Rectangular Orifice Research Articles

Stepwise conversion of a 10‐membered diketo open‐cage [60]fullerene to a 10‐membered keto‐lactone open‐cage [60]fullerene

The chemical reactivity of a 10‐membered diketo open‐cage fullerene C60(O)2(OOtBu)4 was investigated in an effort to reveal the unique reaction pattern of fullerene derivatives. Selective cleavage of peroxo O‐O bonds was observed under thermolysis in the presence of iodine to form epoxy groups around the orifice. Opening of the epoxy groups leads to vicinal diol moiety, oxidation of which resulted in a new 10‐membered keto‐lactone open‐cage fullerene derivative. Single crystal X‐ray diffraction analysis showed that the size of the rectangular orifice is around 2.96´4.66 Å.

Research on the Throttling Performance and Anti-Erosion Structure of Trapezoidal Throttle Orifices

The throttling performance of conventional throttle orifice structures of fluid control valves is very low. Therefore, this paper proposes a novel trapezoidal throttle orifice with excellent throttling performance. The effect of the taper of the throttle orifice on the erosion was researched. Firstly, two schemes of trapezoidal throttle orifice were proposed according to the fluid control valve. Secondly, the excellent throttling performance of the trapezoidal throttle orifice was compared and optimized. Finally, a numerical simulation method of the erosion-resistant ability of the trapezoidal throttle orifice was established. It was found that for the same throttling area, the differential pressure of the trapezoidal orifice was higher than that of the conventional rectangular orifice by about 18.6%. The taper had little effect on the gas production, which increased by only 3.3% during the 10° to 30° change. The maximum erosion was firstly reduced and then increased with increases in the angle from 0 to 25°of the taper. Moreover, the minimum was achieved at about a 20° taper angle. The above research methods provide a theoretical basis for optimizing the size and structure of orifices and the sealing reliability of fluid control valves.

EXPERIMENTAL STUDY OF DELAYING THE STALL OF THE NACA 0020 AIRFOIL USING A SYNTHETIC JET ACTUATOR ARRAY WITH DIFFERENT ORIFICE GEOMETRIES

An experimental study on the effect of active flow control using a synthetic jet mechanism on stall delay for the NACA 0020 airfoil is conducted. The experiments are carried out at an open-suction type wind tunnel at Reynolds number 5x104. In the presented experimental study, aerodynamic force measurements of the airfoil with having different orifice geometries (cylindrical, rectangular, sinusoidal, v-type, inclined rectangular) are examined by using a speaker type actuator in synthetic jet mechanism. It is observed that all different orifice geometries are effective in delaying the stall angle of NACA 0020 airfoil. However, it is observed that the inclined rectangular type of synthetic jet geometry is the most advantageous in delaying the stall of the airfoil. The effects of geometric parameters of the actuator on lift and drag coefficient of the NACA0020 airfoil are investigated. Experimental results show that among the all-orifice geometries the rectangular orifice geometry is the most effective in increasing lift coefficient of the airfoil. It is observed that there is a maximum decrease in drag at 10⁰ where the stall occurs. In addition, the decrease in drag is observed after 10 in rectangular, v-type and inclined rectangular orifice geometries.

Study of Orifice Design on Oleo-Pneumatic Shock Absorber

Aircraft oil-strut shock absorbers rely on orifice designs to control fluid flow and optimize damping performance. However, the complex nature of cavitating flows poses significant challenges in predicting the influence of orifice geometry on energy dissipation and system reliability. This study presents a comprehensive computational fluid dynamics (CFD) analysis of the effects of circular, rectangular, semicircular, and cutback orifice profiles on the internal flow characteristics and damping behavior of oleo-pneumatic shock absorbers. High-fidelity simulations reveal that the rectangular orifice generates higher damping pressures and velocity magnitude than those generated by others designs, while the semicircular shape reduces cavitation inception and exhibits a more gradual pressure recovery. Furthermore, the study highlights the importance of considering both geometric and thermodynamic factors in the design and analysis of cavitating flow systems, as liquid properties and vapor pressure significantly impact bubble growth and collapse behavior. Increasing the orifice length had a negligible impact on damping but moderately raised orifice velocities. This research provides valuable insights for optimizing shock absorber performance across a range of operating conditions, ultimately enhancing vehicle safety and passenger comfort.

