for large-scale weather and climate models in predicting reliable marine meteorological forecasting. Due to the difficulties of making field observations, measurements of spray aerosol concentrations are typically limited t...

Acceleration of an existing MPI-based, particle-laden turbulent flow simulation code is achieved using up to four NVIDIA GPU devices. The overall design is to transfer the entire flow velocity, temperature, and humidity fields to each device, and compute particle trajectories entirely on the GPU hardware. For one-way coupled turbulent flow simulati...

Previous studies have shown that sea spray droplets can play a significant role in air-sea heat and moisture exchange. The larger spray droplets have potential to transfer considerable amount of mass, momentum and heat, however they remain closer to surface and their residence times are shorter due to the faster settling. On the other hand, smaller...

Sea-spray droplets ejected into the marine atmospheric boundary layer take part in a series of complex transport processes. By capturing the air-droplet coupling and feedback, we focus on how droplets modify the total heat transfer across a turbulent boundary layer. We implement a high-resolution Eulerian–Lagrangian algorithm with varied droplet si...

The phenomenon of incomplete mixing reduces bulk effective reaction rates in reactive transport. Many existing models do not account for these effects, resulting in the overestimation of reaction rates in laboratory and field settings. To date, most studies on incomplete mixing have focused on diffusive systems; here, we extend these to explore the...

Direct numerical simulation (DNS) is used to simulate classic Rayleigh-Bénard convection between parallel plates, and La-grangian point particles two-way coupled in both momentum and temperature are added to investigate their modifications to turbulence and Nusselt number (Nu). The particles experience grav-itational settling, and are introduced at...

Recent progress in observations of wind fields by scanning aerosol lidar and motion estimation algorithms elevates interest in accuracy, precision , and resolution. Toward this, we are using large eddy simulations to advect a passive tracer in the model domain to mimic atmospheric aerosol. A wavelet-based optical flow algorithm is applied to the mo...

At the smallest scales of sediment transport in rivers, the coherent structures of the turbulent boundary layer constitute the fundamental mechanisms of bedload transport, locally increasing the instantaneous hydrodynamic forces acting on sediment particles, and mobilizing them downstream. Near the critical threshold for initiating sediment motion,...

Because the production, behavior, and life span of seawater droplets are complex, measuring and modeling them require a wide range of interdisciplinary techniques.

An analysis of the reliability of using dropsonde profile data to compute surface flux coefficients of momentum and heat is performed. Monin-Obukhov (MO) similarity theory forms the basis for the flux profile method, where mean profiles of momentum, temperature, and moisture are used to estimate surface fluxes, from which bulk flux coefficients can...

Direct numerical simulations are performed of turbulent planar Couette flow which are seeded with two-way coupled particles at low volume concentration. Based on an understanding of the development of particle stress (horizontal momentum carried vertically on average by the particle phase) in monodisperse systems at various particle Stokes numbers,...

Direct numerical simulations of an Eulerian-based carrier phase are performed which are two-way coupled in momentum and energy to Lagrangian droplets within a Boussinesq-type incompressible formulation, where the droplets are allowed to evaporate and condense and are thus coupled to the vapor field of the carrier phase. Turbulent planar Couette flo...

Direct numerical simulations of turbulent planar Cou-ette flow are performed with Lagrangian point particles chosen to represent noninteracting, two-way coupled particles in low volume concentration, moderate mass concentration systems. Specifically, the behavior of polydisperse mixtures of small particles in wall-bounded turbulent flow is examined...

Two-way coupled, particle-laden simulations are performed in turbulent Couette flow with the purpose of investigating the spectral extent of the particle influence on the turbulent energy cascade in wall-bounded flows. Direct numerical simulation of the carrier phase is performed in conjunction with the Lagrangian point-particle approximation for p...

Direct numerical simulations are combined with two-way coupled Lagrangian point particles to study the effect of Reynolds number on particle-turbulence interaction. Turbulent planar Couette flow is simulated at a constant dispersed phasemass loading of phi(m) = 0.25 for particle Stokes numbers of St(K) = [O(1), O(10), O(100)] (based on the Stokes t...

It has long been conjectured that spray ejected from the high-wind ocean surface enhances air/sea enthalpy fluxes, but a lack of observational data, particularly at wind speeds exceeding 20 ms-1, has prevented either confirmation or refutation of this hypothesis. The current study has two aims: first, to provide an estimate of surface enthalpy flux...

Direct numerical simulations (DNS) of turbulent Couette flow are combined with Lagrangian point-particle tracking to investigate the effects of a dispersed phase on bulk passive heat transport when the two phases can exchange both momentum and sensible heat. The idealized setup allows a fixed number of particles, without the influence of gravity, t...

A point-force model is used to study turbulent momentum transfer in the presence of moderate mass loadings of small (relative to Kolmogorov scales), dense (relative to the carrier phase density) particles. Turbulent Couette flow is simulated via direct numerical simulation, while individual particles are tracked as Lagrangian elements interacting w...

[1] Motivated by the possible effects of spray on the drag felt by the ocean surface in high winds, we use direct numerical simulation coupled with Lagrangian particle tracking to investigate how suspended inertial particles alter momentum flux in an idealized turbulent flow. Turbulent Couette flow is used for this purpose since the momentum flux p...

At , Newtonian flow past a circular cylinder exhibits a wake and detached shear layers which have transitioned to turbulence. It is the goal of the present study to investigate the effects which viscoelasticity has on this state and to identify the mechanisms responsible for wake stabilization. It is found through numerical simulations (employing t...

Using a code developed to compute high Reynolds number viscoelastic flows, polymer injection from the upstream stagnation point of a circular cylinder is modeled at Re = 3900. Polymer stresses are represented using the FENE-P constitutive equations. By increasing polymer injection rates within realistic ranges, significant near wake stabilization i...

We have created a robust numerical method for calculating fully three dimensional, time dependent non-Newtonian flows particularly where inertial forces are important. We have used our unstructured, finite-volume code to compute a wide variety of viscoelastic flows over a large range of Reynolds (Re) and Weissenberg (Wi) numbers. The method is base...

Using our three dimensional, time dependent finite volume code developed to compute non-Newtonian flows over a large range of Reynolds number (Re), we performed simulations of viscoelastic flow past a circular cylinder. Our focus was on elucidating elastic effects on transition to turbulence in the presence of viscoelasticity. The FENE-P constituti...

The results from a numerical investigation of inertial viscoelastic flow past a circular cylinder are presented which illustrate the significant effect that dilute concentrations of polymer additives have on complex flows. In particular, effects of polymer extensibility are studied as well as the role of viscoelasticity during three-dimensional cyl...

With the goal of creating a robust numerical method for simulating three dimensional, time dependent non-Newtonian flows, we have developed an unstructured, finite-volume code to compute a wide variety of viscoelastic flows over a large range of Reynolds (Re) and Weissenberg (Wi) numbers. Our method is based on the FENE-P constitutive model to desc...

The effect of initial microstructural deformation, alignment, and morphology on the response of wormlike micelle solutions in transient uniaxial extensional flows is investigated using a pre-shear device attached to a filament stretching rheometer. In filament stretching experiments, increasing the strength and the duration of the pre-shear just be...