Experimental Investigation Of Flow Characteristics Research Articles

Experimental investigation of flow characteristics around tandem arrangement of triangular and square cylinders

The paper presents an experimental investigation of the flow around two bluff bodies in a tandem arrangement. Two different configurations were investigated. The first one concerns two square cylinders (SS case) whereas in the second setup, a triangular cylinder was used as an upstream object (TS case). Particular attention was devoted to examining the effect of the gap space G between cylinders (from 1 to 6) on the flow structure and dynamics of vortices. The study also includes measurements conducted for single square and single triangular cylinders to show how the second object modifies the flow field. It was found that the wake behind each object is always wider for the SS case regardless of G. When G is less than or equal to 3 for the TS case, the slender body regime is seen in the flow field which for the SS case is normally present for G<1.5. Consequently, distinctive vortex shedding frequencies cannot be distinguished in the gap for the TS case when G≤3. When G≥4, twice as high values of the Strouhal number St are reported in the gap for the TS case compared to the SS case. Downstream the second object, St gradually decreases from ∼0.245 to ∼1.14 with increasing G from 1 to 4 for the TS case, whereas for 5≤G≤6 distinctive vortex shedding frequencies are no longer observed.

Experimental investigation of flow characteristics and performance parameters of a podded aft engine air intake

This experimental study investigates the flow characteristics and performance parameters of a podded intake in aft-engine configuration at the aerodynamic interface plane (AIP), which is a typical configuration of a generic twin-engine regional jet aircraft. A scaled model aircraft with the port side hollow nacelle is equipped with total pressure rakes positioned exactly at the AIP to obtain the total pressure recovery and distortion. Multiple flight configurations (landing, take-off, and climb-out) with varying angle of attack (AoA) and side slip angle (SSA) are considered; attention has been paid to those with undesirable effects to the flow approaching the engine, by deploying flaps, slats, spoilers, and landing gear compartment. The mass flow rate and thus the mach number at the AIP is adjusted by changing the size of the exhaust nozzle. The Reynolds number dissimilarity is partially compensated by transition band application on the fuselage as well as engine inlet.

Experimental investigation of flow characteristics of a jet in low atmospheric pressure conditions on the Tibetan Plateau

The indoor humidity of heated buildings on the Tibetan Plateau can be as low as 5%RH. Indoor air humidification is very important to people's life and health. Due to the low atmospheric pressure on the plateau, the air physical parameters and wet component diffusion characteristics are different from those of standard atmospheric pressure. This paper investigates experimentally the effects of horizontal and vertical wet jets with various initial velocities, pipe diameters, ambient temperatures, and moisture temperatures on the indoor temperature and humidity field. It is shown that low atmospheric pressure will lead to an increase in relative humidity nearly the jet outlet, but the effective moisture delivery distance becomes shorter and the actual moisture load increases. When the same relative humidity is reached, the specific humidity under low atmospheric pressure is about 1.5–2.5 times as that under standard atmospheric pressure. The average relative humidity of jets produced by the ultrasonic humidification source is 10% higher than the evaporative humidification source during the same time. During the actual humidification process, it is necessary to consider the balance between the initial velocity of the jet and the humidification distance and select the jet tube diameter according to the humidification space area. Additionally, choosing a jet with a temperature slightly higher than the ambient temperature can avoid reducing the indoor temperature. This study should be helpful to the plateau humidification jet characteristics and parameter selection.

Numerical and Experimental Investigation of Flow Characteristics in a Fluid Self-Lubricating Centrifugal Pump with R134a Refrigerant

With the rapid development of information technology, researchers have paid attention to the pump-driven two-phase cooling loop technology for data centers, which imposes requirements on the efficiency and size of the pump. A fluid self-lubricating centrifugal pump with R134a refrigerant was developed to reach a higher rotation speed and oil-free system, resulting in a more diminutive size. Due to the high rotation speed and refrigerant pressure approaching saturated vapor pressure, the internal flow characteristics and cavitating characteristics are critical and complex. This paper focuses on the prototype’s head and cavitation performance based on experimental and numerical data. The experiments indicated that the head coefficient of the pump under design conditions is 0.9881, and the pump’s critical cavitation number and breakdown number are 0.551 and 0.412, respectively. The numerical results can predict the head and cavitation with deviations less than 2.6%. To study changing patterns in flow characteristics under the different operating conditions in the refrigerant centrifugal pump, the numerical model based on a modified Sauer-Schnerr cavitation model was built to analyze the distributions of pressure, temperature, relative velocity, and bubble volume across every hydraulic component and different degrees of cavitation, and proposed the influence of the thermal effect on refrigerant cavitating. The cavitating flow characteristics were obtained with the aim of providing guidance for the hydraulic design of a refrigerant centrifugal pump.