Gas–liquid twin-fluid atomization from non-circular orifices

Passive control of twin-fluid atomization can be achieved by changing the orifice shape of the injector. In this study, the characteristics of twin-fluid atomization in the outside-in-liquid injector with circular, square, and rectangular orifices at various aspect ratios were investigated experimentally and computationally. The morphology of the spray was captured by shadowgraph, the diameter and velocity of the droplets were measured by the phase Doppler particle analyzer, and numerical simulations were performed for the central gaseous core. Comparing the sprays with square and circular orifices, droplets from the non-circular orifice are generally smaller with less disparities in droplet sizes due to the more intensive turbulent disturbances and corner effect. Furthermore, the non-circular orifice also results in better spatial distribution of the spray. The droplet diameters of the spray with a square orifice do not satisfy the log-normal distribution near the orifice along the centerline of the spray, which may be attributed to the different entrainment of spray droplets by the central gas flow for the sprays with circular and non-circular orifices. The twin-fluid sprays produced by the rectangular orifice also exhibit the same axial switching effect as in the high-pressure gaseous jet flow, in which the spray diffusion in the minor axis is more extensive than that in the major axis. Moreover, the droplets' Sauter mean diameter produced by the rectangular orifice is more sensitive to the size in the minor axis of the orifice and decreases as the aspect ratio of the orifice increases given the same cross-sectional area.

Discharge characteristics of lateral rectangular orifice intakes in open channel flow

Discharge characteristics of lateral rectangular orifice intakes in open channel flow

Noise and Jet Momentum of Synthetic Jet Actuators with Different Orifice Configurations

Sound pressure levels and flow characteristics of a synthetic jet actuator (SJA) are investigated experimentally using the following orifice configurations: a) a slender rectangular slot orifice and b) an array of circular orifices with two different orifice diameters. All configurations have similar total orifice neck area, orifice height, and cavity volume, resulting in a similar Helmholtz frequency. Experiments are conducted for orifices mounted on a flat plate under a quiescent condition. The mean jet velocity exhibits resonant peaks at several excitation frequencies, which also gave rise to the sound pressure levels. The resonant frequencies and peak jet velocities were found to depend on the excitation amplitude and orifice configuration. Investigation of the jet momentum penetration into the quiescent air above the different orifice configurations shows that the momentum issuing from the rectangular slot decays much quicker than that of the circular orifices, irrespective of whether the SJA is excited at resonance or not. The most favorable performance (i.e., the highest momentum in the jet core) was obtained with the array of circular orifices having a smaller orifice diameter, even at off-resonance excitations. The work herein shows the possibility of reducing the SJA noise by 8–10 dB by operating the SJA at a frequency away from the Helmholtz frequency while still achieving comparable levels of jet momentum penetration into the crossflow.

Adaptive Toolpath Generation for Material Extrusion Additive Manufacturing Using a Nozzle with Rectangular Orifice

