Turbulent Transport Research Articles

The universal instability in optimised stellarators

In tokamaks and neoclassically optimised stellarators, like Wendelstein 7-X (W7-X) and the Helically Symmetric Experiment, turbulent transport is expected to be the dominant transport mechanism. Among the electrostatic instabilities that drive turbulence, the trapped-electron mode (TEM) has been shown both analytically and in simulations to be absent over large ranges of parameter space in quasi-isodynamic stellarator configurations with the maximum-$J$property. It has been proposed that the reduction of the linear TEM growth rate in such configurations may lead to the passing-electron-driven universal instability, which is often subdominant to the TEM, becoming the fastest-growing instability over some range of parameter space. Here, we show through gyrokinetic simulations using theGenecode, that the universal instability is dominant in a variety of stellarator geometries over a range of parameter space typically occupied by the TEM, but most consequentially in devices which possess beneficial TEM stability properties like W7-X, which locally satisfies the maximum-$J$property for deeply trapped particles in the regions of worst curvature. We find that the universal instability exists at long perpendicular wavelengths and, as a result, dominates the potential fluctuation amplitude in nonlinear simulations. In W7-X, universal modes are found to differ in parallel mode structure from trapped-particle modes, which may impact turbulence localisation in experiments.

The sensitivity of a mid-latitude maritime stratocumulus cloud to surface fluxes

Surface fluxes of stratocumulus clouds over mid-latitude oceans have larger variability and bigger Bowen ratios than those over subtropical oceans. This study investigates how mid-latitude maritime stratocumulus clouds respond to surface fluxes and what the underlying mechanisms are. A closed-cellular stratocumulus cloud over mid-latitude North Pacific Ocean is simulated with large eddy simulation. A control case and a reduced-flux case (with surface fluxes 50% reduced) are compared. Liquid water path (LWP) and turbulent kinetic energy (TKE) decrease as surface fluxes are reduced. It is revealed that reducing surface fluxes leads to a cooler and drier boundary layer, which directly leads to a higher cloud base. The weaker turbulence near the cloud top leads to less entrainment, resulting in a lower cloud top. Therefore, the cloud is 21% thinner with a smaller LWP in the reduced-flux case. Quadrant analysis shows that TKE production processes including surface heating, in-cloud latent heating, and cloud-top evaporative cooling are all weaker in the reduced-flux case. Meanwhile, cloud-top entrainment heating and overshooting of air parcels into the inversion, as TKE consumption processes, are also weaker in the reduced-flux case. These TKE production and consumption processes counteract with each other, leading to quite different pictures of turbulence transport in the two cases. In the subcloud layer, the control case is dominated by surface heating (indicating a turbulent heating effect), while the reduced-flux case is dominated by evaporative cooling in the downdraft region (indicating a turbulent cooling effect). In the cloud layer, the difference of heat flux between the two cases is mainly due to the difference in latent heating. At cloud top, the two cases have similar heat flux.

Linear and non-linear properties of the Goldreich–Schubert–Fricke instability in stellar interiors with arbitrary local radial and latitudinal differential rotation

ABSTRACT We investigate the linear and non-linear properties of the Goldreich–Schubert–Fricke (GSF) instability in stellar radiative zones with arbitrary local (radial and latitudinal) differential rotation. This instability may lead to turbulence that contributes to the redistribution of angular momentum and chemical composition in stars. In our local Boussinesq model, we investigate varying the orientation of the shear with respect to the ‘effective gravity’, which we describe using the angle ϕ. We first perform an axisymmetric linear analysis to explore the effects of varying ϕ on the local stability of arbitrary differential rotations. We then explore the non-linear hydrodynamical evolution in three dimensions using a modified shearing box. The model exhibits both diffusive GSF instability and a non-diffusive instability that occurs when the Solberg-Høiland criteria are violated. We observe the non-linear development of strong zonal jets (‘layering’ in the angular momentum) with a preferred orientation in both cases, which can considerably enhance turbulent transport. By varying ϕ, we find instability with mixed radial and latitudinal shears transports angular momentum more efficiently (particularly if adiabatically unstable) than cases with purely radial shear (ϕ = 0). By exploring the dependence on box size, we find the transport properties of the GSF instability to be largely insensitive to this, implying we can meaningfully extrapolate our results to stars. However, there is no preferred length-scale for adiabatic instability, which therefore exhibits strong box-size dependence. These instabilities may contribute to the missing angular momentum transport required in red giant and subgiant stars and drive turbulence in the solar tachocline.

