Sharp-edged Orifice Research Articles

Measuring two-phase flow in geothermal pipelines using sharp edge orifice plates

The measurement of the two-phase flow rate is very important for the geothermal industry. Among the many different measurement techniques available, the orifice plate stands out for its simplicity, low cost, and the ability to provide real time measurements. Several data sets from different geothermal fields in New Zealand, Indonesia, and the Philippines are used to evaluate existing correlations all of which are based on homogenous flow models. Then derive and test a new correlation based on separated flow model with time discrete liquid phase flow for a more accurate measurement of two-phase flow in geothermal pipelines using the orifice plate. The new correlation is now being implemented successfully in New Zealand and other countries.

Effect of vehicle configuration on the performance of a submersible pulsed-jet vehicle at intermediate Reynolds number

Recent results have demonstrated that pulsed-jet propulsion can achieve propulsive efficiency greater than that for steady jets when short, high frequency pulses are used, and the pulsed-jet advantage increases as Reynolds number decreases into the intermediate range (∼50). An important aspect of propulsive performance, however, is the vehicle configuration. The nozzle configuration influences the jet speed and, in the case of pulsed-jets, the formation of the vortex rings with each jet pulse, which have important effects on thrust. Likewise, the hull configuration influences the vehicle speed through its effect on drag. To investigate these effects, several flow inlet, nozzle, and hull tail configurations were tested on a submersible, self-propelled pulsed-jet vehicle (‘Robosquid’ for short) for jet pulse length-to-diameter ratios (L/D) in the range 0.5–6 and pulsing duty cycles (StL) of 0.2 and 0.5. For the configurations tested, the vehicle Reynolds number (Reυ) ranged from 25 to 110. In terms of propulsive efficiency, changing between forward and aft-facing inlets had little effect for the conditions considered, but changing from a smoothly tapered aft hull section to a blunt tail increased propulsive efficiency slightly due to reduced drag for the blunt tail at intermediate Reυ. Sharp edged orifices also showed increased vehicle velocity and propulsive efficiency in comparison to smooth nozzles, which was associated with stronger vortex rings being produced by the flow contraction through the orifice. Larger diameter orifices showed additional gains in propulsive efficiency over smaller orifices if the rate of mass flow was matched with the smaller diameter cases, but using the same maximum jet velocity with the larger diameter decreased the propulsive efficiency relative to the smaller diameter cases.

Dissipation and Cavitation Characteristics of Single-Hole Orifices

The purpose of this work is to study the dependence of the pressure losses through sharp-edged orifices with respect to the most significant parameters and to find an efficient way to check whether cavitation is likely to occur. Computational fluid dynamics was used to simulate the flow through orifices with different geometrical characteristics for various incoming flow velocities. In particular, the diameter ratio was varied between 0.39 and 0.70, the relative thickness between 0.30 and 1.40, and the pipe Reynolds number between 3.85 × 104 and 1.54 × 105. The computed pressure drop coefficient in the region of self-similarity with respect to the pipe Reynolds number was first compared to that obtained from some literature models. Afterwards, the comparison with experimental data revealed that an extended pressure criterion is suitable to predict the presence of cavitating conditions. A dimensionless minimum pressure coefficient was then defined, and its dependence upon the above mentioned geometrical and flow parameters was investigated. Finally, a practical formula for the prediction of cavitation was provided.

A criterion for flow mechanisms through vertical sharp-edged orifice and model for the orifice discharge coefficient

According to the experimental data of the orifice discharge coefficient for the flow through a vertical sharp-edged orifice obtained in the previous study of this work, a theoretical criterion for flow mechanisms of small orifice (viz. thick-walled orifice and nozzle) and large orifice (viz. thin-walled orifice) was proposed based on the ratio of orifice diameter to plate thickness. It can help explain the dissipation of the mechanical energy loss in the flow process for the two flow mechanisms under different operating regimes. The main parameters such as orifice diameter, plate thickness and liquid head were correlated, and a semi-empirical model for orifice coefficient and an empirical model with high precision at the stable region were developed.