Material Extrusion Additive Manufacturing has greatly simplified the production of complex designs, but it is often accompanied by a trade-off between build resolution and build rate. A higher build resolution can improve the quality of the finished product, but it also slows down the production process. This compromise can be fine-tuned between production runs via alternative sizes of the primary manufacturing tool (i.e., the nozzle), but, in-process reconfiguration of the nozzle is not utilized in the usual Fused Filament Fabrication (FFF) applications. An extrusion system featuring a rotatable rectangular-orifice nozzle can be employed to tune the build resolution. The effective size of the extrusion can be altered through rotational guidance, where a single nozzle acts as if it possesses various orifice sizes. This method holds the potential to introduce variable bead width and height in the process by employing intermediate orientations of the rectangular cross-section. Nevertheless, the implementation of this concept necessitates the development of a customized tool path planning approach. This paper presents methods for planning the trajectory and spin of a rectangular-orifice nozzle to effectively control the position and width of the printed trace. The intention is to promote rapid extrusion of interior regions and enable the printing of finer details with more accuracy. Due to the critical nature of shell manufacturing and infill generation in FFF, dedicated modes of operation have been developed for these tasks. Versatile test cases are developed for the purpose of evaluating the introduced strategies. The results of these test cases demonstrate the applicability of the proposed method for achieving controllable resolution in FFF.

A hybrid ensemble machine learning model for discharge coefficient prediction of side orifices with different shapes

Side orifices are widely applied for flow control and regulation in channel systems. Accurate estimation of the discharge coefficient of the side orifice is significant for water management. The main objective of current research is to accurately predict the discharge coefficients of circular and rectangular side orifices. Considering that traditional empirical regressions are hard to estimate the discharge coefficient precisely due to the complex nonlinear relationship between the discharge coefficient and relevant parameters, a new hybrid boosting ensemble machine learning model, BO-XGBoost, is developed, which combines the advantages of the boosting ensemble model (XGBoost) and Bayesian Optimization. To further evaluate the proposed hybrid model, it is also compared with other tree-based machine learning models, including standalone XGBoost, Random Forest (RF) and Decision Tree (DT). Literature experimental data of the flow and geometric parameters relevant to the discharge coefficients of circular and rectangular side orifices are collected and applied to develop the models. Four dimensionless parameters of the relative channel width (B/L), the relative bottom height (W/L), the relative upstream depth (Y/L) and the upstream Froude number (Fr) are taken into consideration for the prediction of discharge coefficient (Cd). Furthermore, four different input combinations are designed and then compared to determine the best one on the basis of RMSE. By using the optimal input combination, our results demonstrate that BO-XGBoost provides the best comprehensive performance among all the involved machine learning models in the discharge coefficient prediction for both types of side orifices. Besides, the uncertainty analysis also reveals that BO-XGBoost shows the narrowest uncertainty bandwidth and gives the highest prediction reliability.

Measurement and modeling of uniaxial and planar extensional viscosities for linear isotactic polypropylenes

In this work, novel rectangular and circular orifice (zero-length) dies were used to measure planar and uniaxial extensional viscosities as a function of strain rate for various linear isotactic polypropylene melts by using Cogswell methodology. The obtained experimental data were combined with shear and uniaxial extensional viscosity data determined at very high strain rates. The ability of the molecularized generalized Newtonian fluid (mGNF) [M. Zatloukal and J. Drabek, “Generalized Newtonian fluid constitutive equation for polymer liquids considering chain stretch and monomeric friction reduction for very fast flows modeling,” Phys. Fluids 33(8), 083106 (2021)], Giesekus, and explicit Yao constitutive equations to describe the measured data was tested. It has been shown that including the effect of the chemical environment (i.e., the role of the oligomeric solvent) using a simplified version of the mGNF constitutive equation (instead of the commonly used Newton's law) can significantly improve the ability of the Giesekus and Yao viscoelastic constitutive equations to describe the measured experimental data, especially at very high strain rates with using adjustable parameters with a clear physical meaning.

Discharge Through a Vertical, Rectangular Orifice

In this paper, the derivation of a formula is presented to determine the time taken for the discharge of an open tank through a vertical, rectangular orifice. This formula allows a simpler and more accurate determination of the discharge time.The formula obtained by the integration of velocity distribution was checked using a numerical model. It is shown the great correspondence between the derived formula and a formula for small orifices, regardles of whether the orifice is small or not, except in the cases where the height of orifice is much greater than the height of water level from the upper edge of the orifice. The presented formula takes into account the velocity distribution down the orifice and can be treated as a formula for all rectangular orifices.

