Jean-Pierre Hickey

University of Waterloo | UWaterloo · Department of Mechanical and Mechatronics Engineering

A novel approach to identify internal interfacial layers, or IILs, in wall-bounded turbulent flows is proposed. Using a fuzzy cluster method (FCM) on the streamwise velocity component, a unique and unambiguous grouping of the uniform momentum zones (UMZs) is achieved, thus allowing the identification of the IILs. The approach overcomes some of the...

We address our long-standing claim that vortex reconnection is one of the dominant sources of aeroacoustic noise in a number of canonical turbulent flows. The reconnection of two antiparallel vortices is studied via direct numerical simulation of the compressible Navier-Stokes equations in order to fully resolve the acoustic noise generation and fa...

Transpiration cooling in a turbulent boundary layer on a flat plate is investigated using direct numerical simulations (DNS). The simulations are performed by solving the compressible Navier-Stokes equations at low Mach number conditions (M_inf = 0.3). Both the coolant and the hot gas are air, with isothermal walls and coolant at a temperature of T...

The problem of scaling the near-wall mean velocity profiles of turbulent flows and collapsing them with the law of the wall has been traditionally studied using the conservation of momentum, by employing various levels of assumptions. In the van Driest transformation (“Turbulent Boundary Layer in Compressible Fluids,” Journal of the Aeronautical Sc...

The goal of this research is to study the thermoacoustic response of diffusion flames due to their relevance in applications such as rocket engines. An in-house code is extended to solve the fully compressible counterflow diffusion flame equations, allowing for a spatially- and temporally-varying pressure field. Various hydrogen-air flames with a r...

Krypton is an open-source framework to solve the linear and non-linear Parabolized Stability Equations (PSE) on a curvilinear coordinate system as a predictive tool to estimate the laminarto- turbulent transition at transonic conditions. Written in Python and leveraging well-established libraries, the framework includes a laminar flow solver using...

Traditional Riemann solvers fall into two broad categories: exact solvers, which require multiple iterations to achieve high accuracy, and approximate linearized solvers, which achieve fast runtime at the expense of reduced accuracy. Here we explore learning-based Riemann solvers, termed FluxNets, as a new approach that balances accuracy and comput...

The group combustion characteristics of core–shell nanothermite particles differ from other dispersed solid or liquid fuels. In a core–shell structure, each discrete nanothermite particle can undergo an exothermic reaction as the oxygen atoms in the metal oxide shell undergo a solid state diffusion to oxidize the metal core. This feature allows the...

The wave structure of approximate Riemann solvers has a significant impact on the accuracy and computational requirements of finite volume codes. We propose a class of structurally complete approximate Riemann solvers (StARS) and provide an efficient means for analytically restoring the expansion wave to pre-existing three-wave solvers. The method...

Passive acoustic aircraft and wake localization methods rely on the noise emission from aircraft and their wakes for detection, tracking, and characterization. This paper takes a holistic approach to passive acoustic methods and first presents a systematic bibliographic review of aeroacoustic noise of aircraft and drones, followed by a summary of s...

We study the effect of temperature-dependent viscosity on the preferential concentration of bidispersed, externally-heated solid particles in decaying isotropic turbulence via direct numerical simulations (DNS). More specifically, we investigate the role of liquid- and gas-like viscosity–which respectively decrease and increase with temperature–on...

Ignitable micro- and nano-sized energetic particles are desirable in MEMS (micro-electromechanical system) devices in delivering energy to a target and producing heat in-situ. It is challenging however to fabricate these particles due to the incomplete mixing between the fuel and oxidizer during the manufacturing process and its sensitivity to exte...

We study the sound generation mechanism of initially subsonic viscous vortex reconnection at vortex Reynolds number Re (≡ circulation/kinematic viscosity) = 1500 through decomposition of Lighthill's acoustic source term. The Laplacian of the kinetic energy, flexion product, enstrophy and deviation from the isentropic condition provide the dominant...

A conceptual model for targeted particle delivery is proposed using controlled vortex ring reconnection. Entrained particles can be efficiently transported within the core of vortex rings which advect via self-induction. A pair of these particle-transporting vortex rings traveling in the streamwise direction along parallel trajectories will mutuall...