The distribution of accretion rates as a diagnostic of protoplanetary disc evolution

ABSTRACT We show that the distribution of observed accretion rates is a powerful diagnostic of protoplanetary disc physics. Accretion due to turbulent (‘viscous’) transport of angular momentum results in a fundamentally different distribution of accretion rates than accretion driven by magnetized disc winds. We find that a homogeneous sample of ≳300 observed accretion rates would be sufficient to distinguish between these two mechanisms of disc accretion at high confidence, even for pessimistic assumptions. Current samples of T Tauri star accretion rates are not this large, and also suffer from significant inhomogeneity, so both viscous and wind-driven models are broadly consistent with the existing observations. If accretion is viscous, the observed accretion rates require low rates of disc photoevaporation (≲10−9 M⊙ yr−1). Uniform, homogeneous surveys of stellar accretion rates can therefore provide a clear answer to the long-standing question of how protoplanetary discs accrete.

Analysis of turbulent mixing in a methane–oxygen recessed injector for space propulsion

Turbulent mixing in a methane–oxygen recessed injector is studied using direct numerical simulations. The operating point is chosen to be fuel-rich and at high pressure to recreate a representative environment for space propulsion applications. The results are used to investigate the transport of the turbulent mixture fraction statistics and the validity of conventional transport models. It is observed that molecular diffusion is only relevant near the boundary layer of the injection recess cavity and at the recirculation zone. Moreover, turbulent mixing in the axial direction is negligible as radial turbulent diffusion dominates. Radial turbulent diffusion near injection is driven by Kelvin–Helmholtz Instabilities (KHI) manifesting at large scales in the order of the injector geometry. The dominance of this process over microscale mixing originates negative turbulent diffusion, which produces a mixture resegregation and the appearance of lean pockets far from the oxidizer injection plane. Gradient models display poor capabilities for the prediction of this sort of phenomena. Closure models for the turbulent mixing transport terms are proposed and evaluated. An anisotropic gradient model is devised, providing performance improvements within the recess cavity and the recirculation region. In addition, a novel filtered Reynolds-averaged Navier Stokes approach based on the mixing state is proposed. This new methodology shows excellent prediction capabilities in the regions dominated by KHI, accurately predicting negative turbulent diffusivity. The challenges associated with this model are commented on, and strategies to enable its application are proposed.

Global gyrokinetic simulation for toroidal impurity mode turbulence

In this study, global gyrokinetic simulations of the toroidal impurity mode (tIM) turbulence are performed. A linear analysis shows that the tIM is an instability that occurs in the bad curvature region when the density gradients of bulk ions and impurities are in opposite directions. The tIM can be unstable even when the temperature profiles are flat. In the presence of temperature gradients, the tIM and toroidal ion temperature gradient (tITG) mode could coexist. For the small temperature gradient, the tIM is found to be dominant. The tIM turbulence drives the large inward impurity and outward ion particle transports. Furthermore, the inward ion heat flux driven by the tIM turbulence causes the ion temperature profile to be more peaked than the initial one. For the large temperature gradient, while such inward ion heat flux does not occur because of the dominant tITG mode, the large inward impurity and outward ion particle fluxes are still observed due to the subdominant tIM. These results indicate that the tIM plays an important role in turbulent heat and particle transport when impurities are injected.

Characterization of mesoscopic turbulent transport events with long-radial-range correlation in DIII-D H-mode plasmas

A dimensionless collisionality scan has been performed in H-mode plasmas on DIII-D tokamak, with detailed measurements of intermediate-to-high wavenumber turbulence using Doppler backscattering systems. It is found that the shorter wavelength turbulence develops into spatially asymmetric turbulent structures with a long-radial-range correlation (LRRC) in the mid-radius region of high collisionality discharges. Linear cgyro simulations indicate that the underlying turbulence is likely driven by the electron-temperature-gradient mode. The LRRC transport events are highly intermittent and show a power spectrum of Sñ(k⊥)∝k⊥−1 for density fluctuations, which is often associated with self-organized criticality. The magnitude and the radial scale of those turbulent structures increase significantly when the Er×B mean flow shearing rate decreases at higher collisionality. The enhanced LRRC transport events appear to be correlated with the degraded energy confinement time. The emergence of such LRRC transport events may serve as a candidate explanation for the degrading nature of H-mode core plasma confinement at high collisionality.

