Aeration Levels Research Articles

Kinematics and dynamics of green water on a fixed platform in a large wave basin in focusing wave and random wave conditions

Green water kinematics and dynamics due to wave impingements on a simplified geometry, fixed platform were experimentally investigated in a large, deep-water wave basin. Both plane focusing waves and random waves were employed in the generation of green water. The focusing wave condition was designed to create two consecutive plunging breaking waves with one impinging on the frontal vertical wall of the fixed platform, referred as wall impingement, and the other directly impinging on the deck surface, referred as deck impingement. The random wave condition was generated using the JONSWAP spectrum with a significant wave height approximately equal to the freeboard. A total of 179 green water events were collected in the random wave condition. By examining the green water events in random waves, three different flow types are categorized: collapse of overtopping wave, fall of bulk water, and breaking wave crest. The aerated flow velocity was measured using bubble image velocimetry, while the void fraction was measured using fiber optic reflectometry. For the plane focusing wave condition, measurements of impact pressure were synchronized with the flow velocity and void fraction measurements. The relationship between the peak pressures and the pressure rise times is examined. For the high-intensity impact in the deck impingement events, the peak pressures are observed to be proportional to the aeration levels. The maximum horizontal velocities in the green water events in random waves are well represented by the lognormal distribution. Ritter’s solution is shown to quantitatively describe the green water velocity distributions under both the focusing wave condition and the random wave condition. A prediction equation for green water velocity distribution under random waves is proposed.

EVALUATION OF FRANCIS TURBINE AERATION AS A MEASURE TO ATTENUATE PRESSURE PULSATIONS

When operating in off-design conditions, Francis Hydraulic Turbines features flow phenomena related with low-frequency pressure pulsations. Those pulsations mechanisms can lead the system to resonance or instabilities. In this situation, high-pressure pulsations can cause structural or mechanical components failure, wear by cavitation, besides reducing energy generation quality. Inserting air into the draft tube is one of the most common measure to mitigate pressure pulsations. In this panorama, the present work aim to apply a one-dimensional distributed parameter mathematical model of the hydraulic circuit of a Francis turbine in order to predict full load instability. The Vortex hydroacoustic parameters are computed by CFD simulations. In order to verify the model, and evaluate aeration effectiveness, a design of a mechanical device that can control the axial atmospheric aeration valve to enable tests in a turbine prototype is developed. Further, field tests shows that a discharge of air of 1.3% of the rated discharge can reduce pressure pulsations by 90% in a specific full load operating point. Also, in this case study applied to ITAIPU turbines, the mathematical modelling result has successfully predict full load instability observed in field test under variation of aeration level. Keywords: Francis turbine, Aeration, Hydraulic Instability, CFD.

A novel fuzzy-logic control strategy minimizing N2O emissions

A novel control strategy for achieving low N2O emissions and low effluent NH4+ concentration is here proposed. The control strategy uses the measurements of ammonium and nitrate concentrations in inlet and outlet of the aerobic zone of a wastewater treatment plant to calculate a ratio indicating the balance among the microbial groups. More specifically, the ratio will indicate if there is a complete nitrification. In case nitrification is not complete, the controller will adjust the aeration level of the plant in order to inhibit the production of N2O from AOB and HB denitrification. The controller was implemented using the fuzzy logic approach. It was comprehensively tested for different model structures and different sets of model parameters with regards to its ability of mitigating N2O emissions for future applications in real wastewater treatment plants. It is concluded that the control strategy is useful for those plants having AOB denitrification as the main N2O producing process. However, in treatment plants having incomplete NH2OH oxidation as the main N2O producing pathway, a cascade controller configuration adapting the oxygen supply to respect only the effluent ammonium concentration limits was found to be more effective to ensure low N2O emissions.

Impact pressure and void fraction due to plunging breaking wave impact on a 2D TLP structure

Violent impacts due to the plunging breaking wave impingement on a 2D tension-leg platform (TLP) structure were experimentally investigated in a laboratory. Simultaneous pressure, void fraction, fluid velocity, and structure motion measurements were performed on the multiphase, turbulent flow. The maximum mean impact pressure is 2.3ρC 2 with C being the wave phase speed. The pressure maximum and its rise time are negatively correlated, and the rise time for impulsive-type impacts is less than 15 ms or 0.18H/C with H being the wave height. Different approaches show that impact coefficients vary from 0.6 to 9.7, including relating the impact pressure maxima to the wave phase speed, local velocity, and void fraction. By modeling the plunging breaking wave impact as a filling flow, a pressure–aeration relationship was investigated and compared with the approximate solution derived by Peregrine and Thais (J Fluid Mech 325:377–397, 1996). The measured data show that a high aeration level tends to reduce the impact pressure maximum so the cushioning effect is significant for breaking wave impacts on a moving vertical wall.