We assess Reynolds-averaged Navier–Stokes (RANS) turbulent closures for the prediction of a turbulent boundary layer with transpiration cooling via comparison with a high-fidelity direct numerical simulation database. This study considers the canonical zero-pressure gradient, flat-plate, turbulent boundary layer over a massively cooled wall, with t...

View Video Presentation: https://doi.org/10.2514/6.2021-2605.vid Transpiration cooling is an active thermal protective system (TPS) increasingly used in space applications under high thermal loads. A coolant gas is effused through a porous wall into a turbulent boundary layer (TBL) via a pressure gradient. The pressure fluctuations at the wall abov...

Physical conservation laws are inherently Lagrangian. However, analyses in fluid mechanics using the Lagrangian framework are often forgone in favor of those using the Eulerian framework. This is perhaps due to a lack of experimental techniques with high temporal and spatial resolution that track the movement of fluid tracers in a flow domain. The...

A deep-learning based approach is developed for efficient evaluation of thermophysical properties in numerical simulation of complex real-fluid flows. The work enables a significant improvement of computational efficiency by replacing direct calculation of the equation of state with a deep feedforward neural network with appropriate boundary inform...

A continuum-scale model for the combustion of consolidated nanothermite pellets is introduced. A simplified chemical kinetics model is used for the solid state nanothermite reaction while a two-phase porous media flow accounts for the mass and heat transfer within the consolidated pellet under an equilibrium thermodynamic assumption. The thermophys...

A turbulent/non-turbulent interface detection method is proposed based on fuzzy clustering of the instantaneous streamwise velocity field. The fuzzy cluster method overcomes the limitations of standard detection methods by removing the user bias in thresholding and window selection and not relying on the calculation of mean flow properties. The rob...

The predictive capabilities of near-wall turbulence modeling at high-speed, non-adiabatic flow conditions are assessed for commercial and open-source computational fluid dynamic (CFD) solvers. This work investigates the following solvers: OpenFOAM (open-source), SU2 (open-source), Star-CCM+ (commercial), and Fluent (commercial). A turbulent flat pl...

A conceptual model for targeted particle delivery is proposed using controlled vortex ring reconnection. Entrained particles can be efficiently transported within the core of the vortex ring which is propelled via self-induction. A pair of these particle-transporting vortices travelling in the streamwise direction along parallel trajectories will m...

The single-phase instability of high-pressure, steady, laminar counterflow diffusion flame is studied using the Vapor–Liquid Equilibrium (VLE) theory. The a posteriori study focuses on the identification of the potentially unstable regions emerging throughout the full combustion states represented by the high-pressure counterflow diffusion flame so...

A semi-empirical estimate of the time-averaged thickness of a planar shock embedded in a turbulent mean flow is presented in an effort to quantify the characteristic time and length scales for turbulence modeling. Simplified Favre-averaged Navier-Stokes equations are reformulated and combined with the Rankine-Hugoniot relations to obtain an equatio...

We present analytical solutions to the stationary normal shock and centred rarefaction waves, which are valid for arbitrary non-ideal equations of state (EOS). Generalized shock functions are defined which are shown to be well-behaved and locally convex, facilitating rapid and exact computation of shock ratios. For rarefactions, a novel domain mapp...

Inductively-heated solid particles dispersed within a decaying isotropic turbulent carrier gas are investigated via Direct Numerical Simulations (DNS). The multiphase simulations account for the compressibility and temperature-dependent viscosity effects of the carrier gas. We develop a semi-empirical model for solid particle heating through hyster...

Transpiration cooling in a turbulent boundary layer on a flat plate is simulated using direct numerical simulations (DNS). The simulations are performed by solving the compressible Navier-Stokes equations at low Mach number conditions (M ∞ = 0.3). Both the coolant and the hot gas are air, with isothermal walls and coolant at a temperature of T w /T...

Shock-vector control is a promising technology for low-to-medium sized space launch vehicles. In this work, we report numerical results from Enhanced Delayed Detached Eddy Simulations conducted in a typical shock-vector control working environment. Overall, the results agree well with analytical predictions obtained from a previously developed low-...

A targeted turbulent flow control strategy, based on selective heating of streamwise-aligned heat strips, is assessed for drag reduction using direct numerical simulations of variable viscosity and compressible turbulent channel flows. As increasing the temperature of a gas increases its viscosity, heating is generally an unfavorable drag mitigatio...

