A new computational study by Nahid Mirizadeh and Mohammad Manafpour, published in Results in Engineering, offers the most systematic answer yet. Using high-resolution computational fluid dynamics simulations in the open-source OpenFOAM platform, the researchers modeled a classical hydraulic jump at an upstream Froude number of 7.5, a regime typical of high-velocity spillway flows, while systematically varying the inflow air concentration from zero to fifty percent. Crucially, unlike most previous investigations, which examined only a handful of aeration levels, the study anchored every aerated scenario against a rigorously validated non-aerated baseline, allowing the progressive influence of air to be isolated and quantified for the first time across the full practical spectrum.

The numerical framework itself represents a careful exercise in verification. The team solved the unsteady Reynolds-averaged Navier-Stokes equations for a two-phase air-water mixture, tracking the free surface with the Volume of Fluid method, in which a scalar indicator function defines the fractional volume of water in each computational cell. Three turbulence closures were tested against laboratory measurements from the University of Queensland, where a horizontal rectangular flume 3.2 meters long, half a meter wide, and 0.41 meters high produced a well-defined jump with a Reynolds number near 140,000. The standard k-epsilon model emerged as the clear winner, predicting the roller length with only a 3.7 percent deviation from experiment, while the SST k-omega and Realizable k-epsilon models erred by 20 and 30 percent respectively.

Validation extended well beyond a single metric. The simulated free-surface profile matched laboratory data with a coefficient of determination of 0.99 and a Kling-Gupta Efficiency of 0.94, a score classified as excellent. The predicted secondary flow depth agreed with the theoretical Bélanger equation to within two percent, and velocity fields reproduced the characteristic structure of the jump: a high-velocity jet hugging the bed, a recirculating roller of reverse flow above it, and a shear layer between the two where turbulence is generated most intensely. A grid convergence analysis using the Grid Convergence Index confirmed that results were mesh-independent, with roller length varying by less than 2.5 percent between medium and fine grids.

With the model proven trustworthy, the researchers turned to the central question, and the answer they found is strikingly nonlinear. For aeration levels up to thirty percent, the free-surface profile of the jump barely budges, with normalized water depths changing by less than 1.5 percent. But at forty and fifty percent air concentration, the surface elevation at the beginning of the transition zone rises by roughly six to nine percent compared with the non-aerated case. The mechanism is physical rather than mysterious: the entrained air increases the volume of the air-water mixture and locally reduces its bulk density, forcing the flow to occupy a greater depth. For dam designers, this means that heavily aerated spillways may demand deeper tailwater to keep the jump anchored in its stilling basin.

The roller, the churning recirculation zone that gives the hydraulic jump its characteristic white-water appearance, responds even more dramatically. Low to moderate aeration of up to twenty percent lengthened the roller by 11.6 percent, but at forty and fifty percent aeration the roller stretched by 26.9 and 34.9 percent respectively. The authors attribute this elongation to two-phase flow mechanisms that slow the decay of turbulence: compressible air bubbles temporarily store turbulent energy and release it gradually, while buoyancy-driven secondary currents disrupt the main vortical structures. Because the mean streamwise velocity remains largely unchanged, the turbulence simply lingers longer, and the roller must extend downstream to complete the dissipation of kinetic energy. Since roller length often dictates the required basin length and the placement of baffle blocks, this finding carries direct consequences for structural design.

The most reassuring result concerns cavitation protection, the original motivation for pre-aeration in the first place. In the non-aerated simulation, the void fraction near the channel bed within the jump body remains essentially zero, leaving the boundary vulnerable to cavitation erosion. At forty and fifty percent inflow aeration, however, near-bed air concentrations reach approximately seven and twelve percent, with the higher value comfortably exceeding the eight percent threshold long associated with cavitation mitigation in the classic experimental literature. The study also confirms that peak air entrainment occurs in the initial portion of the shear layer, where the violent vortices at the jump toe drag air bubbles downward and transport them along the high-shear interface, in agreement with decades of experimental observation.

The velocity and turbulence fields reveal further subtleties. High aeration levels increased near-bed streamwise velocity by three to six percent, apparently because bubble penetration and slip effects reduce effective friction at the wall. While moderate, this change implies altered shear stresses that could shift scour patterns within and downstream of the stilling basin. Turbulent kinetic energy, meanwhile, peaked at the jump toe and concentrated in the shear layer, climbing by 18.3 percent at fifty percent aeration to reach approximately 2.76 square meters per second squared. Intriguingly, the normalized turbulence intensity first held steady, then rose sharply at thirty to forty percent aeration, and finally dropped at fifty percent, because the increase in maximum velocity outpaced the growth in turbulent fluctuations. The authors caution that RANS closures may underrepresent large-scale rotational eddies in highly aerated regions, suggesting that large-eddy simulation will be needed to fully resolve these structures.