Design of pintle injector using Kerosene-LOx as propellant and solving the problem of pintle tip thermal damage in hot firing test

The pintle injector is considered to have high reliability because it can control engine thrust by adjusting propellant flow rate via adjusting the orifice area and is strong against combustion instability. Although many studies have been conducted on pintle injectors, their accessibility is limited and studies on performance optimizations for propellant type and propellant mixing efficiency according to pintle shape and atomization are incomplete. In this study, a 1.5-tonf class liquid–liquid pintle injector with rectangular two-row orifices that uses kerosene/liquid oxygen as the propellant was designed and manufactured. Combustion tests were performed on the pintle injector to verify performance and stability under supercritical conditions, which are the actual operational conditions of liquid rocket engines. From the combustion tests on the initial prototype, the pintle tip was observed to be damaged by heat, so the pintle injector design was changed, and thermal fluid analysis was performed to analyze the pintle tip cooling and combustion performances. To increase the cooling performance of the pintle tip, we devised a method of changing the shape of the pintle orifice and inserted a cooling device called an insert nozzle into the pintle without material changes or applied coatings, as in previous studies. The thermal fluid analysis results showed that there was a difference of up to 147–400 K in the pintle tip cooling performance depending on the insert nozzle and blockage factor, which was verified through combustion tests. The characteristic velocity efficiency and heat flux showed increasing tendencies with increase in total momentum ratio, and a difference of up to 2.0% was confirmed for the characteristic velocity efficiency.

Characteristics of waves generated by submerged jets from rectangular orifices

Submerged offset jets are common in drainage systems, slot fishways, and hydraulics engineering. Surge usually occurs at the free surface downstream of the jet, which may affect the downstream shipping in serious cases. However, the properties of this wave are very different from those of stormy waves. The research results of wave characteristics in the ocean cannot be directly applied to the analysis of hydraulics engineering downstream channels. To analyze the water wave propagation characteristic generated by submerged jets from rectangular orifices, a series of experiments are conducted in this paper. The time-history information of free-surface wave along the propagation path under various upstream water depths was measured, and the Hampel filter combined with wavelet threshold filter was used for data processing. The propagation characteristics of submerged jet water waves in the time domain and frequency domain were obtained. The results indicate that: (i) the data processing method adopted in this paper can reduce the error in data analysis; (ii) the wave height of each measuring point approximately conforms to Weibull distribution. With the rise of upstream water depth, the wave height of each measuring point increases gradually, and the wave height decreases exponentially along the propagation path; (iii) the spectrum analysis shows that the peak and width of the spectrum vary along the propagation path. The relevant research results obtained in this paper further reveal the propagation characteristics of water waves generated by submerged jets and enrich the research content of the jet theory.

Effect of orifice shape on impinging synthetic jet

The present experimental study investigated the synthetic jet flow characteristics issued from four different orifice shapes (Re = 4739–5588). The flow dynamics of the jet is examined using the particle image velocimetry technique for circular, rectangular, square, and elliptical orifice shapes and two different surface spacings (z/d = 3 and 8). The results are presented in terms of streamwise distribution of velocity, normal stress, and shear stress. Furthermore, the most dominant modes of higher energy containing structures are obtained using proper orthogonal decomposition and compared for different orifice shapes. The results show that for a lower nozzle to surface spacing, vortices formed in the wall jet from the elliptical orifice contain higher energy than the other orifice shapes. The higher energy-containing vortices cause a delay in attaining self-similarity. Therefore, the self-similarity in the wall jet for the elliptical orifice is delayed than that of the other orifice shapes. Also, the elliptical orifice shape has relatively higher normal and shear stresses than that of other orifice shapes. The elliptical orifice shows 30% and 17% higher crosswise normal and shear stress than that of the circular orifice, respectively. However, for the larger nozzle to surface spacing, the least dominant mode of the structure is observed for the rectangular orifice shape, which results in a shifting of the self-similarity location toward the stagnation point. The findings from the present work are used to explain the variation of the heat transfer rate from a synthetic jet having different orifice shapes and impinging at different surface spacings.