Bidimensional empirical mode decomposition (BEMD) is an empirical method to decompose fluctuating signals into various intrinsic mode functions (IMF); these represent different scales of the turbulent fluctuations. The scale separation flow permits an analysis of their respective contributions towards the overall skin friction of the turbulent boun...

A one-dimensional analytical model is proposed to account for mixing and compute the indirect noise in compound nozzle flows. The model is based on the work of Morton et al. (Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 234 (1196), 1956, 1–23) and serves as an extension to Younes & Hickey (Journal of Sound and...

We report on a transitional, high-resolution direct numerical simulation of a temporally developing planar asymmetric wake at Re = 4000 based on the mass flux deficit. The asymmetric wake is formed by a Blasius and a fully turbulent boundary layer on either side of an infinitely thin splitter plate. Such a setup has direct relevance in low-Reynolds...

The computational challenges in turbulent combustion simulations stem from the physical complexities and multi-scale nature of the problem which make it intractable to compute scale-resolving simulations. For most engineering applications, the large scale separation between the flame (typically sub-millimeter scale) and the characteristic turbulent...

The increased modeling complexity needed to simulate high-pressure combustion in rocket engines results in significant computational costs-costs which are not always justified for engineering applications. Multicomponent diffusion computations are at least 40% more expensive than the constant Lewis number diffusion assumption for the simplest hydro...

A turbulent boundary layer is an essential flow case of fundamental and applied fluid mechanics. However, accurate measurements of turbulent boundary layer parameters (e.g., friction velocity $u_\tau$ and wall shear $\tau_w$), are challenging, especially for high speed flows (Smits et al., 2011). Many direct and/or indirect diagnostic techniques ha...

The outer region of fully developed turbulent boundary layers can be viewed as a collection of uniform momentum zones separated by thin (but finite-thickness) shear layers referred to as momentum internal interface layers (MIILs). We first show the existence of such interfacial layers under transcritical thermodynamic conditions and introduce their...

We explore the noise generation mechanisms in the compressible vortex reconnection of two anti-parallel vor-tices of equal strength via a high-order DNS of the fully compressible Navier-Stokes equations. Over a range of vortex Reynolds number (1500-12,000, where Re = circu-lation/viscosity), we show that noise generation occurs in the reconnection...

The effect of surface roughness on the stability characteristics at transonic conditions is investigated using the parabolized stability equations (PSE). The PSE numerical framework is formulated in curvilinear coordinates and the base flow is computed directly from the laminar compressible Navier-Stokes equations. The effect of surface roughness i...

Many propulsion devices such as liquid rocket engines and gas turbines operate under transcritical or supercritical conditions, where the real fluid properties must be taken into account to model the thermodynamic non-idealities and transport anomalies. The use of such complex non-ideal state equations is prohibitively expensive and can account for...

We study the boundary-layer turbulence and freestream turbulence interface (BTFTI), the turbulent spot and freestream turbulence interface (TSFTI), and the laminar boundary-layer and freestream turbulence interface (LBFTI) using direct simulation. Grid spacings in the freestream are less than 1 Kolmogorov length scale during transition. Probability...

A systematic deficiency of current turbulence models which are based on the Reynolds-averaged Navier-Stokes equations (RANS) is their inability to correctly predict the interaction of turbulence with shocks. This is because RANS models do not account for the unsteady motion or fragmentation of the shock wave within the interaction zone. Typically,...

A novel approach to identify internal interfacial layers, or IILs, in wall-bounded turbulent flows is proposed. Using a Fuzzy Cluster Method (FCM) on the streamwise velocity component, a unique and unambiguous grouping of the Uniform Momentum Zones is achieved, thus allowing the identification of the IILs. The approach overcomes some of the key lim...

Fully-developed, turbulent boundary layers are characterized by zones of uniform momentum which are delineated by internal interfacial layers (IIL). The uniform momentum zones (UMZ) have been shown to be related to the underlying coherent structures in wall-bounded turbulence. A novel IIL identification method, proposed by Duosi et al., allows the...

A novel approach to identify internal interfacial layers, or IILs, in wall-bounded turbulent flows is proposed. Using a Fuzzy Cluster Method (FCM) on the streamwise velocity component, a unique and unambiguous grouping of the Uniform Momentum Zones is achieved, thus allowing the identification of the IILs. The approach overcomes some of the key lim...