Lipid content and fatty acid composition of Porosira glacialis and Attheya longicornis in response to carbon dioxide (CO2) aeration.

In the current study two novel psychrophilic diatoms Porosira glacialis and Attheya longicornis were tested for suitability to CO2 mitigation coupled with production of the physiologically requisite omega– 3 fatty acids. This study is in line with the worldwide conducted research aimed at applying biorefinery concept to heavy polluting industries. Since the production of algal high value compounds, i.e. essential fatty acids, relies on utilization of residual CO2 emissions coming from industry, the costs of such production maybe substantially reduced. Besides, the ecological benefits of the biorefinery concept being implemented are obvious, since CO2 is one of the major greenhouse gases. The current research has shown that one of the tested microalgal species, the diatom P. glacialis showed good tolerance to high (20–25%) levels of CO2 and maintained growth rates comparable to controls. The total lipid content in the CO2 aerated culture increased from 8.91 to 10.57% in cell dry mass. Additionally, the content of docosahexaenoic acid (DHA) increased from 3.90 to 5.75%, while the concentration of eicosapentaenoic acid (EPA) decreased from 26.59 to 23.66%. In contrast, A. longicornis did not demonstrate any significant increase in total lipid content. Besides, its growth was hampered by high levels of CO2 aeration.

Aerated biofilters with multiple-level air injection configurations to enhance biological treatment of methane emissions

Aiming to improve conventional methane biofilter performance, a multiple-level aeration biofilter design is proposed. Laboratory flow-through column experiments were conducted to evaluate three actively-aerated methane biofilter configurations. Columns were aerated at one, two, and three levels of the bed depth, with air introduced at flow rates calculated from methane oxidation reaction stoichiometry. Inlet methane loading rates were increased in five stages between 6 and 18mL/min. The effects of methane feeding rate, levels of aeration, and residence time on methane oxidation rates were determined. Samples collected after completion of flow-through experiments were used to determine methane oxidation kinetic parameters, Vmax, Km, and methanotrophic community distribution across biofilter columns. Results obtained from mixed variances analysis and response surfaces, as well as methanotrophic activity data, suggested that, biofilter column with two aeration levels has the most even performance over time, maintaining 85.1% average oxidation efficiency over 95days of experiments.

New Insights into the Anti-pathogenic Potential of Lactococcus garvieae against Staphylococcus aureus Based on RNA Sequencing Profiling.

The bio-preservation potential of Lactococcus garvieae lies in its capacity to inhibit the growth of staphylococci, especially Staphylococcus aureus, in dairy products and in vitro. In vitro, inhibition is modulated by the level of aeration, owing to hydrogen peroxide (H2O2) production by L. garvieae under aeration. The S. aureus response to this inhibition has already been studied. However, the molecular mechanisms of L. garvieae underlying the antagonism against S. aureus have never been explored. This study provides evidence of the presence of another extracellular inhibition effector in vitro. This effector was neither a protein, nor a lipid, nor a polysaccharide, nor related to an L-threonine deficiency. To better understand the H2O2-related inhibition mechanism at the transcriptome level and to identify other mechanisms potentially involved, we used RNA sequencing to determine the transcriptome response of L. garvieae to different aeration levels and to the presence or absence of S. aureus. The L. garvieae transcriptome differed radically between different aeration levels mainly in biological processes related to fundamental functions and nutritional adaptation. The transcriptomic response of L. garvieae to aeration level differed according to the presence or absence of S. aureus. The higher concentration of H2O2 with high aeration was not associated with a higher expression of L. garvieae H2O2-synthesis genes (pox, sodA, and spxA1) but rather with a repression of L. garvieae H2O2-degradation genes (trxB1, ahpC, ahpF, and gpx). We showed that L. garvieae displayed an original, previously undiscovered, H2O2 production regulation mechanism among bacteria. In addition to the key factor H2O2, the involvement of another extracellular effector in the antagonism against S. aureus was shown. Future studies should explore the relation between H2O2-metabolism, H2O2-producing LAB and the pathogen they inhibit. The nature of the other extracellular effector should also be determined.