On Evolution of Flow Structure and Vortex Dynamics for Right-Angle and Sharp-Edged Orifice Plane Jet

On Evolution of Flow Structure and Vortex Dynamics for Right-Angle and Sharp-Edged Orifice Plane Jet

Mixing and re-entrainment in a negatively buoyant jet

An experimental study of inclined negatively buoyant jets released from a sharp-edged orifice was carried out to better understand the re-entrainment phenomenon, i.e. the mixing of jet fluid with itself instead with external fluid, and how it biases the jet behaviour. Experiments reproducing an orifice in the lateral wall of an outfall pipe on the sea bottom were conducted using light-induced fluorescence. The mean and variance of the concentration field have been determined to study the hydrodynamic features along the jet axis, including turbulent mixing and entrainment as the densimetric Froude number varies. The re-entrainment phenomenon tends to appear as the angle exceeds 75° with respect to the horizontal, and its onset occurs for lower angles as the Froude number increases. The re-entrainment biases the behaviour of the jet trajectory, making it bend on itself, and causing a reduction of both the maximum height and distance at the location where entrainment of external fluid reaches the jet axis.

On the near-field flow structure and mode behaviors for the right-angle and sharp-edged orifice plane jet

The study of flow structures in a sharp-edged and right-angle orifice plane jet was investigated experimentally by means of hot-wire technique and smoke flow visualization. The results indicate that the vena contracta effect depends upon the Reynolds number as well as the geometric configuration of the orifice exit. The vena contracta effect in the sharp-edged orifice plane jet is much significant and to suppress the development of coherent structures. In addition, the sharp-edged orifice plane jet is considered more complexity since two competing initial instability frequencies were found at Re = 10,300 or above. Meanwhile, two types of instability modes exist in the orifice plane jet, i.e. varicose and sinuous mode. These instability modes were observed to depend upon the Reynolds number and geometric configuration of orifice exit as well.

G0600-2-4 衝突噴流群を用いた流路内の流動および熱移動解析(熱工学部門一般講演(2):伝熱(2))

This paper shows the influence of flow behavior of multiple impingement jets on characteristics of heat transfer of narrow spaces. The jets were set a 5×5 nozzles of sharp edged orifice type with D=5 mm in diameter. The jet-to-jet space is 10 mm. The experiments were performed for the separation distance, H, between jet exit and impingement plate ranging from H/D=1 to 3, at Reynolds number 1600〜3300. The time and spatial temperature profiles over the impingement plate were measured using at infrared camera (TVS-8500, Avio) with a two-dimensional array of Indeum-Antimony (In Sb) sensors. To clarify the influence of the flow behavior on heat transfer fields, we visualized a smoke flow field by means of a laser light sheet method (LLS). Based on these experimental data, the relationships between the fluid flow and the heat transfer characteristics were clarified.

Impact of Orifice Length/Diameter Ratio on 90 deg Sharp-Edge Orifice Flow With Manifold Passage Cross Flow

The available information describing the various stages of flow conditions that occur as the flow transitions from noncavitation to cavitation (turbulent flow), supercavitation, and finally separation in sharp-edge 90 deg orifices is extensive. However, although sharp-edge orifices in cross flow represent a significant number of injection schemes inherent in many applications, data for this configuration are sparse or nonexistent. This study is intended to increase the database and understanding of the driving variables affecting the flow in all of these conditions. Tests were carried out in a unique test facility capable of achieving large variations in back pressure, flowrate, and operating upstream pressure. The configuration and test ranges of this study includes orifice length/diameter ratios from 2 to 10, upstream pressures from 7.03 kg/cm2 to 105.1 kg/cm2, orifice/manifold area ratio of 0.028 to 0.082, and manifold cross flow velocity of from 410 cm/s to 1830 cm/s. The results for these small area ratio configurations support two different first order models, one for cavitation and the other noncavitation both in turbulent flow. Under cavitation conditions the discharge coefficient is related to the contraction coefficient and the cavitation parameter to the 1/2 power. In the noncavitation flow regime the head loss is related to the loss coefficient and the dynamic pressure at the orifice exit. Both the head loss and contraction coefficient were found to be a strong function of the ratio of manifold/orifice exit velocity. Equations are provided defining the relationships that allow determination of the contraction coefficient, discharge coefficient, and head loss between the contraction coefficient, as well as the loss coefficient and operating conditions. Cavitation parameter values for cavitation inception, cavitation, and supercavitation are also provided. The potential flow theory was shown to predict the contraction coefficient when upstream (manifold to vena-contracta) losses are minimal.