In this study, we evaluate the thermodynamic structure of laminar hydrogen/oxygen flames at supercrit- ical pressures using 1D flame calculations and large-eddy simulation (LES) results. We find that the real fluid mixing behavior differs between inert (cold flow) and reactive (hot flow) conditions. Specifically, we show that combustion under trans...

A flamelet-based combustion model is proposed for the prediction of wall heat transfer in rocket engines and confined combustion systems. To account for convective heat loss due to the interaction of the flame with the wall, a permeable thermal boundary condition is introduced in the counterflow diffusion flame configuration. The solution of the re...

Experimental shock wave boundary layer interactions (SBLI) at a compression corner of a flat plate model with deflectable flap and variable surface temperature were studied in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR) at Mach 7.4 and \({6.65\times 10^6}\,{\text {m}^{-1}}\) unit Reynolds number. The present...

We have performed direct numerical simulations (DNS) of compressible turbulent channel flow at supercritical pressure with top and bottom isothermal walls kept respectively at a supercritical (Ttop > Tpb) and subcritical temperature (Tbot < Tpb), where Tpb is the pseudoboiling temperature. The DNS are conducted using a high-order discretization of...

Significance Uncovering the constitutive coherent structure in the inner layer of the canonical turbulent boundary layer has remained a central fluid mechanics theme, because it tests our intellectual ability to understand even the simplest external flow. We describe here how turbulent spots are initiated in bypass boundary-layer transition and unc...

An efficient tabulation strategy for turbulent combustion simulations is proposed. Using a locally adaptive arrangement of structured Bézier patches-often used in computer graphics-the combustion manifold can be efficiently tabulated; thus reducing the table size by over an order of magnitude while maintaining high accuracy. A hybrid search algorit...

An extension to the classical FPV model is developed for transcritical real-fluid combustion simulations in the context of finite volume, fully compressible, explicit solvers. A double-flux model is developed for transcritical flows to eliminate the spurious pressure oscillations. A hybrid scheme with entropy-stable flux correction is formulated to...

A systematic deficiency of current turbulence models which are based on the Reynolds averaged Navier-Stokes equations (RANS) is their inability to correctly predict the interaction of turbulence with shocks. This is because RANS models do not account for the unsteady motion or fragmentation of the shock wave within the interaction zone. Typically,...

An accurate prediction of the performance characteristics of cavitating cryogenic turbopump inducers is essential for an increased reliance on numerical simulations in the early turbopump design stages of liquid rocket engines. This work focuses on the sensitivities related to the choice of turbulence models on the cavitation prediction in flow set...

Summary. Experimental shock wave boundary layer interactions (SBLI) at an unswept compression corner of a flat plate model with deflectable flap and variable surface temperature were studied in the DLR High Enthalpy Shock Tunnel Goettingen (HEG) at Mach 7.4 and 6.4e6 1/m unit Reynolds number. The present paper focuses on the effect of the leading...

Robust turbulence modelling of cavitating flows in cryogenic turbopump inducers is essential for accurate prediction of their performance characteristics and increased reliance on numerical simulations during their early design stages. This work focuses on (1) the sensitivities related to the choice of turbulence models on the cavitation prediction...

The compressibility effects on the structural evolution of the transitional high-speed planar wake are studied. The relative Mach number ( $Ma_{r}$ ) of the laminar base flow modifies two fundamental features of planar wake transition: (i) the characteristic length scale defined by the most unstable linear mode; and (ii) the domain of influence o...

The vortex breakdown of the rib structures was studied through fully resolved, temporal direct numerical simulations for an initial relative Mach number. The vector field around the stagnation point of these breakdown events supports the theoretical foundation of the vortex breakdown. Using critical point theory, that an outwardly spiraling vortex...

Grid fins provide good maneuverability to missiles in supersonic flow because they can maintain lift at a higher angle of attack. Although static aerodynamic data exist, very little quantitative dynamic performance information is available for grid fin controlled missiles. The high drag associated with grid fins is also a concern. Dynamic simulatio...

Grid fins have found different applications over the last three decades, from control surfaces in missiles and projectiles to emergency brakes and stabilization devices in space vehicles. Particularly, lattice fins provide a higher maneuverability to agile high-speed mis-siles in supersonicflow due to their capacity to maintain lift at higher angle...