Abstract Numerical models are widely used to simulate volcanic gas dispersion and estimate local emission sources. However, significant uncertainties arise from the approximations inherent in their physical formulations. Recent advances in high-performance computing (HPC) have enabled high-resolution simulations with minimal numerical diffusion, revealing previously unnoticed limitations in the Monin–Obukhov Similarity Theory used within atmospheric gas dispersion models. One key issue is the determination of the minimum vertical turbulence diffusion coefficient (Kz min ) in the atmospheric surface layer (ASL), which plays a crucial role in reducing biases in advection–diffusion models caused by inadequate turbulence representation. In this study, we refine the Eulerian passive gas transport model DISGAS (v. 2.5.1) using measured data on fumarolic and diffuse CO₂ fluxes and air concentrations, along with local wind measurements collected during an ad hoc field campaign from 4 to 10 May 2023. To account for uncertainties in gas flow rates and turbulent velocity fluctuations, we conducted a statistically robust set of simulations by varying CO₂ fluxes and Kz min values. Model outputs were compared with in situ CO₂ concentration measurements at fixed monitoring stations. Results indicate that during stable atmospheric conditions, setting Kz min within the range of 1.5–2 m 2 s −1 significantly improves agreement with observations and reduces systematic biases in source estimation. These findings refine model parameterization to better represent turbulence under stable atmospheric conditions at La Solfatara crater during the May 2023 survey. Moreover, the proposed methodology can be adopted for automated data assimilation workflows aimed at constraining unknown fumarolic gas source fluxes in other volcanic settings. Graphical Abstract

Abstract Numerical models are widely used to simulate volcanic gas dispersion and estimate local emission sources. However, significant uncertainties arise from the approximations inherent in their physical formulations. Recent advances in high-performance computing (HPC) have enabled high-resolution simulations with minimal numerical diffusion, revealing previously unnoticed limitations in the Monin-Obukhov Similarity Theory used within atmospheric gas dispersion models. One key issue is the determination of the minimum vertical turbulence diffusion coefficient (Kzmin) in the Atmospheric Surface Layer (ASL), which plays a crucial role in reducing biases in advection-diffusion models caused by inadequate turbulence representation. In this study, we refine the Eulerian passive gas transport model DISGAS (v. 2.5.1) using measured data on fumarolic and diffuse CO₂ fluxes and air concentrations, along with local wind measurements collected during an ad hoc field campaign from 4–10 May 2023. To account for uncertainties in gas flow rates and turbulent velocity fluctuations, we conducted a statistically robust set of simulations by varying CO₂ fluxes and Kzmin values. Model outputs were compared with in situ CO₂ concentration measurements at fixed monitoring stations. Results indicate that during stable atmospheric conditions, setting Kzmin within the range of 1.5–2 m² s− 1 significantly improves agreement with observations and reduces systematic biases in source estimation. These findings refine model parameterization to better represent turbulence under stable atmospheric conditions at La Solfatara crater during the May 2023 survey. Moreover, the proposed methodology can be adopted for automated data assimilation workflows aimed at constraining unknown fumarolic gas source fluxes in other volcanic settings.

Abstract Inlet Gas Void Fraction (IGVF) and rotating speed are key parameters influencing the flow characteristics of gas-liquid multiphase pumps. To explore the influence of these two factors on the flow characteristics of gas-liquid multiphase rotodynamic pumps, CFD simulations were carried out based on the Euler two-fluid model to analyze the flow characteristics in an axial-flow pump at three different rotating speeds (1450 r/min, 2200 r/min, 2950 r/min) with different IGVFs. The numerical results indicate that the pump efficiency and head are first increased and then decreased with the increase of IGVF. When the IGVF is 5%, the head and efficiency reach their maximum values. This is attributed to the minimum vorticity and turbulence kinetic energy in the impeller passage at IGVF= 5%, and the small vortex range at the hub of the guide vane, thus resulting in the stable two-phase flow state in the impeller and guide vane. At the same IGVF, with the increase of the rotating speed, the head and efficiency of the multiphase pump increase accordingly. This is closely related to the smallest vortex range formed by gas-liquid flow separation at n=2950 r/min, indicating a better flow state.

