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Bioreactors can perform biochemical conversions mediated by biocatalysts, such as enzymes, animal cells, plants, and microorganisms. Among several existing models, airlift bioreactors are devices with the low shear environment and good mass transfer with low energy consumption, employed in several biochemical processes. The fluid flow is enabled through air injection by the sparger located at the bioreactor base. Despite its simple geometry compared with the conventional bioreactors, airlift performance can be optimized via geometrical modifications. Therefore, the objective of this work was to evaluate the effects of the addition of helical flow promoters, positioned in the riser and/or downcomer regions of an airlift of concentric tubes measuring the volumetric oxygen coefficient (kLa) and gas holdup. The results obtained by varying the gas flow rate from 1.0 to 4.0 vvm allowed the system evaluation of oxygen transfer and gas holdup. The inclusion of helical flow promoters increased the kLa, reaching up to 23% in oxygen transfer compared to tests without helicoids and up to 14% increase in the gas holdup. The inclusion of helical flow promotors was beneficial for all gas flow rates. Thus, including these flow promoters is an effective strategy to increase the oxygen transfer rate for bioprocess optimization.

The initial space settings of suitable environments for plants strongly affect the mutual feedback evolution of the river landscape and terrestrial plants. Thus, based on the morphological characteristics of newly-defined systematic out-branching channels in nature, this study performs an effective simulation of the flow of a designed moderately curved bend with a single short branch. The practice-based channel curvatures and branch on-off conditions are controlled in ANSYS FLUENT. The results show that: (1) the core zone of the depth-averaged primary velocity excess is approximately inversely equivalent to the channel migration potential; (2) the existence of the branch can strongly promote the formation of a new core vorticity zone and the conflicting development of the inner-negative and outer-positive vorticity zone after the bifurcation site at the cross-sections; (3) the free-flowing branch can greatly diminish the downstream helical flow strength; overall, the variation tendency of the ratio of helical flow strength to discharge squared is immune to the small range of change in stable inflow; and (4) the downstream channel is a strongly erosive region with the branch outlet closed, judging by the shear stress distribution; otherwise, it is a deposition region. The findings lay the groundwork for harmonious optimization of branch and plant configurations in river-bend systems.

We explored here the case of three-dimensional non-stationary flows of helical type for the incompressible couple stress fluid with given Bernoulli-function in the whole space (the Cauchy problem). In our presentation, the case of non-stationary helical flows with constant coefficient of proportionality α between velocity and the curl field of flow is investigated. In the given analysis for this given type of couple stress fluid flows, an absolutely novel class of exact solutions in theoretical hydrodynamics is illuminated. Conditions for the existence of the exact solution for the aforementioned type of flows were obtained, for which non-stationary helical flow with invariant Bernoulli-function satisfying to the Laplace equation was considered. The spatial and time-dependent parts of the pressure field of the fluid flow should be determined via Bernoulli-function if components of the velocity of the flow are already obtained. Analytical and numerical findings are outlined, including outstanding graphical presentations of various types of constructed solutions, in order to elucidate dynamic snapshots that show the timely development of the topological behavior of said solutions.

The work and life of Ippolit Stepanovich Gromeka is reviewed. Gromeka authored a classical set of eleven papers on fluid dynamics in just ten years before a tragic illness ended his life. Sadly, he is not well known to the western scientific community because all his publications were written in Russian. He is one of the three authors who independently derived an analytical solution for accelerating laminar pipe flow. He was the first to eliminate the contradiction between the theories of Young and Laplace on capillary phenomena. He initiated the theoretical basis of helical (Beltrami) flow, and he studied the movement of cyclones and anticyclones seventeen years before Zermelo (whose work is considered as pioneering). He is also the first to analyse wave propagation in liquid-filled hoses, thereby including fluid–structure interaction.

Helical axial-flow multiphase (HAFM) pumps experience intermittent gas-blocking events, which negatively impact performance and threaten the stability of the overall pump and pipeline systems. This study applies jet flow field method to HAFM pumps. Active intervention in the gas-liquid separation process, utilizing external energy, results in the reorganization of the flow field within HAFM pumps. The effect of jet location on improving the efficiency of HAFM pumps is assessed, with a focus on the active flow control mechanism through jet influence. The study indicates that the region sensitive to jet site distribution affecting pump performance is 0.5Lc≤ xr ≤ 0.7Lc, while the weakly sensitive region is 0.15Lc ≤ xr ≤ 0.5Lc. When xr ≤ 0.15Lc, the improvement in head and efficiency under high gas content conditions is reduced. Jet flow field control technology obviously decreases the gas phase accumulation in the downstream flow channel of the moving blade cascade. The optimal position for reducing gas phase agglomeration in the impeller channel is 0.3Lc. The jet site arrangement significantly affects the pressure structure near the cascade trailing edge. Appropriate jet hole positioning significantly improves the pressure structure at the cascade trailing edge, decreases reflux caused by separation vortices at the impeller outlet, and enhances the hydraulic performance in the multiphase pump.

The performance of pump-jet propulsion systems is critically important in defense and marine applications. However, their optimization has encountered bottlenecks due to a lack of theoretical understanding of underlying flow mechanisms. This study investigates the influence of the pump cavity gap on the flow characteristics and performance of a helical mixed-flow pump using numerical simulations. The gap size is non-dimensionalized as a gap coefficient—defined as the ratio of pump cavity gap to blade thickness—with the inlet ring gap fixed at 0.2 mm. Results demonstrate that the gap coefficient significantly affects internal flow stability and energy loss. A gap coefficient of 0.15 effectively suppresses leakage and vortex formation, improving efficiency (peak efficiency reaches 75%) and head (1.9 m) under low-flow conditions. This configuration also promotes uniform pressure distribution on the impeller shaft surface and reduces turbulent kinetic energy and axial vorticity. In contrast, a smaller gap coefficient (0.125) exacerbates flow separation at high flow rates, while a larger value (0.2) increases leakage losses and degrades performance. The study elucidates correlations between the pump cavity gap and vortex evolution, pressure gradient, and turbulence distribution, providing theoretical support for the optimized design of helical mixed-flow pumps.