Analysis of the efficiency of recombinant Escherichiacoli strain cultivation in a gas-vortex bioreactor.

The levels of aeration and mass transfer are critical parameters required for an efficient aerobic bioprocess, and directly depend on the design features of exploited bioreactors. A novel apparatus, using gas vortex for aeration and mass transfer processes, was constructed in the Center of Vortex Technologies (Novosibirsk, Russia). In this paper, we compared the efficiency of recombinant Escherichia coli strain cultivation using novel gas-vortex technology with conventional bioprocess technologies such as shake flasks and bioreactors with mechanical stirrers. We demonstrated that the system of aeration and agitation used in gas-vortex bioreactors provides 3.6 times higher volumetric oxygen transfer coefficient in comparison with mechanical bioreactor. The use of gas-vortex bioreactor for recombinant E.coli strain cultivation allows to increase the efficiency of target protein expression at 2.2 times for BL21(DE3)/pFK2 strain and at 3.5 times for auxotrophic C600/pRT strain (in comparison with stirred bioreactor).

Perbanyakan In Vitro Dendrobium Indonesia Raya ‘Ina’ melalui Embriogenesis Somatik Berbasis Sistem Bioreaktor

<pre><em></em><em>ABSTRACT<br /><br />An effective and efficient in vitro propagation system has important roles in preparing and producing high quality-seedlings of Dendrobium for commercial scale. The objective of this research was to establish an effective and efficient embryogenic callus (EC) proliferation method using bioreactor system and regeneration EC into plantlet for producing high quality seedlings of Dendrobium Indonesia Raya ‘Ina’. Differences in callus densities (5, 10, 15, and 20 g callus in 250 mL medium), aeration levels (2.5, 5.0, and 10.0 O2 volume per medium volume per minute; vvm), and regeneration media half-strength MS and 2 g L-1 NPK (32:10:10) combinated by 0.00, 0.05 mg L-1 BA, 150 mL L-1 coconut water and their combinations were tested in this experiment. The experiments were arranged using randomized completely block design (RCBD) with three replications for EC proliferation and randomized completely desaign (RBD) for EC regeneration. The results showed that combination of aeration at 2.5 vvm and 10 g of EC was the most suitable aeration level and callus density for proliferation of EC in the 500 ml airlift bioreactor with 6.85 multiplication rate, 92.5% EC formation, and malformed callus morphology as low as 6.1%. The highest somatic embryos (SEs) formation was 87.7% with 44.5 SEs per clump and 92.1% SEs germination with 41.0 germinated-SEs per clump, 85.1% normal germinated-SEs, and whereas the best performance of plantlet was obtained from 1/2 MS + 0.05 mg L-1 BA semi solid medium. Plantlets were successfully acclimatized using Cycas rumphii medium with high survival rate (91.6%). <br /><br />Keywords: aerations, callus densities, germination, media, somatic embryos<br /><br /></em></pre>

Respiration Rates of Organic Soil Depending on Changes of Moisture and Aeration

This paper aims at analyzing changes in soil respiration depending on the levels of soil moisture and aeration. Organic forest soil was used in the experiments. Watering of the soil was applied starting from two initial moisture contents: 1) GWC > 0.1, desiccated soil, respiration equals to zero; 2) GWC between 0.46 - 0.78, moisture of the soil approximately the same as at the time of sample collection. Watering of the soil was applied once or continuously during the experiment. The experiments were conducted under both: unrestricted air-supply and anoxic conditions. Measurements of: oxygen consumption, carbon dioxide emission, and RQ were determined with a volumetric respirometer. Soil desiccation, which occurs under good access of the air, and leads to the increase of respiration rate (the “Birch effect”), is predominantly related to aerobic respiration following the change in soil aeration. If respiration of non-desiccated soil is assumed as 100%, the oxygen consumption of desiccated soil equaled to 209.90% of such value in the non-desiccated soil at the lowest moisture level, and only to 51% at the highest. Carbon dioxide emission equaled to 191.92% and 111% at the lowest and the highest moisture levels, respectively. Desiccation did not increase the respiration rate under anoxic conditions. It either decreased or remained statistically unchanged. However, obtained values of RQ index suggest that under anoxic conditions desiccation affects fermentation processes in the soil. The value of RQ index at the moisture level lower than GWC 1 was very low attaining merely 0.3 - 0.4, which suggests active fermentation processes. At higher moisture content yet, RQ value exceeded 2.