In this study, we analytically derived the Rytov variance and scintillation index value of turbulence caused by jet engines. In addition, we analyzed the variation characteristics of the Rytov variance and scintillation index values numerically depending on the variations in turbulence strength, experimental data, and wavelength. We observe that Rytov variance reaches up to high values due to the strong turbulence resulting from high refractive index fluctuations. This result brings high-intensity fluctuations regardless of the anisotropy of the turbulence. Rytov variance is directly proportional to turbulence strength. We present scintillation index curves considering the aperture averaged case. We plot our results considering the variations in the operating wavelength, turbulence strength, and the scaling parameter. According to our results, we think that it will be useful for a system such as directed infrared countermeasure (DIRCM), which is highly sensitive and should be exposed to minimum turbulence in the field of use. Since DIRCMs transmit codes to paralyze the missile’s seeker, intensity fluctuations play a vital role during this transmission. It could reduce the performance of these systems when intensity fluctuations are high.

Effects of tip clearance on energy performance of three-stage electrical submersible pump

A numerical study of the effect of building height and shape on amount of wind energy available on the roof

In this study, we analyze portfolio performance under different methods and scenarios for the small island economy of Fiji. In addition to documenting the historical performance and the smallness of the stock market, the study looks at the possibility of opting for an equally weighted (naïve) portfolio against market and minimum variance portfolios. To this end, we extract monthly stock price data of 17/19 listed companies from August 2019 to July 2022 and invoke different approaches to develop portfolios under different scenarios. We consider the mean-variance, minimum variance, semi-variance, utility maximization, and minimum turbulence portfolios, based on beta-adjusted (CAPM-based) returns. The different portfolios presented in the study should provide some insights on asset allocation in Fiji’s stock market. Interestingly, unlike average returns, the beta-adjusted returns indicate that an equally weighted portfolio can yield relatively higher expected returns than market portfolios, although, with a relatively higher standard deviation and lower Sharpe ratio than the optimized results. In a semi-variance analysis (where we account for downside risk only), equally weighted portfolio yields superior returns, albeit with a relatively lower Sortino ratio. Given that Fiji’s stock market is currently a small, with a relatively small number of listed companies, potential and less sophisticated investors and analysts considering portfolios based on beta-adjusted returns, may simply opt for 1/N (naïve) portfolios as a diversification strategy while realizing decent expected returns. The optimized portfolio under mean-variance, semi-variance, and utility are presented as alternative considerations for nuanced investors. Additionally, equally weighted turbulence-adjusted and minimum-turbulence portfolios are constructed to capture periods of unusualness and calmness in the market. The methodologies and the results presented can be adjusted and applied to other small markets and hence can influence investment decisions of investors in creating diversified portfolios under different scenarios.

The effect of the hydrodynamic situation (mainly conditions of mixing of the solutions of the reagents) on the composition and sizes of the nanoparticles being formed in an impinging-jet microreactor (IJMR) upon the impinging of the jets of the reagents—aqueous solutions of lanthanum nitrate and ammonium dihydrogen phosphate—is studied. Unique conditions are generated in the IJMR providing a short-term contact of the jets of the solutions that move at a high velocity (of about 10–20 m/s). The characteristics of turbulence in the IJMR are calculated. It is shown that the rate of dissipation of turbulent kinetic energy in the zone of impinging of the jets may reach 107–109 W/kg, which is comparable to the level of dissipation of energy in ultrasonic baths and is several orders of magnitude higher when compared to almost any other type of reactor. The effect of the region that has a size of the minimum Kolmogorov turbulence scale, i.e., a self-organizing “nanoreactor,” on the size of the particles being formed upon the deposition of particles with a complex composition is determined. Comparing the results of the calculation with the experimental data shows that, in some cases, the volume of the nanoreactor, taking into account the concentration of the solutions, determines the weight and size of the particles being formed. An explanation for the effect of a different influence of the velocity of impingement of the jets on the size of the nanoparticles being formed during the microreactor mixing of the reagents, depending on the characteristic features of the mechanisms of chemical reactions under the conditions of “soft” chemistry, is provided.

