The violent hydrodynamic impact in water entry is a well-known phenomenon. Various methods have been applied to mitigate this “destructive force.” We experimentally investigate a method for reducing the impact force of water entry, which uses a gas jet to impinge on the liquid surface prior to the object entry. The blowing of the gas jet flow forms a cavity in the water and the penetration of the object into the water is thus less impactful. This method also significantly alters the flow field structure in the impact region, resulting in a reduction of the added fluid mass, the counterthrust of the gas jet that can further attenuate the impact intensity. We reported four cavity regimes and six impact modes formed in the gas-liquid interaction for a range of the modified Froude numbers. In particular, the regime of jet cavity only has a jet-assisted water entry with almost no impact event, and the maximum reduction in impact acceleration can reach nearly 90% with the reduction in entry velocity being about 10% relative to the impact without gas jet. The impact force reduction mechanism is considered to be a combination of the reduction of the added fluid mass and the presence of gas jet momentum.

This paper presents a study on the effectiveness of two turbulence models, the large eddy simulation (LES) model and the k-ε turbulence model, in predicting mixing time within a ladle furnace using the computational fluid dynamics (CFD) technique. The CFD model was developed based on a downscaled water ladle from an industrial ladle. Corresponding experiments were conducted to provide insights into the flow field, which were used for the validation of CFD simulations. The correlation between the flow structure and turbulence kinetic energy in relation to mixing time was investigated. Flow field results indicated that both turbulence models aligned well with time-averaged velocity data from the experiments. However, the LES model not only offered a closer match in magnitude but also provided a more detailed representation of turbulence eddies. With respect to predicting mixing time, increased flow rates resulted in extended mixing times in both turbulence models. However, the LES model consistently projected longer mixing times due to its capability to capture a more intricate distribution of turbulence eddies.

Ladle metallurgy serves as a crucial component of the steelmaking industry, where it plays a pivotal role in manipulating the molten steel to exercise precise control over its composition and properties. Turbulence in ladle metallurgy influences various important aspects of the steelmaking process, including mixing and distribution of additives, alongside the transport and removal of inclusions within the ladle. Consequently, gaining a clear understanding of the stirred flow field holds the potential of optimizing ladle design, improving control strategies, and enhancing the overall efficiency and steel quality. In this project, an advanced Particle-Tracking-Velocimetry system known as “Shake-the-Box” is implemented on a cylindrical water ladle model while compressed air injections through two circular plugs positioned at the bottom of the model are employed to actively stir the flow. To mitigate the particle images distortion caused by the cylindrical plexi-glass walls, the method of refractive matching is utilized with an outer polygon tank filled with a sodium iodide solution. The volumetric flow measurement is achieved on a 6 × 6 × 2 cm domain between the two plugs inside the cylindrical container while the flow rate of gas injection is set from 0.1 to 0.4 L per minute. The volumetric flow field result suggests double gas injection at low flow rate (0.1 L per minute) produce the least disturbed flow while highly disturbed and turbulent flow can be created at higher flow rate of gas injection.

This study employs an integrated approach, combining three-dimensional flow visualization and two-dimensional flow measurement to investigate the underlying unsteady aerodynamic mechanisms of hovering hawkmoths. Using a single vortex ring model, three aerodynamic force components, such as aerodynamic force induced by unsteady circulation, vortex loop size variation and added mass, are estimated within a dimensionless time (normalized by one wing beat cycle) range of 0.418 < T ^* < 0.455, where both the vortex loop circulation and loop size data are available. The force analysis reveals that the unsteady circulation-induced aerodynamic force dominates the overall force production and contributes 67% of the total force while the vortex loop size variation and added mass effect-induced aerodynamic forces only count for 25% and 8%, respectively. These findings suggest the hawkmoth primarily relies on unsteady circulation to generate aerodynamic forces.