Yields and Nutritional of Greenhouse Tomato in Response to Different Soil Aeration Volume at two depths of Subsurface drip irrigation

This study investigated the effects of 4 aeration levels (varied by injection of air to the soil through subsurface irrigation lines) at two subsurface irrigation line depths (15 and 40 cm) on plant growth, yield and nutritional quality of greenhouse tomato. In all experiments, fruit number, width and length, yield, vitamin C, lycopene and sugar/acid ratio of tomato markedly increased in response to the aeration treatments. Vitamin C, lycopene, and sugar/acid ratio increased by 41%, 2%, and 43%, respectively, in the 1.5 times standard aeration volume compared with the no-aeration treatment. An interaction between aeration level and depth of irrigation line was also observed with yield, fruit number, fruit length, vitamin C and sugar/acid ratio of greenhouse tomato increasing at each aeration level when irrigation lines were placed at 40 cm depth. However, when the irrigation lines were 15 cm deep, the trend of total fruit yields, fruit width, fruit length and sugar/acid ratio first increased and then decreased with increasing aeration level. Total soluble solids and titrable acid decreased with increasing aeration level both at 15 and 40 cm irrigation line placement. When all of the quality factors, yields and economic benefit are considered together, the combination of 40 cm line depth and “standard” aeration level was the optimum combination.

Use of Computational Combustion in the Development and Design of Energy-Efficient Household Cooker-Top Burners

In order to design energy efficient cooker-top burners, the stabilization mechanisms of partially premixed flames were investigated. Different design features are assessed with the identical fuel (CH4), fuel flow rate, and load vessel arrangement, but with different levels of primary aeration and flame delivery. k–ε Reynolds-averaged Navier–Stokes (RANS) simulations are performed using the modified temperature-composition pdf method and the intrinsic low-dimensional manifold (ILDM) reduction scheme. The results show that the optimum value of the angle of flame delivery is about 30–35 deg. The contact area of the flame cup under the bottom surface depends on the diameter of the burner head which determines the separation of the flames. The traditional solution to reduce the port separations, which is to increase the number of ports, is shown to cause weak flames which extinguish in shorter distances and can have strong tendency to blow off. It also causes significant pressure resistance ahead of the contraction tube and so impairs the primary aeration. In the present study, a new slot profile, named the double-V form, is proposed and shown to be very effective in reducing the gaps between the flames, without creating any further pressure resistance.

Economics of Intensively Aerated Catfish Ponds

AbstractTheUScatfish industry is evolving by adopting production‐intensifying practices that enhance productivity. Catfish producers have increased aeration rates over time, and some now use intensive rates of aeration (>9.33kW/ha). Costs and production performance were monitored at commercial catfish farms using high levels of aeration (11.2–18.7 kW/ha) in Alabama, Arkansas, and Mississippi. A multivariate‐cluster analysis was used to identify four different management clusters of intensively aerated commercial catfish farms based on stocking density, size of fingerlings at stocking, and feed conversion ratios (FCR). Breakeven prices of hybrid catfish raised in intensively aerated pond systems were estimated to range from $1.86/kg to $2.17/kg, with the lowest costs associated with the second greatest level of production intensity. The two medium‐intensity clusters generated sufficiently high revenues for long‐term profitability. However, the least‐intensive and the most‐intensive clusters were economically feasible only when catfish and feed prices were closer to less probable market prices. Feed price,FCR, and yield contributed the most to downside risk. Intensive aeration in catfish ponds, up to the levels analyzed in this study, appears to be economically feasible under the medium‐intensity management strategies identified in this analysis.

Systematic engineering of TCA cycle for optimal production of a four-carbon platform chemical 4-hydroxybutyric acid in Escherichia coli

To address climate change and environmental problems, it is becoming increasingly important to establish biorefineries for the production of chemicals from renewable non-food biomass. Here we report the development of Escherichia coli strains capable of overproducing a four-carbon platform chemical 4-hybroxybutyric acid (4-HB). Because 4-HB production is significantly affected by aeration level, genome-scale metabolic model-based engineering strategies were designed under aerobic and microaerobic conditions with emphasis on oxidative/reductive TCA branches and glyoxylate shunt. Several different metabolic engineering strategies were employed to develop strains suitable for fermentation both under aerobic and microaerobic conditions. It was found that microaerobic condition was more efficient than aerobic condition in achieving higher titer and productivity of 4-HB. The final engineered strain produced 103.4g/L of 4-HB by microaerobic fed-batch fermentation using glycerol. The aeration-dependent optimization strategy of TCA cycle will be useful for developing microbial strains producing other reduced derivative chemicals of TCA cycle intermediates.