The whistling potentiality of an orifice in a confined flow using an energetic criterion

Using a two-source method, the scattering matrices of 10 sharp-edged thin orifices are measured under different subsonic flow conditions. The data are analysed in terms of net acoustical energy balance: the potential whistling frequency range is defined as the one associated with acoustical energy production. A Strouhal number describing the maximum whistling potentiality is found to be equal to 0.2–0.35, based on the orifice thickness and the orifice jet velocity. It appears to depend on the Reynolds number and on the ratio of orifice to pipe diameters. Tests are performed to compare theoretically and experimentally the potential whistling frequency to the actual whistling frequency. They are found to coincide within the measurement uncertainty.

The Impact of Manifold-to-Orifice Turning Angle on Sharp-Edge Orifice Flow Characteristics in Both Cavitation and Noncavitation Turbulent Flow Regimes

The approach taken was to analyze the results in a manner consistent with application by design engineers to new and existing applications, while providing some insight into the processes that are occurring. This paper deals with predicting the initiation of cavitation, cavitation impacts on the contraction coefficient (Cc), as well as noncavitation impacts on discharge coefficient (Cd) from L/D of five sharp-edge orifices over a turning angle range between 60 deg and 120 deg. The results show that in the cavitation regime, Cc is controlled by the cavitation parameter (Kcav), where the data follow the 1∕2 power with Kcav, and inception of cavitation occurs at a Kcav of 1.8. In the noncavitation regime for conditions where the cross velocity is 0 the data are consistent with the first order equation relating head loss (HL) to the dynamic pressure where KL is constant and is consistent with in-line orifices. Cross flow has a significant impact on loss coefficient and depends on both the turning angle and manifold inlet to orifice exit velocity ratio.

Estimation of Cavitation Limits From Local Head Loss Coefficient

Abstract Cavitation effects in valves and other sudden transitions in water distribution systems are studied as their better understanding and quantification is needed for design and analysis purposes and for predicting and controlling their operation. Two dimensionless coefficients are used to characterize and verify local effects under cavitating flow conditions: the coefficient of local head losses and the minimum value of the cavitation number. In principle, both coefficients must be determined experimentally, but a semianalytical relationship between them is here proposed so that if one of them is known, its value can be used to estimate the corresponding value of the other one. This relationship is experimentally contrasted by measuring head losses and flow rates. It is also shown that cavitation number values, called cavitation limits, such as the critical cavitation limit, can be related in a simple but practical way with the mentioned minimum cavitation number and with a given pressure fluctuation level. Head losses under conditions of cavitation in sharp-edged orifices and valves are predicted for changes in upstream and downstream boundary conditions. An experimental determination of the coefficient of local head losses and the minimum value of the cavitation number is not dependent on the boundary conditions even if vapor cavity extends far enough to reach a downstream pressure tap. Also, the effects of cavitation and displacement of moving parts of valves on head losses can be split. A relatively simple formulation for local head losses including cavitation influence is presented. It can be incorporated to water distribution analysis models to improve their results when cavitation occurs. Likewise, it can also be used to elaborate information about validity limits of head losses in valves and other sudden transitions and to interpret the results of head loss tests.