Theoretical analysis of unsteady buoyant turbulent heat and mass transport from a vertical plate using LRN k-ϵ model

The contemporary analysis has been developed to investigate the transient natural convective combined heat and mass transport of a turbulent flow adjacent to the plate by utilizing the low Reynolds number (LRN) k-ϵ model. The research problem on turbulent flow is assumed to be two dimensional and viscous incompressible. The governing turbulent equations such as continuity, momentum, energy, concentration, turbulent kinetic energy (TKE) and dissipation rate of TKE are considered as per the flow geometry. Due to the non-availability of analytical or direct numerical techniques, the corresponding highly nonlinear PDE’s are solved by adopting the standard implicit type of finite difference method namely Crank–Nicolson scheme. Also, this scheme is unconditionally stable and helps to keep the governing turbulent flow equations in discretized form and are solved via tridiagonal matrix algorithm. The simulated results for several control parameters including turbulent Reynolds number are graphically displayed and also analyzed the flow profiles. To understand the physical phenomenon of turbulent flow, the authors shown the turbulent behavior of average momentum, energy and mass transfer rates. It has been noted that, the average temperature and concentration fields boosted with rising values of . Also, TKE and dissipation rate of TKE profiles increase with enhancing turbulent values. In addition, the simulated turbulent flow results from the LRN k-ϵ model are compared with usual laminar flows as a special case and found to be in respectable agreement.

Complexity of carbon dioxide flux in urban areas: A comparison with natural surfaces

The characteristics of turbulent CO2 transport and its dissimilarity with heat and water vapor are investigated over both natural and urban areas. A novel index TS is proposed to effectively quantify the transport similarity between two scalars. By comparison, it is found that the transport of CO2 shows great complexity in urban areas. It is ideal in natural areas that heat, water vapor, and CO2 are efficiently transported by thermal plumes (i.e., the dominant coherent structures under unstable conditions), and that the transport similarity among them becomes increasingly evident with the increase of atmospheric instability. However, in urban areas, the transport of CO2 shows significant dissimilarity from that of heat and water vapor, and it is hard to detect the role of thermal plumes. Furthermore, it is observed that the sector-average CO2 flux in urban areas changes largely with the wind blowing from different urban functional areas. Specially, for a given direction, there might be contrasting characteristics in CO2 transport under different unstable conditions. These features can be explained by the flux footprint. Since the CO2 sources and sinks are distributed heterogeneously in urban areas, the variation of footprint areas with wind direction or atmospheric instability, causes the alternation between source-dominated (i.e., upward) and sink-dominated (i.e., downward) CO2 transport. Therefore, the role of coherent structures in CO2 transport is substantially confused by spatially-confined sources/sinks in urban areas, leading to significant transport dissimilarity between CO2 and heat or water vapor and thus the great complexity in CO2 transport. The findings in this study are helpful to promote the understanding of the global carbon cycle in depth.

A Parallel Computational–Statistical Framework for Simulation of Turbulence: Applications to Data-Driven Fractional Modeling

In this work, an open-source computational–statistical platform to obtain synthetic homogeneous isotropic turbulent flow and passive scalar transport is presented. A parallel implementation of the well-known pseudo-spectral method in addition to the comprehensive record of the statistical and small-scale quantities of the turbulent transport are offered for executing on distributed memory CPU-based supercomputers. The user-friendly workflow and easy-to-run design of the developed package are disclosed through an extensive and step-by-step example. The resulting low- and high-order statistical records vividly verify a well-established and fully developed turbulent state as well as the seamless statistical balance of conservation laws. The post-processing tools provided in this platform would allow the user to easily construct multiple important transport quantities from primitive turbulent fields. The programming codes for this tool are accessible through GitHub (see Data Availability Statement).

High-resolution simulations of a turbulent boundary layer impacting two obstacles in tandem

We created a new publicly available data set of high-fidelity numerical simulations for two obstacles in tandem invested by a fully resolved turbulent boundary layer. In the three configurations of skimming flow, wake interference, and isolated roughness, we identify the regions of intense turbulent fluctuations, production and transport of turbulent kinetic energy, and examine the anisotropy-invariants map.

