Orifice Flow Research Articles

The physical and numerical modeling to design the breast wall spillway – AS case study

ABSTRACT The river systems in the Himalayan region exhibit year-round flow due to precipitation during the rainy season and snow/glacier melt in summer. These rivers carry massive sediment loads, especially during monsoons. Hydraulic engineers face the challenge of designing infrastructure capable of managing this sediment. Breast wall spillways are recommended for their ability to handle floodwaters and sediment disposal. The hydraulics of breast wall/orifice spillways changes with the varying reservoir level. The flow is free flow for reservoir water levels below the top of the sluice, whereas for higher water levels the flow is orifice flow. Orifice spillways are designed to pass water through openings or gates, where the flow is primarily governed by the hydraulic head and the orifice size. The flatter bottom profile helps in smoothly directing the flow through the opening without causing significant turbulence or separation, especially when the gate is partially open. Hence, the crest profile is flatter as compared to the overflow crest profile to avoid flow separation and negative pressures on the crest for small gate openings. Kwar Hydro Electric Project is one such Himalayan region project planned across the Chenab River in which a breast wall spillway has been provided to serve the dual-purpose of flood and sediment disposal. The present paper describes the physical and numerical hydraulic model studies conducted for Kwar H .E. Project, Jammu and Kashmir, to evolve a breast wall spillway profile, ski jump type energy dissipator at the toe of the spillway.

Influence of compliance and resistance of the test lung on the accuracy of the tidal volume delivered by the ventilator

BackgroundLarge variations in respiratory system compliance and resistance may cause the accuracy of tidal volume (VT) delivery beyond the declared range. This study aimed at evaluating the accuracy of VT delivery using a test lung model to simulate pulmonary mechanics under normal or disease conditions.MethodsIn vitro assessment of the VT delivery accuracy was carried out on two commercial ventilators. Measurements of the inspired and expired VT from the ventilator and FlowAnalyser were compared to evaluate the separated and combined influences of compliance and resistance on the delivered VT accuracy. To do this, the errors of five delivered volumes (30 ml, 50 ml, 100 ml, 300 ml, and 500 ml) were checked under 29 test conditions involving a total of 27 combinations of resistance and compliance.ResultsFor the tested ventilator S1 with a flow sensor near the expiratory valve, the average of expired VT errors (ΔVTexp) in three measurements (4 test conditions for each measurement) correlated to test lung compliance (r=-0.96, p = 0.044), and the average of inspired VT errors (ΔVTins) correlated to compliance (r = 0.89, p = 0.106); for the tested ventilator S2 with a flow sensor located at the Y piece, no clear relationship between compliance and ΔVTexp or ΔVTins was found. Furthermore, on two ventilators tested, the current measurements revealed a poor correlation between test lung resistance and ΔVTins or ΔVTexp, and the maximum values of ΔVTexp and ΔVTins correspond to the maximum resistance of 200 cmH2O/(L/s), at which the phenomenon of the flap fluttering in the variable orifice flow senor was observed, and the recorded peak inspiratory pressure (Ppeak) was much higher than the Ppeak estimated by the classical equation of motion. In contrast, at the lower resistance values of 5, 20, 50 and 100 cmH2O/(L/s), the recorded Ppeak was very close to the estimated Ppeak. Overall, the delivered VT errors were in the range of ± 14% on two ventilators studied.ConclusionsDepending on the placement site of the flow sensor in the ventilator circuit, the compliance and resistance of the test lung have different influences on the accuracy of VT delivery, which is further attributed to different fluid dynamics effects of the compliance and resistance. The main influence of compliance is to raise the peak inspiratory pressure Ppeak, thereby increasing the compression volume within the ventilator circuit; whereas a high resistance not only contributes to elevating Ppeak, but more importantly, it governs the gas flow conditions. Ppeak is a critical predictive indicator for the accuracy of the VT delivered by a ventilator.

EXPERIMENTAL INVESTIGATION AND CFD SIMULATION OF THE ORIFICE FLOW METER TO MEASURE TWO-PHASE FLOW

In this study, an investigation is conducted to examine various methods for measuring the two-phase flow of water and air. The two-phase flow loop and its equipment, including the orifice flow meter, were designed and manufactured in accordance with relevant standards. By employing the orifice flow meter in the two-phase flow loop and determining the total mass flow rate of the two-phase flow passing through it, the pressure drop of the orifice flow meter was determined for different values of the flow rate and volume fractions of the water and air phases in the two-phase flow. The Reynolds number of the two-phase flow ranged from 700 to 11000, while the air volume fraction ranged from 10% to 45%. We observed that, for the orifice flow meter, the slope of the discharge coefficient variation in relation to the two-phase flow Reynolds number was higher at low Reynolds numbers, where a laminar flow pattern was established. As the two-phase flow Reynolds number increased, the flow pattern transitioned from laminar to plug flow, resulting in a decrease in the slope. The orifice flow meter under two-phase flow conditions was simulated using computational fluid dynamics (CFD) with different turbulence models. The results indicated that the k-epsilon RNG turbulence model yielded more accurate results compared to other turbulence models. This study provides a foundation for the measurement of two-phase flows in the oil and gas industries.