A Series Pressure Drop Representation for Flow Through Orifice Tubes

A simple model is developed here to predict the pressure drop and discharge coefficient for incompressible flow through orifices with length-to-diameter ratio greater than zero (orifice tubes) over wide ranges of Reynolds number. The pressure drop for flow through orifice tubes is represented as two pressure drops in series; namely, a pressure drop for flow through a sharp-edged orifice in series with a pressure drop for developing flow in a straight length of tube. Both of these pressure drop terms are represented in the model using generally accepted correlations and experimental data for developing flows and sharp-edged orifice flow. We show agreement between this simple model and our numerical analysis of laminar orifice flow with length-to-diameter ratio up to 15 and for Reynolds number up to 150. Agreement is also shown between the series pressure drop representation and experimental data over wider ranges of Reynolds number. Not only is the present work useful as a design correlation for equipment relying on flow through orifice tubes but it helps to explain some of the difficulties that previous authors have encountered when comparing experimental observation and available theories.

Alternative method to evaluate discharge coefficients. Part 1: Feasibility study

The purpose of the current paper is to demonstrate the feasibility of a new technique whereby mass flowrates, and hence discharge coefficients can be estimated for a range of pipe discontinuities such as poppet valves, throttles, cylinder ports, and orifices. The requirement to directly measure the mass flowrates using a standard conventional steady flow apparatus has been eliminated. As such, flow characteristics were examined during the transient charging or inflow of air, from atmosphere, through a sharp-edged orifice into a partially evacuated cylinder of known volume. In particular, the current study focused on measuring the transient mass flowrates, pressures, and temperatures of air during an inflow test. Comparison between measured gas pressures and temperatures were made with predicted values from an adiabatic and non-adiabatic zero-dimensional inflow model. Mass flowrates calculated from measured cylinder gas pressure data, without heat transfer correction, were shown to be approximately 20 per cent lower, across the full pressure ratio range, than those measured using the mass flow meter. Iterative trial and error techniques were employed to determine the constant and time varying convective heat transfer coefficients needed to correlate the cumulative mass during inflow with the total mass of air, from initial and final cylinder conditions. Heating the cylinder wall to ensure isothermal conditions resulted in an improved correlation between the measured and estimated mass flowrates.

Unsteady natural ventilation at model scale—Flow reversal and discharge coefficients of a short stack and an orifice

Measurements of unsteady flow rates and pressures have been made on a scale model of a building fitted with two openings—a short stack and a sharp-edged orifice. The flow reversal characteristic of the stack is found to be different to that of a longer stack tested in an earlier study. The short stack displays a greater propensity to reversal, which is consistent with its lower inertia. The time-averaged discharge coefficients of both the stack and the orifice have been examined to determine the effects of external flow. It is found that the effects are similar to those observed in an earlier study that used a different experimental approach.

Influence of nozzle geometry on the near-field structure of a highly underexpanded sonic jet

Abstract Detailed near-field structures of highly underexpanded sonic free jets have been investigated with the help of computational fluid dynamics. Two-dimensional, axisymmetric Euler equations have been chosen to predict the underexpanded jets, and the third-order total variation diminishing finite-difference scheme has been applied to solve the system of governing equations numerically. Several different nozzles have been employed to investigate the influence of the nozzle geometry on the near-field structures of highly underexpanded sonic free jets. The results obtained show that the distance from the nozzle exit to the Mach disk is an increasing function of the jet–pressure ratio, which also significantly influences the shape of the jet boundary. The diameter of the Mach disk increases with the jet–pressure ratio, and it is further significantly influenced by the nozzle geometry, unlike the distance of the Mach disk from the nozzle exit. However, such a dependence on the nozzle geometry is no longer found when an effective-diameter concept is taken into account for the flow from a sharp-edged orifice. A good correlation in the diameters of the Mach disk is obtained, so that the near-field structure of highly underexpanded sonic free jets is a unique function of the pressure ratio, regardless of the nozzle geometry.