Non-Equilibrium Turbulent Transport in Convective Plumes Obtained from Closure Theory

The non-equilibrium property of turbulence modifies the characteristics of turbulent transport. With the aid of response function formalism, such non-equilibrium effects in turbulent transport can be represented by the temporal variation of the turbulent energy (K) and its dissipation rate (ε) along the mean stream through the advective derivatives of K and ε. Applications of this effect to the turbulent convection with plumes are considered for the first time in this work. The non-equilibrium transport effects associated with plumes are addressed in two aspects. Firstly, the effect associated with a single plume is evaluated using data measured in the recent plume/jet experiments. The second argument is developed for the collective turbulent transport associated with multiple plumes mimicking the stellar convection zone. In this second case, for the purpose of capturing the plume motions into the advective derivatives, use has to be made of the time–space double-averaging procedure, where the turbulent fluctuations are divided into the coherent or dispersion component (which represents plume motions) and the incoherent or random component. With the aid of the transport equations of the coherent velocity stress and the incoherent counterpart, the interaction between the dispersion and random fluctuations are also discussed in the context of convective turbulent flows with plumes. It is shown from these analyses that the non-equilibrium effect associated with plume motions is of a great deal of relevance in the convective turbulence modeling.

Scalar transport in flow past finite circular patches of tall roughness

Simultaneous particle image velocimetry-planar laser-induced fluorescence (PIV-PLIF) measurements are conducted on the flow around and downstream of patches of tall cylinders with various solidity ϕ≡Nc(d/D)2, where Nc is the number of cylinders in a patch, d and D are the diameters of the cylinder and the patch, respectively. Results suggest that the bleeding and scalar concentration in the wake and above the patches are dependent upon ϕ. Recirculation bubble appears at downstream of the patch boundary, limiting the flow from convecting downstream and forcing it (and the scalar) to escape vertically from the top of the patch. Above the wake, a shear layer generated by the velocity difference between the free flow and the wake itself shields the near-wake region. The net effect of the solidity on the wake topology is the appearance of an elongated patch as ϕ decreases and a taller patch as ϕ increases. In terms of scalar transport, both advective and turbulent vertical scalar transport are enhanced as ϕ increases. High advective vertical scalar transport CV is concentrated around the canopy (above the canopy due to vertical bleeding and at the TE due to high scalar concentration), while high turbulent transport c′v′¯ largely coincides with the shear layer. Octant analysis of the conditionally averaged fluctuating components (u′, v′, and c′) shows an enhanced mixing inside the shear layer and entrainment of turbulent flows between the shear layer, the wake region below and the freestream above this layer. In terms of eddy diffusivity models, the complexity of the eddy diffusivity constant increases with ϕ.

Post-dynamical inspiral phase of common envelope evolution

After the companion dynamically plunges through the primary’s envelope, the two cores remain surrounded by a common envelope and the decrease of the orbital period Porb stalls. The subsequent evolution has never been systematically explored with multidimensional simulations. For this study, we performed 3D hydrodynamical simulations of an envelope evolving under the influence of a central binary star using an adaptively refined spherical grid. We followed the evolution over hundreds of orbits of the central binary to characterize the transport of angular momentum by advection, gravitational torques, turbulence, and viscosity. We find that local advective torques from the mean flow and Reynolds stresses associated with the turbulent flow dominate the angular momentum transport, which occurs outward in a disk-like structure about the orbital plane and inward along the polar axis. Turbulent transport is less efficient, but can locally significantly damp or enhance the net angular momentum radial transport and may even reverse its direction. Short-term variability in the envelope is remarkably similar to circumbinary disks, including the formation and destruction of lump-like overdensities, which enhance mass accretion and contribute to the outward transport of eccentricity generated in the vicinity of the binary. If the accretion onto the binary is allowed, the orbital decay timescale settles to a nearly constant value τb ∼ 103 to 104 Porb, while preventing accretion leads to a slowly increasing τb ∼ 105 Porb at the end of our simulations. Our results suggest that the post-dynamical orbital contraction and envelope ejection will slowly continue while the binary is surrounded by gas and that τb is often much shorter than the thermal timescale of the envelope.

What Controlled the Low-Level Moisture Transport during the Extreme Precipitation in Henan Province of China in July 2021?