Optimization of growth of two microalgal isolates for biofuel feedstock

A research involving random isolation and characterization of naturally occurring microalgae in Bangladesh was carried out for assessing their potential for biofuel feedstock and other uses. Among the isolates, one identified as a green alga Chlamydomonas noctigama and another one as blue-green alga Nostoc spongiaeforme were grown in modified Chu-10D medium. The optimization of their growth was performed following incubation of the isolates under different levels of media concentration, temperature, pH, light intensity and aeration. Both the species showed optimum growth in terms of total chlorophyll at a temperature of 25oC. However, significant differences (at 5% level) in growth were observed for the isolates under other conditions. The optimum growth of Chlamydomonas noctigama was observed for the vitamin B1+B6, whereas there was no significant difference on growth of Nostoc spongiaeforme for any vitamin supplement. The optimum pH for the growth of Chlamydomonas noctigama and Nostoc spongiaeforme were 6.5 and 7.5, light intensity 110 µEm-2s-1and 70 µEm-2s-1, and media concentration 2x and 1x of normal concentration, respectively.Bangladesh J. Sci. Ind. Res.51(3), 183-192, 2016

Effects of Artificial Soil Aeration Volume and Frequency on Soil Enzyme Activity and Microbial Abundance when Cultivating Greenhouse Tomato

Core Ideas Rhizosphere soil enzymes activity showed an initial increase followed by a decrease. Soil aeration can enhance the activities of three rhizosphere soil enzymes. Aeration frequency and volume can significantly affect rhizosphere enzyme activities. Aeration can enhance the activities of non‐rhizosphere soil enzymes. Soil aeration can increase tomato yield. Artificial soil aeration can enhance soil enzyme activity, improve soil nutrient cycling, and increase crop growth and yield. We studied the response of soil microorganisms and soil enzyme activity to two levels of burial depths of subsurface tubing in combination with four levels of aeration volume and three frequency levels of supplemental soil aeration. The aeration volumes (V) were 0, 0.5, 1, and 1.5 times (CK, V1, V2, and V3, respectively) the estimated porosity of the plot rhizosphere. Burial depths (D) of subsurface tubing were 15 and 40 cm (D15 and D40). Aeration frequencies (F) levels were none and at 2‐ and 4‐d intervals (CK, F2, and F4). The results demonstrated that aeration frequency and volume positively affected soil urease, phosphatase, and catalase activity and soil microbial abundance. The impact of aeration treatment on rhizosphere soil enzyme activity was greater than its impact on non‐rhizosphere activity. When the drip irrigation tube depth was 15 cm, V2 volume with 2‐d aeration intervals led to an increase in the mean yield of first picking fruit of 75.1% compared with the unaerated control. When V3 volume with 2‐d aeration intervals was performed with a 40‐cm irrigation tube, the mean yields of the first picking fruit increased by 135.5% compared with the unaerated control. These results suggest that artificial soil aeration can improve the plant root zone environment, increase microbial abundance and soil enzyme activity, and promote nutrient uptake, thus promoting plant growth and fruit output.

Performance evaluation of micro-aerobic hydrolysis of mixed sludge: Optimum aeration and effect on its biochemical methane potential

ABSTRACTThis study evaluated the performance of a micro-aerobic hydrolysis of mixed sludge and its influence as a pretreatment of this waste for its subsequent anaerobic digestion. Three experimental series were carried out to evaluate the optimum micro-aeration levels in the range from 0.1 to 0.5 air volume/min.reactor volume (vvm) and operation times within the range of 24–60 h. The maximum methane yield [35 mL CH4/g volatile suspended solids (VSS) added] was obtained for an aeration level of 0.35 vvm. This methane yield value increased 114% with respect to that obtained with the non-aerated sludge. In the micro-aeration process carried out at an aeration level of 0.35 vvm, increases in soluble proteins and total sugars concentrations of 185% and 192% with respect to their initial values were found, respectively, after 48 h of aeration. At the above micro-aerobic conditions, soluble chemical oxygen demand (CODS) augmented 150%, whereas VSS content decreased until 40% of their initial respective values. Higher COD increases and VSS decreases were found at 60 h of micro-aeration, but the above parameters did not vary significantly with respect to the values found at 48 h.