Turbulent Flow Downstream of a Perforated Plate: Sharp-Edged Orifice Versus Finite-Thickness Holes

In this study, perforated plates with sharp-edged orificed openings and finite-thickness straight openings were applied to produce nearly isotropic turbulence in a wind tunnel. At the same nominal velocity, the orificed perforated plate was able to produce a higher level of turbulence due to the well-defined flow separation from its sharp edge openings. The integral length, L was found to be related to the square root of the turbulence decay coefficient in the power law decay of turbulence kinetic energy, A. The larger A associated with the orificed perforated plate gave rise to a larger L. The corresponding streamwise autocorrelation functions for the two perforated plates behaved differently, confirming the quantitative disparity in L and further indicates some qualitative difference in the large-scale structures generated.

PIV measurements of a turbulent jet issuing from round sharp-edged plate

An experimental investigation is presented of a turbulent jet issuing from a round sharp-edged orifice plate (OP) into effectively unbounded surroundings. Planar measurements of velocity were conducted using Particle Image Velocimetry (PIV) in the near and transition regions. The Reynolds number, based on the jet initial diameter and velocity, is approximately 72,000. The instantaneous and mean velocities, Reynolds normal and shear stresses were obtained. The centerline velocity decay and the half-velocity radius were derived from the mean velocity. It is revealed that primary coherent structures occur in the near field of the OP jet and that they are typically distributed asymmetrically with respect to the nozzle axis. Comparison of the present PIV and previous hot-wire measurements for the OP jet suggests that high initial turbulence intensity leads to reduced rates of decay and spread of the mean flow field and moreover a lower rate of variation of the turbulence intensity. Results also show that self-similarity of the mean flow is well established from the transition region while the turbulent statistics are far from self-similar within the measured range to 16 diameters.

Experimental study of the near field and transition region of a free jet issuing from a sharp-edged elliptic orifice plate

The mixing characteristics in the near field and transition region, the region of interest in most jet mixing applications, of an isothermal, incompressible, free jet of air issuing from a sharp-edged elliptic orifice plate of aspect ratio 2 into still air surroundings have been studied experimentally using hot-wire anemometry and a pitot-static tube. For comparison, some experiments were performed in round jets issuing from a sharp-edged orifice plate and from a contoured nozzle. All the test jets were unforced and the Reynolds number, based on the equivalent diameter of the sharp-edged elliptic orifice plate which was the same as the diameter of the sharp-edged round orifice plate or the contoured round nozzle, was 1.88 × 10 5 . The three components of the mean velocity vector, time-averaged and phase-averaged fluctuating velocity data, autocorrelation coefficients and one-dimensional spectra of the fluctuating velocities and the mean static pressure were measured. The mean streamwise vorticity, mass entrainment rates and the jet half-velocity widths have been obtained from the measured data. The results show that mixing in an elliptic jet issuing from a sharp-edged orifice plate is higher than in round jets and in elliptic jets issuing from contoured nozzles. The near field and transition region of the elliptic jet were deduced to be dominated by the axisymmetric instability mode which triggers the generation of symmetric shear layer structures. The results also show the presence of coherent structures in the near field and transition region of the jet and the effect of these coherent structures on momentum transport in the jet.

External flow effects on the discharge coefficients of two types of ventilation opening

Envelope flow models are commonly used in the design of naturally ventilated buildings. Such models rely on specification of the discharge coefficient, C z , of ventilation openings, such as air vents and chimneys (stacks). Current practice is to make use of values obtained from laboratory tests under still-air conditions. These values may not be appropriate when the ventilation is due to wind, due to the external flow around the opening which is characterized by unsteadiness of both the velocity and pressure fields. Experimental tests have been carried out in a wind tunnel on two types of openings, namely a sharp-edged orifice (flush to the wall) and a long opening (chimney). Using an analytic result for the still-air case and simple dimensional analysis it is argued that the local crossflow velocity ratio, V/ u, is an important parameter for the orifice and the experimental results support this (as do some simple CFD calculations). The experimental results for the sharp-edged opening are similar to earlier work on generally larger openings. For the long opening the effects of external flow are smaller. In particular, the effects are negligible when the outlet of the opening lies in the external flow. Estimates are made of the consequential uncertainties arising in envelope flow calculations for natural ventilation design.