Computational evaluation of air jet cooling from a perforated air ducting system to mitigate heat stress of cows in free stalls

Alleviating the heat stress suffered by dairy cows in order to increase their productivity depends on an effective ventilation system. For this reason, this study evaluated the heat mitigating performance of a perforated air ducting (PAD) system with special attention given to significant design parameters (e.g., the shape and size of the orifices and the speed and flow rate of the air jets) having to do with the jet flow pattern and its corresponding cooling efficiency. More specifically, this work aimed to evaluate, using numerical simulation, the effects produced by four different types of air-jet orifice (i.e., three-circular orifice, single-circular orifice, rectangular orifice, and slot orifice) and also the effects produced by different jet flow rates and by the bulk movement of indoor air with respect to the jet properties and their cooling performance in relation to cows reclining in free stalls. The outcomes show that the jet emitted from the slot orifice distributes air more effectively over the surface of a reclining cow and produces a more even range of skin temperatures. The jet cooling performance achieved with a jet flow rate of 470.4 m3 h−1 (50% of the recommended ventilation rate for 625 kg cow) and a jet temperature of 28 °C was equivalent to the cooling performance achieved by a 2 m s−1 wind stream of the same air temperature passing over the model cow’s body. Additionally, the convective heat dissipation rate of the reclining cow increased from 63.47 to 91.27 W m−2 as the jet flow rate increased from 212.0 to 564.5 m3 h−1, indicating that increasing the flow rate of a jet emitted through the slot orifice could improve the convective heat dissipation rate, but the rate of the increase in the convective heat transfer decreased simultaneously. The bulk movement of the indoor air (>0.2 m s−1) negatively affects jet flow and the corresponding cooling performance. Therefore, a PAD system equipped with slot orifices will most likely be more effective when atmospheric conditions are less agitated (such as those in naturally ventilated barns with minimal cross wind speeds or inside enclosed barns). In short, the findings of this study should warrant using the PAD system to ventilate free-stall dairy barns to mitigate heat stress of dairy cows.

Experimental investigation on flow characteristics and unsteady heat transfer of noncircular impinging synthetic jets

This study investigates the flow characteristics and unsteady heat transfer of noncircular synthetic jets impinging on a heated plate. Thermographic phosphor thermometry and time-resolved particle image velocimetry are used to acquire quantitative wall temperature and flow field information, respectively. At a constant orifice-to-wall distance (H/De = 7.5), five orifice configurations (circular, square, elliptic with aspect ratio (AR) of 3, and rectangular with ARs of 3 and 5) are examined at a wall temperature of 80 °C. The orifice configuration has a significant effect on the heat transfer and vortex behavior of the impinging synthetic jets. The square orifice displays better stagnation cooling performance with 42% increase in the maximum stagnation cooling coefficient relative to the circular case due to the larger impinging velocity and deeper penetration into the wall shear layer. Axis-switching of the vortex rings is detected for both the elliptic and rectangular orifices before they impinge onto the wall. The axis-switching enhances the near-wall mixing and turbulent kinetic energy in the elliptic and rectangular orifices, and thus heat transfer compared with the circular case. Additionally, stronger vortices and deeper penetration into the wall shear layer are observed in the major-axis plane than in the minor-axis plane, leading to enhanced heat transfer in the major-axis direction. In particular, the rectangular orifice with an AR of 5 induces strong secondary structures in the trailing jet following the primary vortex ring, and these are responsible for the double-peak distribution of wall temperature in the major-axis direction. This is the first time a double-peak temperature distribution has been reported for noncircular impinging synthetic jets. The rectangular orifice with an AR of 5 also yields a larger cross-stream velocity in the minor-axis direction, indicating a stronger wall jet. Thus, among the cases considered in this study, the rectangular orifice with AR = 5 achieves the optimal cooling performance and the maximum time-averaged cooling area reaches more than 14 times the jet orifice area.