Abstract A record-breaking precipitation event occurred in the Henan province of China in July 2021 (217HP). To identify the moisture source of the event, ensemble experiments with 120 members were conducted in this study. Results show that the precipitable water during this extreme event was primarily contributed by the low-level southeasterly (LLSE) water vapor transport. The LLSE was largely enhanced by the pressure gradient force maintained by the western Pacific subtropical high and further amplified by the latent heat release in the rainfall system over Henan. The positive moisture advection by the LLSE and evaporative water occurred below 950 hPa and was redistributed into higher levels by the LLSE jet-enhanced subgrid vertical turbulent transport. As a result, the combination of the enhanced LLSE centered around 950 hPa and the increase of moisture below 850 hPa were the main drivers for the continuous strengthening of LLSE moisture transport, with the former playing the dominant role. It is also found that not only the presence but also the intensity of the LLSE jet were important for reproducing the extreme rainfall. The impact of binary tropical cyclones In-Fa and Cempaka on the low-level moisture transport was also examined. We found that In-Fa (2021) presented an uncertain impact on 217HP, while Cempaka (2021) was found to be unfavorable for 217HP. Different from the LLSE water vapor transport, Cempaka mainly acted to weaken the southwesterly wind to the southwest of Henan by reducing the pressure gradient and impeding the water vapor transport toward Henan.

Dynamic Subgrid Turbulence Modeling for Shallow Cumulus Convection Simulations beyond LES Resolutions

Abstract A scale-dependent dynamic Smagorinsky model is implemented in the Met Office/NERC Cloud (MONC) model using two averaging flavors, along Lagrangian pathlines and local moving averages. The dynamic approaches were compared against the conventional Smagorinsky–Lilly scheme in simulating the diurnal cycle of shallow cumulus convection. The simulations spanned from the LES to the near-gray-zone and gray-zone resolutions and revealed the adaptability of the dynamic model across the scales and different stability regimes. The dynamic model can produce a scale- and stability-dependent profile of the subfilter turbulence length scale across the chosen resolution range. At gray-zone resolutions the adaptive length scales can better represent the early precloud boundary layer leading to temperature and moisture profiles closer to the LES compared to the standard Smagorinsky. As a result, the initialization and general representation of the cloud field in the dynamic model is in good agreement with the LES. In contrast, the standard Smagorinsky produces a less well-mixed boundary layer, which fails to ventilate moisture from the boundary layer, resulting in the delayed spinup of the cloud layer. Moreover, strong downgradient diffusion controls the turbulent transport of scalars in the cloud layer. However, the dynamic approaches rely on the resolved field to account for nonlocal transports, leading to overenergetic structures when the boundary layer is fully developed and the Lagrangian model is used. Introducing the local averaging version of the model or adopting a new Lagrangian time scale provides stronger dissipation without significantly affecting model behavior.

Fast transport simulations with higher-fidelity surrogate models for ITER

A fast and accurate turbulence transport model based on quasilinear gyrokinetics is developed. The model consists of a set of neural networks trained on a bespoke quasilinear GENE dataset, with a saturation rule calibrated to dedicated nonlinear simulations. The resultant neural network is approximately eight orders of magnitude faster than the original GENE quasilinear calculations. ITER predictions with the new model project a fusion gain in line with ITER targets. While the dataset is currently limited to the ITER baseline regime, this approach illustrates a pathway to develop reduced-order turbulence models both faster and more accurate than the current state-of-the-art.

Thermospheric Temperature and ΣO/N2 Variations as Observed by GOLD and Compared to MSIS and WACCM‐X Simulations During 2019–2020 at Deep Solar Minimum

AbstractThe ultraviolet‐imaging spectrograph that comprises Global‐scale Observations of the Limb and Disk (GOLD) mission in geostationary orbit at 47.5°W longitude has taken full disk images at high cadence throughout the deep solar minimum period of 2019–2020. Synoptic (i.e., concurrent and spatially unified and resolved) observations of thermospheric temperature and composition at ∼150 km altitude are made for the first time, allowing GOLD to disambiguate temporal and spatial variations. Here we analyze the daytime effective temperature and column integrated O and N2 density ratio (ΣO/N2) data simultaneously observed by GOLD over 120°W–20°E longitude and 60°S–60°N latitude from 13 October 2019 to 12 October 2020. Daily zonal mean values are calculated for each latitude and compared with NRLMSIS 2.0 and simulations from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X). On average, the GOLD observations show higher temperatures than Mass Spectrometer Incoherent Scatter radar (MSIS) and WACCM‐X by ∼20–60 K (5%–10%) and 80–120 K (12%–18%), respectively. The ΣO/N2 ratios observed by GOLD are larger than the MSIS results by ∼0.4 (40%) but smaller than the WACCM‐X simulations by ∼0.3 (30%). The observed and modeled results are correlated at most latitudes (r = 0.4–0.8), and GOLD, MSIS, and WACCM‐X all display a similar seasonal variation and change with latitude. WACCM‐X simulates a larger annual variation in ΣO/N2, suggesting that the thermospheric circulation is overestimated and atmospheric waves and turbulence transport are not properly represented in the model.