Numerical Analysis of Spray Evaporation Process in Desuperheater

Abstract The cooling water is sprayed into the desuperheater to regulate the temperature of the superheated steam. Computational fluid dynamics (CFD) was applied to investigate the spray evaporation process in the desuperheater. Discrete phase model (DPM) was applied to describe the gas-liquid two-phase flow characteristics based on the Eulerian-Lagrangian approach. The Rosin-Rammler distribution and TAB model were used for the description of the primary and secondary droplet breakup, respectively. The coupling effect of gas-liquid two-phase, influence of temperature on latent heat, the stochastic collision and coalescence of droplets were considered in the CFD model. The numerical results show good agreement with the plant data. The hydrodynamics and temperature distribution characteristics were analysed. The influence of water mass flow rate and orifice dimensions on temperature distribution and temperature non-uniformity was further investigated. The results indicate that increasing the water flow rate can improve the desuperheating ability, but it will make the temperature uniformity worse. Under the same operating conditions, smaller orifice diameters are beneficial for production of droplets with smaller size, leading to better desuperheating ability.

An improved detached eddy simulation method for cavitation multiphase flow

The evolution of cavitation flow involves intense transient characteristics and complex multi-scale motions, significantly increasing the difficulty and computational cost of solving in separation zones. This study proposes an Improved Detached Eddy Simulation (IDES) method, based on a single-equation eddy-viscosity model, aimed at enhancing the resolution of small-scale cavitation flows. By incorporating the broad-spectrum von Karman scale concept, the method effectively improves the resolution capability for small-scale flows in separated zones. The performance of the IDES model was validated through three computational cases, and the main conclusions are as follows: The results of the triangular cylinder flows show that the IDES model demonstrates a resolution capability for large-scale turbulence comparable to the Large Eddy Simulation (LES) model. The orifice flow results indicate that activating the LES method with insufficient grid resolution is highly discouraged, whereas the IDES model performs more robustly under such conditions. For hydrofoil flows, the IDES model more accurately captures the temporal evolution of cavitation, avoiding the premature cavity shedding predicted by LES under coarse grid conditions. The decomposition results of the vorticity transport equation show that both the dilatation term and viscous term are significant contributors in the vorticity transport process, with their average contributions to vorticity reaching 49.25% and 39.99%, respectively. Vortices can be considered the primary controllers of cavitation dynamics, while the dilatation term and viscous term can be regarded as the main controllers of vorticity. Overall, the energy compensation mechanism of the IDES model, based on local flow information, gives it unique advantages in handling small-scale turbulence and cavitation phenomena, providing both high computational efficiency and accuracy.

Extraction and characteristic analysis of the nonlinear acoustic impedance of circular orifice in the presence of bias flow

The acoustic behavior of the circular orifice is influenced by the bias flow and high amplitude sound excitation. The present study proposes an approach based on the three-dimensional (3D) time-domain computational fluid dynamics (CFD) simulation to extract the nonlinear acoustic impedance of circular orifice. Impact coefficients of the bias flow on the acoustic impedance of circular orifice are defined as the ratio of the acoustic impedance difference between the cases in the presence and absence of bias flow under high amplitude sound excitation to that under low amplitude sound excitation. The effects of bias flow Mach number, orifice diameter, plate thickness, and porosity on the impact coefficients under different amplitude sound excitations are studied, and the impact coefficients could collapse all the predictions by using the non-dimensional sound particle velocity. The fitting formulas of nonlinear acoustic impedance of circular orifice are presented by using nonlinear regression analysis.

Upgrading of the modified Knudsen equation and its verification for calculating the gas flow rate through cylindrical tubes

The modified Knudsen equation was developed to calculate the gas flow rate through a cylindrical tube with arbitrary length-to-diameter ratio in any flow regime including molecular flow, viscous laminar flow, turbulent flow, critical flow, subcritical flow, and their intermediates in our laboratory. Here, it is upgraded for better agreement with literature data, and the upgraded version is compared with 83 literature sources including 31 gas flow equations to verify its reliability. For Kn > 10−5, the modified Knudsen equation mostly agrees with the literature data to within 20%, except for orifice flows with pd/pu ≈ 1.