Exploitation of Agricultural Wastes and By-Products for Production of Aureobasidium pullulans Y-2311-1 Xylanase: Screening, Bioprocess Optimization and Scale Up

The potential of several agricultural wastes and by-products (wheat bran, oat bran, corn cob, brewer’s spent grain, malt sprout, artichoke stem, sugar beet pulp, olive seed, cotton stalk and hazelnut skin) was examined as the substrate for xylanase production by Aureobasidium pullulans Y-2311-1. Based on the screening studies, wheat bran was selected as the best substrate for further optimization studies. The effects of initial medium pH, temperature and incubation time on xylanase production in shake flask system were optimized by response surface methodology (RSM). The optimum levels of the process variables defined by the model (initial medium pH, 4.24; temperature, 30.27 °C; and incubation time 126.67 h) resulted in production of 85.19 U/ml xylanase. Taking the RSM optimized parameters in shake-flask scale into consideration; xylanase production was scaled up to bioreactor system with a working volume of 1.5 l. The peak of enzyme production was achieved after 126 h incubation that has previously been determined by RSM studies at shake flask level. Furthermore, the optimum levels of agitation and aeration in bioreactor system was found as 200 rpm and 1.5 vvm. Maximum enzyme production was close to 85 kU/l which could be translated into a productivity of 0.68 kU/l/h. No previous work considered the statistical optimization of xylanase production by A. pullulans on wheat bran and scale up of the bioprocess to a bioreactor system.

Sludge reduction using aquatic worms under different aeration regimes

ABSTRACTAdding aquatic worms to a wastewater treatment system can reduce sludge production through predation. The aeration level is crucial for success. To evaluate aeration impacts on sludge reduction and determine an optimal aeration regime, this study investigated the processes of in-situ sludge reduction, using aquatic worms exposed to different aeration levels. The experiment also compared treatment results between a conventional reactor and an aquatic worm reactor (WR). Results indicated that the recommended concentration of dissolved oxygen (DO) was 2.5 mg L−1. The removal rate of chemical oxygen demand remained steady at 80% when the DO concentration was higher than 2.5 mg L−1, while the removal rate of ammonia nitrogen continued to moderately increase. Increasing the DO concentration to 5 mg L−1 did not improve sludge reduction, and consumed more power. With a DO concentration of 2.5 mg L−1 and a power of 0.19 kWh t−1 water, the absolute sludge reduction and relative sludge reduction rates in the WR were 60.0% and 45.7%, respectively, and the daily aquatic worm growth rate was 0.150 d−1 during the 17-d test. Therefore, at the recommended aeration regime, aquatic worms reduced the sludge without increasing the power consumption or deteriorating the effluent.

Self-similarity and scale effects in physical modelling of hydraulic jump roller dynamics, air entrainment and turbulent scales

A physical study of hydraulic jump is often undertaken using down-scaled Froude-similar models with Reynolds numbers much smaller than in prototype (e.g. spillway stilling basins). The potential viscous scale effects may affect a number of physical processes including turbulence development and air entrainment, thus challenging the extrapolation of laboratory data to the prediction of prototype conditions or justification of numerical modelling. This paper presents an experimental study of hydraulic jumps with a particular focus on the scale effects in terms of free-surface fluctuation and deformation, bubble advection and diffusion, bubble-turbulence interaction and turbulence dissipation. A broad range of free-surface, air–water flow and turbulence properties were measured systematically for Froude numbers from 3.8 to 10 and Reynolds numbers from 2.1 × 104 to 1.6 × 105. Based upon self-similarities in the longitudinal evolution of a number of characteristic flow properties, the analytical expressions of time-averaged roller surface profile, void fraction distribution and longitudinal velocity distribution were derived for given Froude number. The roller surface dynamics were found free of scale effects in terms of fluctuation amplitudes but the characteristic frequencies were scale-sensitive. While some air–water flow parameters such as bubble count rate, bubble chord time distribution and bubble grouping behaviour could only be correctly quantified at full-scale prototype conditions, the aeration level and turbulent scales might be estimated with satisfactory accuracy for engineering applications given a model Reynolds number no less than 4 × 10 to 6 × 104.