Analytical Models for Determining the Propagation of Rectangular Surface Jets for Fishway Attraction Flow

The present paper evaluates suitability of two analytical models to determine the propagation of rectangular surface jets as a tool to design fishway attraction flow. It focuses on rectangular orifices of vertical slot fishways with aspect ratios (width-to-height) for W/H < 1. Both models were rewritten to match boundary conditions for fishways because they were initially derived for horizontal orifices. As the basis for the evaluation, the output of the analytical models to RANS simulations for 12 geometries 1/16 <= W/H <= 4 is compared. Applied analytical equations for half-lengths for cases W/H >= 4 are within 5 % of RANS modeling results for all cases. The location of centerline transition locations from analytical models also agree reasonably well with RANS modeling. The findings support efficient design of optimum attraction flow propagation using simple, rapid analytical approaches.

流速と音圧と角部形状による共鳴器開口部の音響抵抗の変化

Acoustic resistance of the rectangular orifice of a resonator attached on a duct was measured. Four types of resonator orifices with different corner shapes were used. To express acoustic resistance as a linear sum of bias flow velocity, grazing flow velocity, and particle velocity in the neck of the resonator, we classified the measured resistance data in two regions dominated by sound pressure and grazing flow velocity, respectively. The acoustic resistance is approximated by the larger value of the linear sum in good agreement with experimental results. The dependence of the acoustic resistance on the Strouhal number was also examined. The variation in acoustic resistance due to vortex shedding at similar orifice corner shape shown by Moers was clearly reproduced.

Flow Characteristic of a Cavitating Jet Issuing from a Small Rectangular Orifice

This study focused on the nature of a cavitating jet issuing from a small rectangular orifice the same size as a control port in a water hydraulic spool valve. The aspect ratio of the jet exit was varied to investigate the cavitation jet behavior. The flow characteristics for each aspect ratio were measured, and the jet behavior was observed with a high-speed camera. The flow characteristics of cavitating jets are changed with the aspect ratio and cavitation number. The larger aspect ratio orifice shows a higher flow rate and larger cavitation number of inception. Visualization of a cavitating jet shows that the behavior of cavitation bubbles depends on the aspect ratio. The cavitating jet region is maintained to the same dimensionless position for all aspect ratios. In addition, the distribution and time history of luminance of the visualized images for each aspect ratio shows that the cavitation generates stably in the jet shear layer.

An Experiment on Flashing-Spray Jet Characteristics of Supercritical CO2 from Various Orifice Geometries

Supercritical CO2 pipelines usually are used to link the CO2 capture system to the geological storage. There are severe hazards once the asphyxiating gas leaks from the long-distance pipeline. The uncertainty of near-field jet characteristics results in imprecise consequences assessment of accidental release of supercritical CO2. To improve the prediction of consequences of accidental release accuracy, the near-field mechanisms of flashing-spray jet was investigated. In this work, an experimental setup with multiple measurement instruments was developed to impose controllable CO2 release from a high-pressure vessel. The flashing-spray jet structures of supercritical CO2 from circular and rectangular orifices were recorded by a high-speed camera. Results indicate that the near-field structures of supercritical CO2 jet from circular and rectangular orifices are totally different, which causes the different dispersion consequences. The jet angle and shock waves were analyzed quantitatively. Lastly, the models of flashing-spray based on the two different phenomena from rectangular and circular orifices were discussed. The combination of macroscopic and microscopic data in the jet can help to understand the complex physics and improve discharge and dispersion model. This work provides a fundamental data to consequences assessment of accidental release of supercritical CO2.