Numerical and experimental investigation of flow characteristics in natural gas pipe

To measure the natural gas flow in the natural gas pipeline, a flow measurement method based on a laser Doppler velocimeter (LDV) is proposed, and the flow field in the natural gas pipeline is accurately measured. The flow laws of the flow field in the pipeline are obtained. In this paper, the influence of the jet flow on the flow field in the main pipe during the injection of tracer particles is analyzed by numerical calculations, and the reliability of the calculation is verified by the LDV test. The results show that the influence of the jet on the flow field in the main pipe weakens rapidly within a short distance, which provides good conditions for measuring the flow in the LDV test pipeline. The error between the flow measured by LDV and the turbine standard device is within 0.47%. Meanwhile, the uncertainty of the LDV measurement test system of a natural gas pipeline is evaluated. The system uncertainty is less than 2%, which satisfies the uncertainty requirements of the metering system, verifying the feasibility of the LDV metering flow and providing a reliable basis for the accurate metering of natural gas.

Experimental investigation of flow characteristics over a surface-modified structured torpedo model

The present work aims to improve the aerodynamic performance of navigating objects using bio-inspired surface modification. Inspired by the denticles present over sharkskin, this work investigates the study of a surface-modified structured torpedo model. Different modified surface structures (riblets) are used to study their effect on the drag and flow characteristics. The modified structure placed in the shear layer modifies the flow above as well as behind the torpedo. A detailed flow field is studied using PIV (Particle Image Velocimetry) and CTA (Constant Temperature Anemometry) over the torpedo model. The experiments are performed in a subsonic wind tunnel for the Reynolds numbers (Re) range of 1.02–5.08 × 105, thus covering the laminar-turbulent transition range. The study reveals that riblets structure enhances the momentum flux, thus enabling the surface to reduce drag by suppressing the vorticity generation and reducing the turbulent dissipation. Different turbulent and wake characteristics are measured in the work. The velocity and fluctuation analysis shows the variation in wake width and wake velocity for different cases. The result showed that riblet effectively reduces drag coefficient by 11.7% using an optimal structure. The maximum reduction in formation length of 4.76% is observed at Re 3.05 × 105. The decrease in the formation length reduces the adverse pressure gradient zone and decreases the power requirement. The wake half-width at the 2D downstream location in the streamwise direction shows a reduction of 9% for the drag-reducing case at Re 3.05 × 105. The vorticity reduction is observed in the wake zone of drag-reducing riblets and suggests less dissipation of the eddy. The results show the perspective to improve the current research status by using riblet surface for marine application. The study could effectively reduce drag, thus improving the operating performance by reducing the energy consumption and increasing the speed of the navigating vessel.

Experimental investigation of flow characteristics in a vertical vibration two-phase loop thermosyphon

In this paper, flow characteristics of a two-phase loop thermosyphon under vertical reciprocating vibration are visually investigated with N-pentane as the working fluid. The tests are performed for a heating power range of 20 W to 40 W, the filling ratio of 30 % to 70%, and a 30 m?s-2, 35 Hz vertical reciprocating vibration. The effect of vertical vibration on flow characteristics of the two-phase loop thermosyphon is investigated by comparing the obtained results with those acquired in static, thereby providing a basis for explaining the heat transfer process of two-phase loop thermosyphon under vibration. The results indicate that vertical vibration promotes the rupture of a liquid plug and the transformation of the plug flow to annular flow or wavy flow. Furthermore, the vertical vibration does not change the distribution law of liquid flow velocity in the two-phase loop thermosyphon. However, it will reduce the overheating and flow velocity in the two-phase loop thermosyphon at the start-up. With an increase in the heating power, the influence of vertical vibration on liquid flow velocity is reduced due to continuous disturbance of the working medium in the two-phase loop thermosyphon.

Experimental investigation of flow characteristics over asymmetric Joukowsky hydrofoil weirs for free and submerged flow

Weirs are one of the most common hydraulic structures used to regulate the upstream approach flow depth and measure the flow discharge. The hydrofoil weirs are a type of short-crested weirs that are designed based on the airfoil theory. These weirs have some merits compared to other types, such as a higher discharge coefficient, more stability, better submergence limiting condition, and lower fluctuations of the pressure and the free-surface profile. In the present study, experimental models of hydrofoil weirs with different relative eccentricities, cambers, angles of attack, and upstream slope angles are applied to investigate their hydraulic characteristics under free and submerged flow conditions. The longitudinal profiles of static pressure over different hydrofoil weirs are compared to circular-crested and ogee weirs. The results indicate that the maximum bed negative pressure belongs to the circular-crested weir, and the lowest bed pressure over the hydrofoil and ogee weirs are approximately the same. Applying a hydrofoil weir with an appropriate curvature and angle of attack instead of a circular-crested weir not only increases the structural weir height as well as the upstream water depth but also results in the lowest values of bed negative pressure, thereby reduces the potential of cavitation over the weir body, being safer hydraulic structures. The results also show that the discharge coefficient of hydrofoil weirs is greater than that of the broad- and short-crested weirs for the upstream approach flow depth relative to the weir crest to weir length h1/L > 0.12 and is greater than that of the ogee weirs for 0.35 < h1/L < 0.45. Furthermore, the derived relationships for the discharge coefficient, threshold submergence, and the discharge reduction factor due to submergence accurately predict the hydraulic characteristics of hydrofoil weirs compared to the available developed empirical relationships for these weirs and can be used efficiently for design purposes.