An improved drift model of dropped containers under wind and current effects

In the face of the increasing risk of Maritime accidents caused by global climate change, it is necessary to improve the accuracy of drift model of the dropped containers at seas for Maritime Search and Rescue (SAR). Sensitivity test on the classic drift model illustrates that immersion ratio (Ir) of container plays a dominate role in the drift trajectory of container compared to the drag coefficients. Inspired from it, a new scheme of variable Ir is proposed to improve the model by considering the water entering process of container in the study. Based on the stability analysis of four floating attitudes of intact empty container under strong wind condition, the variable Ir is estimated according to the orifice inflow theory and the Archimedes' principle of buoyancy. The new scheme is compared with the fixed Ir scheme from the simulation of the drift trajectory of the dropped container at Xiamen Bay of China. The result shows that error arisen from the fixed Ir would be accumulated as the time integral, but the new scheme of variable Ir can obviously improve the model accuracy for the long-time prediction of SAR. In addition, the drag coefficients of wind and water in the drift model of the dropped container are suggested to be 0.8 and 1.2, respectively.

Energy-efficient bubble aeration guided by bubble dynamics model: From bubble formation at submerged orifice to oxygen utilization during uprising

Bubble aeration is a significant consumer of energy in wastewater treatment processes. Optimizing oxygen transfer, from an energy usage perspective, is crucial in the development of clean production techniques and for the stimulation of the circular economy. Although large efforts have been made in enhancing this process, particularly in ameliorating bubble diffusers, a main problem lies in energy wastage due to over-pursuing ultra-fine bubble generation. In this study, a dynamic model, that integrated both bubble expansion and detachment at submerged orifices, and consequential oxygen utilization during the uprising, was developed in order to better facilitate energy savings during the control of bubble generation. We demonstrate through calibrated models that bubble formation is governed by many factors including gas flow rate, orifice radius, surface tension, liquid viscosity, and surface wettability. Small bubbles are more prone to form when subjected to conditions of high wettability, small orifice size and low flow rate, since the bubbles are easily detached by the increasing upward forces in these scenarios. The oxygen transfer during the rising process was calculated as a function of bubble size, gas type and water depth. Bubbles with a radius smaller than a threshold value can shrink and collapse while below the water surface and thus provide 100% oxygen utilization. The threshold values of bubble radius are determined to be 150 μm and 250 μm at 5 m and 15 m initial water depth, respectively. The parameter set for bubble generation in order to obtain the desired bubble size may then be inversely determined by our bubble formation model, and it's considered as optimal aeration strategy to realize precise aeration. With these results, our study highlights the viability of the approach employing the proposed model in order to direct energy-efficient bubble generation.

Three-dimensional simulation of an orifice flow with cavitation-induced air release

A model for the approximation of cavitation-induced air release in three-dimensional flow simulations is proposed. A cavitating orifice flow is investigated. It is assumed that vapor vanishes in the proximity of the orifice, and bubbles further downstream consist essentially of air. The model is based on a homogeneous mixture assumption and comprises one main parameter, which needs to be adjusted to the experimentally measured degassing fraction. Experimental validation is based on transmission light images downstream of the orifice. In the proximity of the orifice, the inclusion of air release in the CFD simulation yields a better agreement to experimentally measured cavitation intensity than the consideration of pure vapor only. It is concluded that a considerably larger amount of air is released than is dissolved in the evaporated amount of liquid. The simulation results suggest that the released air mass corresponds to about 1% of the evaporated liquid mass. These observations may be a good basis for purposeful future experiments, which are indispensable for the development of a more predictive approach of cavitation-induced air release in 3D CFD methods.

Numerical modelling of flow field at shaft spillways with the marguerite-shaped inlets

By decreasing the entrained air flow discharge and improving the hydraulic characteristics of vertical shaft spillways, Marguerite-shaped inlets (MSIs) can mitigate the effects of swirling flow surrounding their inlet. The hydraulic and hydrodynamic characteristics of flow around MSIs under orifice flow regime were numerically investigated, applying different geometrical parameters. This inlet configuration can decrease the strength of swirling flow and increase the flow discharge through the shaft. The finite-volume method and the re-normalisation group k–ε turbulence model were employed to solve the governing equations of motion in a cylindrical coordinate system and a two-phase air–water flow on the water free-surface. Increasing the height and length of the blades of the MSIs was found to increase the area of the barriers against swirling flow, weaken the swirling flow strength, engender a more uniform flow and lower the water free-surface level. Extremely long or high blades, however, resulted in an intense collision of the flow with the spillway and increased the water free-surface level and the swirling flow strength at the MSI.