This paper presents the design and manufacturing of open circuit low-speed wind tunnel. The design of the contraction cone, test section and diffuser are finalized by the numerical analysis performed on ANSYS CFD software. A unique insight into the design of the contraction cone is presented. A fifth-order polynomial is used to model the contraction cone in PRO-E software. It allowed designing the test section with minimum turbulence and flow serration and a flow velocity profile of 20 m/s. The cross-sectional area of the test section and diffuser are selected after analytical calculations. The diffuser is designed as such to avoid pressure loss by incorporation changes in the rectangular cross-section. The initial study performed on the design helped us to select the fan with suitable power. Moreover, the intake of the contraction cone is equipped with the honeycomb structure of facilitating the laminar flow into the contraction cone. Following on to the initial numerical analysis, the fabrication of the wind tunnel is performed. Besides, a separate lift/drag measuring force system is also prepared; the intuitive design is cost-effective as well as accurate. The placement of anemometer helped us to directly measure the test section velocity, which is found to be 17 m/s.

Heat transfer characteristics of impinging jet on a hot surface with constant heat flux using Cu2O–water nanofluid: An experimental study

A channel centrifugal pump has been developed which have calculated parameters during the nominal operating mode based on 3-dimensional computer simulation (flow rate 5 l/min, pressure drop 100 mm). In addition, pump’s operating conditions in ECMO mode are considered at high pressure drops of 200–300 mm Hg with a speed of rotor up to 3500 rpm. Simulation result was a creation of a new channel- type centrifugal pump with shear stress that do not exceed the allowable threshold of 150 Pa, and also minimizing stagnation and flow recirculation zones. The obtained data were also the result of use design of rotor with constant cross-section channels formed along a logarithmic curve and ensuring minimum turbulence due to the minimum outlet angle of the flow.

Mixed-lubrication analysis of misaligned bearing considering turbulence

The goal of wind tunnel design is to generate a uniform air flow with minimum turbulence intensity and low flow angle. The nozzle is the main component of wind tunnels to create a uniform flow with minimal turbulence. Pressure distribution along nozzle walls directly affects the boundary layer thickness, pressure losses and non-uniformity of flow velocity through the test section. Although reduction of flow turbulences and non-uniformity through the test section can be carried out by nozzles with high contraction ratio, it increases the construction cost of the wind tunnel. For decreasing the construction cost of nozzle with constant test section size and mass flow rate, the contraction ratio and length of nozzle should be decreased; that causes the non-uniformity of outlet velocity to increase. In this study, first, three types of nozzle are numerically investigated to compare their performance. Then, Sargison nozzle with contraction ratio of 12.25 and length of 7 m is scaled down to decrease its weight and construction cost. Having scaled and changed to a nozzle with contraction ratio of 9 and length of 5 m, its numerical solution reveals that the non-uniformity of outlet velocity increases by 21%. By using the Ballspine inverse design method, the pressure distribution of the original Sargison nozzle is first scaled and set as the target pressure of the scaled down nozzle and geometry correction is done. Having reached the target nozzle, numerical solution of flow inside the optimized nozzle shows that the non-uniformity just increases by 5% in comparison with the original Sargison nozzle.