The turbulence development of a vertical natural convection boundary layer

Results from direct numerical simulations of a vertical natural convection boundary layer (NCBL) with $Pr=0.71$ reveal that the turbulence development of such a thermally driven convective flow has two distinct stages: at relatively low Grashof number, the bulk flow is turbulent while the near-wall region is laminar-like or weakly turbulent; at sufficiently high Grashof number, the entire flow becomes turbulent in the sense of von Kármán (cf. Grossmann & Lohse, J. Fluid Mech., vol. 407, 2000, pp. 27–56, for the ultimate turbulent regime). Investigations on the turbulence statistics show that the near-wall Reynolds shear stress is negligible in the weakly turbulent regime but will grow in magnitude as the flow transitions to the ultimate regime at higher Grashof number. Similar behaviour is also seen in the streamwise turbulence intensity, where it develops from a mono-peak profile into a dual-peak structure as the Grashof number increases. At higher Grashof number, the near-wall energetic site is shown to have an energy distribution similar to that of a canonical wall-bounded turbulence (e.g. Hutchins & Marusic, Phil. Trans. R. Soc.A, vol. 365, 2007, pp. 647–664), with a peak centred at fixed location and wavelength ( $y^+=18$ and $\lambda ^+_x=1000$ ) in viscous coordinates. Investigation on the spanwise spectra also suggests that the turbulent near-wall streaks emerge only at sufficiently high Grashof number, with constant spacing $\lambda _z^+\approx 130$ . The extent of the weakly turbulent regime is identified using the maximum velocity location $\delta_m$ and a laminar length scale $\delta_u$ . The development of near-wall turbulence is also investigated by examining the turbulence kinetic energy budget. In the weakly turbulent regime, the near-wall turbulence is sustained predominantly by the pressure transport in addition to the shear production. At higher Grashof number, the flow becomes fully turbulent, and both turbulent transport and shear production become stronger, while the pressure transport is decreased. These results also reveal that the production–dissipation ratio $P/\varepsilon$ of the NCBL would follow a fundamentally different trend to the canonical wall-bounded flows, which further supports that the near-wall turbulence generation is affected by the bulk flow.

Features of turbulence during wildland fires in forested and grassland environments

Fire-induced turbulence and the feedback into the fire, following ambient changes, differ for forested (sub-canopy) and grassland environments. Here, we synthesize observations from multiple experimental surface fires: two sub-canopy backing fires, one sub-canopy heading fire, and a grassland heading fire. We identify and compare the most essential coherent structures and processes of each case from the turbulent momentum fluxes and turbulent kinetic energy (TKE) budget terms. In the sub-canopy burns, turbulent eddies are strongest near the canopy top: high streamwise turbulent flux accompanies low cross-stream turbulent flux and vice versa. In the grassland fire, both streamwise and cross-stream eddies strengthen simultaneously until a certain height, informing a vertical length scale for the fire-influence. Moreover, the forward sweep from streamwise eddies assists in the fire spread by pushing hot gases towards unburnt fuel. In the sub-canopy fires, shear production and buoyancy production are more substantial near the canopy top for more intense fires, while their magnitudes decrease with decreasing fire intensity. At mid-canopy-height scales, buoyancy production dominates shear production, becoming the key mechanism for vertical transport of TKE. In the grassland fire, shear production dominates buoyancy production near the surface and is insignificant beyond a certain height relative to the flame length, while buoyancy production increases with height, becoming substantial further away from the surface. Turbulent transport terms are also active in both environments. For intense sub-canopy fires, there is a loss in TKE due to its expulsion to the boundary layer aloft via the transport term, compensated by a reversal process: TKE influx via the transport term. In the grassland fire, the transport term mimics this behavior until a certain height. The insights into the relative significance of the respective turbulent fluxes and TKE budget terms in each environment can help simplify the complex system of equations governing fire physics.