Vortex–airfoil interaction noise control using virtual serrations and surface morphing generated by leading-edge blowing

Suppression of vortex–airfoil interaction noise from a rod-airfoil model by virtual serrations and surface morphing formed by the leading-edge (LE) blowing was investigated experimentally in an anechoic wind tunnel. The control efficiency of the virtual serrations and surface morphing was evaluated and analyzed by setting different air flow rates (Q), deflection angles (α), and orifice number (M). Noise measurements by far-field microphones show that both can effectively reduce the peak tonal noise generated by the vortex–airfoil interaction, with the control efficiency increasing with the increment of flow rate Q. As for the LE serration, the noise reduction increases with the virtual serration amplitude ratio Av (=Ub/U∞, Ub: blowing velocity; U∞: wind speed), but decreases slightly with the deflection angle α. A reduction of 12–14 dB is obtained when Av = 3.7 and α = 0° or 10°, and there exists a critical amplitude of Av = 1.5, under which no noise reduction is achieved. Compared to the serration at the same flow condition, the virtual surface morphing has much lower control efficiency, with a maximum noise reduction of 3–5 dB. The flow visualization by the particle image velocimetry technique reveals that both build buffer zones in the front of the airfoil LE, preventing the vortices from directly impinging upon the solid LE, thus reducing the intensity of vortex–airfoil interaction. In particular, the virtual serration breaks up the large-scale vortex structure into small-scale vortices, manifesting its high noise control efficiency.

Freight train air brake modelling with emergency valves

The 120-type air brake system is unique around global rail industry and critical for Chinese freight train operation. Existing research about its simulations does not include detailed models for the emergency brake valves. This paper filled this research gap by developing a detailed fluid dynamic air brake system with a focus on the emergency brake valve. The working principle of the emergency brake vale was reviewed. The brake system model was based on gas flow governing equations (mass and momentum) and orifice flow equations. The model was validated by comparing with measured data from a 150-wagon train. Four braking scenarios were compared. The simulated maximum cylinder pressure was only 5 kPa out of the range of the measured data. The maximum difference regarding the time when cylinder pressure reaches maximum pressure was 4 s. The simulation results have also shown variable switch pressure points for the two-stage brake valve. This is agreed by the measured results and was not shown in previously published research.

Discharge coefficient of vertical sluice gates with broad crested weir under free-submerged orifice flows using best subset regression.

Accurate calculation of flow discharge for sluice gates is essential in irrigation, water supply, and structure safety. The measurement of discharge with the requirement of distinguishing flow regimes is not conducive to application. In this study, a novel approach that considers both free and submerged flow was proposed. The energy-momentum method was employed to derive the coefficient of discharge. Subsequently, the discharge coefficient was determined through the experiment which was performed on the physical model of a vertical sluice gate with a broad-crested weir. Feature engineering, incorporating dimensional analysis, feature construction, and correlation-based selection were performed. The best subset regression method was employed to develop regression equations of the discharge coefficient with the generated features. The derived formula was applied to compute the discharge coefficient in the vertical sluice gate and determine the flow discharge. The accuracy of adopted method was assessed by comparing it with recent studies on submerged flow, and the results demonstrate that the developed approach achieves a high level of accuracy in calculating flow discharge. The coefficient of determination for the calculated flow rate is 0.993, and the root mean square percentage error is 5.04%.

Experimental investigation of two-phase flow development through two-stage orifices

In this study, the effect of flow development length on two-stage flow orifices at an intermittent flow condition was investigated. Experiments were carried out for two-stage orifices with area ratio of 0.25–0.14 and with 1, 3, and 5D spacing between orifices. Also, experiments were carried out on single-stage orifices of the same area ratios under the same inlet flow conditions. The data suggested that restricting the flow in stages, with the smaller area of the restriction in the final stage, reduced the flow separation, enhance the mixing and improve flow development downstream as the spacing increased. Also, the total pressure drop of the two-stage orifice found to decrease as the spacing decreased especially at low gas superficial velocity. Finally, a new approach to correlate the total pressure drop was proposed and successfully implemented in order to determine the pressure drop multiplier of two-stage orifice with varying spacing.