ABSTRACTIn spite of much progress in the development of gasoline direct injection (GDI) engines, choosing an appropriate piston top contour to obtain desirable combustion efficiency is still an arduous process for engineers. This study investigates the combined effects of piston bowl geometry and a charge motion control valve (CMCV) on tumble flow and combustion features in GDI engines. Based on the model validation, the processes of intake, spray, mixture formation and combustion at different engine speeds are simulated and analyzed for different piston shapes for the two cases of opening and closing the CMCV. The results show that the bowl on the top of piston is beneficial for the formation and development of tumble flow. The flat top piston with the CMCV closed is able to achieve acceptable combustion pressure. However, with the increase of engine speed and load, the advantages of the flat top pistons gradually disappear; the dual offset bowl piston has a minimum tumble ratio and turbulence kinetic energy (TKE) at the end of the compression stroke because of the projection in the middle of the piston top surface which leads to a lower pressure rise rate and a reduced flame propagation speed at high load. The closed CMCV contributes to a faster evaporation rate and a more uniform mixture at lower speeds. It is not recommended for use at high speeds due to lower intake air mass and reduced combustion pressure. The research provides an effective way for engineers to choose an appropriate piston top contour combined with a CMCV to obtain desirable combustion efficiency.

The U.S. Environmental Protection Agency (EPA) short-distance dispersion model, AERMOD, has been shown to overpredict by a factor of as much as 10 when compared with observed concentrations from continuous releases at the Oak Ridge, TN (OR), and Idaho Falls, ID (IF), field experiments during stable periods when wind speeds often dropped below 1 m/sec. Some of this overprediction tendency can be reduced by revising AERMOD's meteorological preprocessor's parameterizations of the friction velocity, u * , during low-wind stable conditions, thus increasing the calculated σ v and σ w and hence the lateral and vertical dispersion rates. Observations show that as the mean wind speed approaches zero at night, there is always significant σ v and σ w over time periods of 15 to 60 min, while standard Monin–Obukhov Similarity Theory (MOST) predicts that σ v and σ w will approach zero. This paper focuses on the u * estimation methods and the minimum turbulence (σ v and σ w ) assumptions in AERMOD (beta option 4) and two widely used U.S. operational dispersion models, AERMOD (v12345) and SCICHEM. The U.S. EPA has provided results of its tests with the OR and IF data, with its base AERMOD version and its December 2012 modified versions, which assume adjustments to the low-wind u * and increases in the minimum σ v parameterization. SCICHEM has relatively small mean bias for both data sets. The revised AERMOD shows much less mean bias, agreeing more with SCICHEM. Implications: Suggestions are made for improvements to dispersion models such as AERMOD to correct overpredictions during light-wind stable conditions. Methods for estimating u*, L, and the minimum turbulence parameters (σv and σw) are reviewed and compared. SCICHEM and the current operational version and an optional beta version (December 2012) of AERMOD are evaluated with tracer data from low-wind stable field experiments in Idaho Falls and Oak Ridge. It is seen that the operational version of AERMOD overpredicts by a factor of 2 to 10, while the optional beta version of AERMOD and SCICHEM have much less bias.

Novel design and experimental validation of a contraction nozzle for aerodynamic measurements in a subsonic wind tunnel