Perhaps the most counterintuitive finding is what did not change: overall energy dissipation. Across the entire range of inflow air concentrations from zero to fifty percent, computed energy losses varied only between 63 and 64 percent, compared with 64.8 percent for the laboratory reference case. Because most of the entrained air is released downstream of the jump, the tailwater depth and velocity remain nearly identical to the non-aerated case, and the small residual differences stem mainly from variations in initial flow depth. This echoes earlier experimental work reporting less than two percent variation in dissipation between moderate aeration levels, and it means that pre-aeration delivers cavitation protection without sacrificing the jump’s core job of destroying excess kinetic energy.

Taken together, the results sketch a threshold-type picture of aerated hydraulic jumps that engineers can act on directly. Aeration up to twenty percent produces only minor hydraulic modifications, making it a low-cost, low-risk option. At forty percent and above, the benefits of robust cavitation protection arrive alongside measurable costs: deeper flow, rollers up to a third longer, higher near-bed velocities, and elevated turbulence that could increase dynamic loads on basin linings. The authors argue that these trade-offs should be explicitly built into tailwater calculations, basin dimensioning, and scour assessments for chute spillways and stilling basins operating at high Froude numbers. They also acknowledge the study’s limitations, including its reliance on RANS turbulence modeling, a two-dimensional idealization, and a single Froude number, and they call for future work spanning wider flow regimes, prototype-scale field validation, and design aids that translate these quantitative trends into practical engineering guidelines. For the dams that hold back the world’s rivers, even a few well-placed bubbles may prove to be the difference between a structure that endures and one that slowly crumbles.

Subject of Research: Effects of upstream flow aeration on two-phase hydraulic jump dynamics in rectangular channels using CFD simulation

Article Title: Progressive effects of upstream flow aeration on two-phase hydraulic jump dynamics in rectangular channels: a CFD investigation

Article References: Mirizadeh, N., & Manafpour, M. (2026). Progressive effects of upstream flow aeration on two-phase hydraulic jump dynamics in rectangular channels: a CFD investigation. Results in Engineering, 32, Article 113234. https://doi.org/10.1016/j.rineng.2026.113234

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113234

Keywords: hydraulic jump, CFD, OpenFOAM, pre-aeration, cavitation, stilling basin, spillway, two-phase flow, Volume of Fluid, turbulence, roller length, energy dissipation

The research, carried out by Baptiste Moreau, Alfonso Caiazzo, Thomas Amon, Long Chen and David Janke, set out to evaluate an open-source lattice Boltzmann solver called OpenLB against the established finite volume solver OpenFOAM. Conventional computational fluid dynamics tools used in agriculture solve the Navier–Stokes equations with finite volume or finite element methods, approaches that have been extensively validated over decades and are embedded in mature commercial and open-source packages. Their weakness is computational cost: as turbulence develops and domains grow, simulations can run for hours or days, which makes them poorly suited to applications where predictions are needed quickly, such as interpreting data streaming from barn-integrated sensor networks.

The lattice Boltzmann method takes a fundamentally different route to the same physics. Instead of discretizing the Navier–Stokes equations directly, it evolves a pseudo-compressible formulation on a fixed Cartesian lattice, tracking population densities that represent particles moving along a discrete set of velocities, commonly nineteen directions in three dimensions, the so-called D3Q19 model. Each time step consists of a collision step, in which the densities relax toward an equilibrium distribution described by the Bhatnagar–Gross–Krook operator, and a propagation step, in which information moves to neighboring nodes. The crucial property is locality: the collision step, which carries most of the computational burden, depends only on values at a single lattice node. Combined with a structured grid and explicit time-stepping, this makes the method exceptionally well suited to massive parallelization on modern hardware, including graphics processing units.

To test whether this promise holds for agricultural flows, the team built a benchmark that others can easily reproduce. They used a 1:100 scaled model of a typical agricultural building, 0.25 meters wide and 0.13 meters high, mounted perpendicular to the flow in the atmospheric boundary layer wind tunnel at the ATB Potsdam. The model, originally part of a dairy farm study, was elevated on a smooth table to minimize the influence of the tunnel’s thick boundary layer, producing an inflow with a nearly constant vertical velocity and turbulence profile. With the barn height as the characteristic length and an inlet velocity of 13 meters per second, the flow reached a Reynolds number of roughly 114,000, firmly in the turbulent regime. Velocity measurements were collected along fourteen vertical sample lines upstream and downstream of the model.