Orifice and Fluid Flow Modifications for Improved Damping in Vehicle Suspensions: A Comprehensive Review

Orifice and Fluid Flow Modifications for Improved Damping in Vehicle Suspensions: A Comprehensive Review

Design optimization of noise reduction for labyrinth control valve in secondary circuit flow regulation system

The labyrinth control valve has been widely used in the secondary circuit flow regulation system of nuclear power field for good pressure reduction and cavitation suppression characteristics. The design of the labyrinth channel is a key to realizing pressure regulation and cavitation suppression for the labyrinth control valve. However, an unreasonable labyrinth flow channel design will be challenging to meet the requirements and aggravate the noise problem under severe operating conditions. This paper proposes a hybrid labyrinth flow channel structure (HLS) that combines the traditional labyrinth flow channel (TLS) and orifice plate structure. The cavitation volume and maximum flow velocity are used as evaluation parameters of the labyrinth flow channel noise. The flow characteristics analysis show that compared with the TLS, the HLS can reduce flow velocity, decrease cavitation volume, improve transmission loss, and lower sound power levels. In addition, the influence between the HLS structural parameters and the noise evaluation parameters is clarified by correlation coefficient analysis. A low noise HLS based on the adaptive NSGA-II algorithm is established. The experimental results indicate that the optimized HLS reduces air noise by 4.21 dB(A) compared to the TLS. The optimized HLS can effectively reduce noise, and help the design of low noise labyrinth flow channels for nuclear power field.

Experimental investigation on the impact of air flow rates and back pressures on kerosene microscopic spray characteristics discharged from an air-assisted pressure-swirl atomizer

The air-assisted pressure swirl atomizer has attracted considerable interest owing to its exceptional capacity to generate fine droplets and precisely regulate spray characteristics. The primary objective of the study was to investigate the impact of auxiliary air flow rate, orifice diameter, and ambient back pressure on the kerosene spray cone angle, droplet size and distribution. The results indicate that employing a nozzle with a smaller orifice size leads to a larger spray cone angle. The spray cone angles of the other two orifice sizes exhibit an increasing trend as the auxiliary air flow rate increases. Also, increasing the auxiliary air flow rate effectively reduces the Sauter Mean Diameter (SMD). Additionally, as the auxiliary air flow rate gradually increases, the peak of the particle size distribution shifts towards smaller diameters. Furthermore, as the environmental back pressure increases, there is a noticeable decrease in the SMD. With an increase in ambient backpressure, there is a consistent shift of the peak particle size towards smaller diameters. At an elevated ambient pressure of 1.4 MPa, an increase in the axial distance from the nozzle results in a decrease in the volume percentage of the peak diameter, while simultaneously causing the particle size distribution range to broaden.

A 3D numerical model for the performance analysis of a differential pressure flow meter in transient conditions for liquid fuels

In the present paper, the metrological performance of a single-hole, sharped edge, and the orifice flow meter is numerically investigated employing different liquid fuels. Numerical investigations have been performed for a three-dimensional transient flow. Turbulence has been modeled employing the Realizable K-ε turbulence model, based on the Unsteady Reynolds-averaged Navier-Stokes (URANS). The present work is conducted in the context of the European SAFEST 20IND13 project, aimed at investigating the performance of the orifice flow meter numerical model in a wide range of temperatures, density, viscosity, and different liquid fuels. The numerical model, validated according to the ISO standard 5167-2 is employed to analyze the metrological performance of a test rig available at project partners’ laboratories and was aimed at reproducing the fuel consumption curve of a light and heavy transport vehicle.

An Orifice Flow Analysis on the Basis of Density and Viscosity Effects of Fluids

The orifice flow measurement produces errors due to highly turbulent and backflow in downstream which have to be overcome. Determine the Δp, and coefficient of discharge (Cd) for flow through the orifice CFD analysis. The input parameters vary with the variance of Reynolds number (Re), fluids with the deviation of density and viscosity, area ratio (σ). The range of Re (20000- 100000), σ (0.2- 0.6), density (ρr), and viscosity (µr) ratio vary as per the fluids considered. The various incompressible and compressible fluids are considered for the study of flow through the orifice based on the difference in density and viscosity properties. The fluids considered for studies are Air, Ammonia (NH3), Carbon dioxide (CO2), Hydrogen (H2), and Sulphur dioxide (SO2) as compressible fluid category, and water (H2O), liquid ammonia (LNH3), liquid hydrogen (LH2), liquid oxygen (LO2), liquid R12 (Dichlorodifluoromethane) as incompressible fluid category. Correlations are also proposed from the above numerical database to determine Cd as a function of Re, σ, ρr, and µr for the orifice. The correlation provides a significant contribution to the viscous fluid flow measurement with the flow through the orifice.