The use of diffuser in wind turbine (DAWT) is aimed at increasing the effective speed to produce a higher power. A bigger and heavier turbine results in difficulty in manufacturing the turbine orientation system. This research consists of three parts i.e. the calculation and analysis of the losses, determination of the effective diameter of the rotor, and the calculation and analysis of the absorbed energy by DAWT. The losses calculation and analysis is based on the friction between the airflow and wall. The diameter of the rotor is choosen in the diffuser area which has minimum turbulence flow produced by the wind angle. The calculation and analysis of the power is based on its rotor diameter. Then the power converted to become energy. In this research, DAWT is assumed to have no orientation system so that easily manufactured, i.e. the rotor is oriented at a single direction. Wind direction and frequency is selected in three configurations. In the first configuration, the wind direction comes from all the twelve wind source direction with the same frequency in the 24 hour period, producing 2 hourly periods for every wind direction. In the second configuration, wind from 90° and 270° or perpendicular to the axial turbine axes are eliminated, and hence producing 10 different wind directions at 2.4 hourly periods. In the third configuration, the turbine is set at the beach whereby the wind direction comes only at two direction; the sea and land wind directions. At these conditions, the wind is assumed to come at 0°, 30°, 150°, 180°, 210°, and 330°. The aim of this research is to calculate the energy absorption of the wind rotor, and comparing with those produced without the diffuser system in place. In this research, a 2m rotor diameter and 4m diffuser diameter is selected, power coefficient of 0.3, wind speed of 5m/sec, and these parameters are constant for the 24 period under analysis. The result of the calculation shows that there are losses near wall especially for high wind angle. The rotor diameter have chossen about 1,940 m. The energy absorption of the wind rotor without the diffuser is 6.231 kJ. The energy absorption values for the 1st, 2nd and 3rd configuration with the diffuser produce 54.361, 65.234, and 101.316 kJ respectively. It shows that the use of diffuser in the wind rotor could produce an increase of up to 9 to 16 times in the power absorption of the rotor. Keywords: Wind turbine, DAWT, Electrical energy, Losses

A theory of the effect of the geodesic acoustic mode (GAM) on turbulence is presented. Two synergistic issues are elucidated: namely, the physics of the zonal flow modulation and its role in the L-H transition, and the role of the GAM wave group propagation in turbulence spreading. Using a wavekinetic modulational analysis, the response of the turbulence intensity field to the GAM is calculated. This analysis differs from previous studies of zero-frequency zonal flows since it accounts for resonance between the drift wave group speed and the GAM strain field, which induces secularity. This mechanism is referred to as secular stochastic shearing. Finite real frequency and radial group velocity are intrinsic to the GAM, so its propagation can induce nonlocal phenomena at the edge and pedestal regions. To understand the effect of the GAM on turbulence and transition dynamics, a predator-prey model incorporating the dynamics of both turbulence and the GAMs is constructed and analyzed for stability around fixed points. Three possible states are identified, namely, an L-modelike stationary state, a reduced turbulence state, and a GAM limit-cycle state. The system is attracted to the state with the minimum turbulence level.

The relationship of turbulence quantities to mean flow quantities, such as the Richardson number, degenerates substantially for strong stability, at least in those studies that do not place restrictions on minimum turbulence or non-stationarity. This study examines the large variability of the turbulence for very stable conditions by analyzing four months of turbulence data from a site with short grass. Brief comparisons are made with three additional sites, one over short grass on flat terrain and two with tall vegetation in complex terrain. For very stable conditions, any dependence of the turbulence quantities on the mean wind speed or bulk Richardson number becomes masked by large scatter, as found in some previous studies. The large variability of the turbulence quantities is due to random variations and other physical influences not represented by the bulk Richardson number. There is no critical Richardson number above which the turbulence vanishes. For very stable conditions, the record-averaged vertical velocity variance and the drag coefficient increase with the strength of the submeso motions (wave motions, solitary waves, horizontal modes and numerous more complex signatures). The submeso motions are on time scales of minutes and not normally considered part of the mean flow. The generation of turbulence by such unpredictable motions appears to preclude universal similarity theory for predicting the surface stress for very stable conditions. Large variation of the stress direction with respect to the wind direction for the very stable regime is also examined. Needed additional work is noted.

The article investigates the determinants of newly created industrial establishments in Brazil in 1997 taking as reference explanatory variables referring to market structure and industry dynamics, stronger effects are detected for larger firms. Minimum efficient scale, industry size, industry growth and turbulence display the expected positive effects on firm size, but the intensity of those are more pronounced for larger firms. The suboptimal scale variable, on the other hand, exhibits a counterintuitive positive effect and perhaps other types of barriers to entry that are not related to scale aspects may be important in the Brazilian case.