Because the helical axial flow gas-liquid mixing pump has the great advantage of conveying gas-liquid two-phase mixed medium, it has become the main core equipment for deep-sea oil and natural gas exploitation. The gas phase aggregation and bubble movement trajectory in the impeller channel have been widely studied, but the increase of medium flow resistance caused by flow separation has not been deeply discussed. Combined with the Euler multiphase flow model and the SST k-ω turbulence model, the numerical calculation of the helical axial flow gas-liquid mixed pump is carried out. Under design flow conditions Q = 100 m3/h, head H = 30 m, speed n = 4500 r/min, specific speed ns =213.6 r/min, and under different inlet gas content conditions, the influence of the bionic waveform leading edge blade on drag reduction characteristics of the helical axial flow gas-liquid mixed pump was investigated. By designing the blade with a leading-edge structure with different heights and pitches, the separation of the mixed medium and the suction surface is effectively suppressed, and the flow resistance of the medium in the 1/10 area of the inlet end of the blade is reduced. The results show that when the height A is 0.25%L and the pitch λ is 12.5%h, the maximum drag reduction rate in this region is 52.6%, the maximum increase in efficiency of the mixed pump is 2.2%, and the maximum increase in head is 4.8%. This study can provide technical support for flow drag reduction in gas-liquid mixed pump.

Background—Physiological helical flow in the ascending aorta has been well documented in the last two decades, accompanied by discussions on possible physiological benefits of such axial swirl. Recent 4D-MRI studies on healthy volunteers have found indications of early generation of helical flow, early in the systole and close to the valve plane. Objectives—Firstly, the aim of the study is to investigate the hypothesis of premature swirl existence in the ventricular outflow tract leading to helical flow in the valve plane, and second to investigate the possible impact of two different mechanical valve designs on the preservation of this early helical flow and its subsequent hemodynamic consequences. Methods—We use a pulse duplicator with an aortic arch and High-Speed Particle Image Velocimetry to document the flow evolution in the systolic cycle. The pulse-duplicator is modified with a swirl-generating insert to generate early helical flow in the valve plane. Special focus is paid to the interaction of such helical flow with different designs of mechanical prosthetic heart valves, comparing a classical bileaflet mechanical heart valve, the St. Jude Medical Regent valve (SJM Regent BMHV), with the Triflo trileaflet mechanical heart valve T2B version (Triflo TMHV). Results—When the swirl-generator is inserted, a vortex is generated in the core flow, demonstrating early helical flow in the valve plane, similar to the observations reported in the recent 4D-MRI study taken for comparison. For the Triflo trileaflet valve, the early helical flow is not obstructed in the central orifice, similar as in the case of the natural valve. Conservation of angular momentum leads to radial expansion of the core flow and flattening of the axial flow profile downstream in the arch. Furthermore, the early helical flow helps to overcome separation at the outer and inner curvature. In contrast, the two parallel leaflets for the bileaflet valve impose a flow straightener effect, annihilating the angular momentum, which has a negative impact on kinetic energy of the flow. Conclusion—The results imply better hemodynamics for the Triflo trileaflet valve based on hydrodynamic arguments under the discussed hypothesis. In addition, it makes the Triflo valve a better candidate for valve replacements in patients with a pathological generation of nonaxial velocity in the ventricle outflow tract.

The embryonic outflow tract (OFT) eventually undergoes aorticopulmonary septation to form the aorta and pulmonary artery, and it is hypothesized that blood flow mechanical forces guide this process. We performed detailed studies of the geometry, wall motions, and fluid dynamics of the HH25 chick embryonic OFT just before septation, using noninvasive 4D high-frequency ultrasound and computational flow simulations. The OFT exhibited expansion and contraction waves propagating from proximal to distal end, with periods of luminal collapse at locations of the two endocardial cushions. This, combined with periods of reversed flow, resulted in the OFT cushions experiencing wall shear stresses (WSS or flow drag forces) with elevated oscillatory characteristics, which could be important to signal for further development of cushions into valves and septum. Furthermore, the OFT exhibits interesting double-helical flow during systole, where a pair of helical flow structures twisted about each other from the proximal to distal end. This coincided with the location of the future aorticopulmonary septum, which also twisted from the proximal to distal end, suggesting that this flow pattern may be guiding OFT septation.

Pulsating flows through tubular geometries are laminar provided that velocities are moderate. This in particular is also believed to apply to cardiovascular flows where inertial forces are typically too low to sustain turbulence. On the other hand, flow instabilities and fluctuating shear stresses are held responsible for a variety of cardiovascular diseases. Here we report a nonlinear instability mechanism for pulsating pipe flow that gives rise to bursts of turbulence at low flow rates. Geometrical distortions of small, yet finite, amplitude are found to excite a state consisting of helical vortices during flow deceleration. The resulting flow pattern grows rapidly in magnitude, breaks down into turbulence, and eventually returns to laminar when the flow accelerates. This scenario causes shear stress fluctuations and flow reversal during each pulsation cycle. Such unsteady conditions can adversely affect blood vessels and have been shown to promote inflammation and dysfunction of the shear stress-sensitive endothelial cell layer.