On the computational side, the barn geometry was supplied as an STL file and embedded in a domain about three meters long, 0.98 meters high and two meters wide. OpenLB generates a uniform lattice whose spacing is set by a refinement parameter, which the researchers varied from coarse grids of about 115,000 cells to finely resolved lattices exceeding 50 million cells. No-slip conditions on the ground and barn surfaces were enforced with a second-order interpolation scheme due to Bouzidi, a uniform inlet velocity was ramped up smoothly to suppress nonphysical oscillations, and slip conditions closed the top and sides. Turbulence was handled with the Smagorinsky large-eddy subgrid model, implemented in the lattice Boltzmann framework by adding an eddy viscosity to the relaxation time, with a Smagorinsky constant of 0.15 chosen after a preliminary sensitivity study.

The accuracy assessment compared time-averaged velocity components against the wind tunnel data using a battery of error metrics, including mean relative error, mean absolute error, root mean square error and a symmetric mean absolute percentage error. For the streamwise velocity, the simulation reproduced the qualitative trends of the experimental profiles along essentially all sampling lines, and about half of all measurement points showed relative errors below 13 percent. In regions dominated by the interaction with the building, such as lines immediately beside and behind the barn, agreement was partly very good, with errors below 5 percent. Larger deviations appeared for the vertical velocity component just upstream of the model, where the solver underestimated the measurements, possibly because a single constant Smagorinsky coefficient overestimates turbulent viscosity in the nearly turbulence-free inflow. The authors note that dynamic subgrid models and local grid refinement could improve these regions, and they emphasize that the achieved accuracy is consistent with previous validation studies of open-source solvers against comparable wind tunnel data.

The efficiency results are where the study becomes striking. Measured in million lattice updates per second, the CPU-based parallelization sustained roughly 100 MLUPs on refined meshes with 20 cores, at the upper end of values reported in the literature, and showed strong scaling with per-processor throughput declining only from 6.2 to 5.0 as core counts grew. Against OpenFOAM on the same grid, the lattice Boltzmann solver was about 23 times faster when both used 40 CPU cores, delivering a time ratio of 27 compared with 620 for the finite volume solver. The finite volume code’s scalability also broke down beyond roughly 35 cores, whereas OpenLB continued to benefit from additional processors. Moving to the server’s NVIDIA A100 GPUs brought a further speedup of about a factor of ten over MPI, reaching nearly 2,500 MLUPs on the finest meshes, a performance in line with the best lattice Boltzmann implementations reported elsewhere.

Combining these effects, the validated benchmark case achieved an overall acceleration of approximately 46-fold relative to the OpenFOAM reference, while for the most refined case examined, about 22 million cells, the combined CPU and GPU gains suggest a potential speedup approaching 230-fold, a figure the authors present as an indication of scalability rather than a validated result. True real-time simulation, where computation keeps pace with simulated time, was not achieved: GPU runs showed time ratios between 10 and 100. Even so, the researchers point out that multiple GPUs could close much of the remaining gap, and that the approach is already accessible far beyond supercomputing centers, since graphics cards with around 6,000 CUDA cores suitable for such computations are available for roughly 600 euros, raising the prospect of transient airflow simulations on a standard laptop.

The authors are careful to delineate the limits of their findings. The benchmark used a closed building, a nearly uniform inflow profile and an incompressible turbulent flow on a structured Cartesian lattice, precisely the class of problems for which the lattice Boltzmann method is best suited. More realistic scenarios involving internal ventilation, complex geometries, turbulent approaching flows or strongly coupled transport processes may show smaller efficiency gains and require case-by-case evaluation. A key constraint of the current solver version is its multi-block approach, which does not yet support local grid refinement, forcing uniform fine resolution across the entire domain and straining GPU memory in multiscale problems; a forthcoming release with local refinement is expected to be assessed in future work. Nevertheless, the study concludes that the open-source framework delivers accuracy comparable to established finite volume solvers at a fraction of the computational cost, positioning lattice Boltzmann methods as a credible foundation for the fast, transient dispersion simulations needed to quantify and mitigate emissions from naturally ventilated livestock buildings.

Subject of Research: Performance assessment of an open-source lattice Boltzmann framework for accelerated turbulent airflow simulation around agricultural buildings

Article Title: Accelerating airflow simulations for agricultural applications: Performance assessment of an open-source lattice Boltzmann framework

Article References: Moreau, B., Caiazzo, A., Amon, T., Chen, L., & Janke, D. (2026). Accelerating airflow simulations for agricultural applications: Performance assessment of an open-source lattice Boltzmann framework. Results in Engineering, 32, Article 112822. https://doi.org/10.1016/j.rineng.2026.112822

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.112822

Keywords: lattice Boltzmann method, OpenLB, computational fluid dynamics, livestock housing, natural ventilation, GPU computing, OpenFOAM, turbulence modeling, wind tunnel validation, agricultural emissions, high performance computing, near-real-time simulation