Experimental Investigation of Flow Characteristics in Porous Media at Low Reynolds Numbers (Re→0) under Different Constant Hydraulic Heads

Understanding natural flows in porous media with low Reynolds number (Re) has significant implications for both science and engineering. However, knowledge and experimental gaps remain regarding such natural flows. In this context, we designed a sand column-based laboratory filtration experiment to investigate flow characteristics in porous media with low Re. Four media were considered including two silts (silt-I and silt-II), one silty sand, and one medium sand. Results show that constant hydraulic head is presumed to be an important factor that affects flow regime in porous media. In general, the flow approaches Darcian at a constant hydraulic head of ~170 cm, whereas it becomes non-Darcian at a constant hydraulic head of ~230 cm. The type of media determines the Re range that delimitates between Darcy and non-Darcy flows. Specifically, the transition appears at 0.015 &lt; Re &lt; 0.020 for medium sand and 0.000027 &lt; Re &lt; 0.000029 for silt-II, respectively. In the condition of constant hydraulic heads, the breakdown of Darcy’s law may occur at very low Re values (Re→0). Media dependent Re ranges are probably needed to describe the beginning of non-Darcy flows, rather than 1 to 10 or other value for all media. Findings in this study can offer insights into calculation and simulation of flows in low-permeability reservoirs, pumping process of foundation pit excavation, and other non-Darcy flows in low-permeability media.

Flow characteristic of horizontal-vertical upward air-water with 45° elbow

An experimental investigation of flow characteristics of horinsontal-vertical upward with 45° elbow has been conducted in a ¾ “ inner diameter pipe. The aims of this research are to determine the pattern of two-phase fluid flow (water-air) and pressure drop occurred in the flow. Data were obtained by varying flowrate of 1 – 3 lpm and volumetric proportion of gas (ß) of 25-50%. The results showed that a slug/plug flow was occurred at the 45° with various charateristics. The slug/plug flow indicated more bigger as the gas volume fraction (β) bigger and those are inversely to the supervisial air Reynolds (VSL). The size and the shape of the slug/plug flow were inversely with the pressure drop due to the mixing of two flow of air – water. The higher pressure drop theorically and experimentally occurred at 216.6 Pa and 107.4 Pa respectively on gas volume fraction (β) of 25%, superfisial air speed (vsG) of 0.076 m/s and superfisial water speed (vsL) of 0.227 m/s.

Experimental Investigation of Flow Characteristics of Corrugated Channel Flow Using PIV

Experimental Investigation of Flow Characteristics of Corrugated Channel Flow Using PIV

Experimental investigation of flow characteristics around four square-cylinder arrays at subcritical Reynolds numbers

The Deep Draft Semi-Submersible (DDS) concepts are known for their favourable vertical motion performance. However, the DDS may experience critical Vortex-Induced Motion (VIM) stemming from the fluctuating forces on the columns. In order to investigate the current-induced excitation forces of VIM, an experimental study of flow characteristics around four square-section cylinders in a square configuration is presented. A number of column spacing ratios and array attack angles were considered to investigate the parametric influences. The results comprise flow patterns, drag and lift forces, as well as Strouhal numbers. It is shown that both the drag and lift forces acting on the cylinders are slightly different between the various L/D values, and the fluctuating forces peak at L/D = 4.14. The lift force of downstream cylinders reaches its maximum at around α = 15°. Furthermore, the flow around circularsection- cylinder arrays is also discussed in comparison with that of square cylinders.

Experimental Analysis of Flow Characteristics from Different Circular Nozzles at Plunging Water Jets

A plunging water jet passing through the surrounding air entrains a large amount of air bubbles into a pool and forms a large submerged two-phase (gas–liquid) contacting area. This process is called air-entrainment or aeration by plunging water jets. Numerous studies were conducted with circular nozzles. This paper presents experimental investigation of flow characteristics of truncated and non-truncated circular nozzles. The flow characteristics such as volumetric air entrainment rate, bubble penetration depth and oxygen transfer efficiency are evaluated based on four major parameters which describe air entrainment at the plunge point: the nozzle diameter, jet length, jet velocity, and jet impact angle. In addition, new predictive equations are developed for the flow characteristics of truncated and non-truncated circular nozzles. Experimental results showed that truncated and non-truncated circular nozzles have very different flow characteristics. The truncated circular nozzles indicated a rather high quality with respect to bubble penetration depth, volumetric air entrainment and oxygen transfer. In aeration application, the truncated circular nozzles can be preferred due to different flow characteristics.

An experimental investigation of the flow field between two radial plates

The flow field in a radial diffuser downstream of a radial impeller is highly complex, as the flow is turbulent, unsteady, viscous, and three-dimensional. Depending on the initial conditions at the diffuser inlet, the flow may separate from one or both walls of the diffuser. The objective of this experimental investigation of flow characteristics in a radial vaneless diffuser of a centrifugal blower is to enhance the performance of centrifugal compressors over a wide operating range. Numerical and experimental investigations of rotating stall effects on compressors and blowers have been conducted over the past four decades to achieve this objective. The flow characteristics in a radial diffuser were measured while changing the impeller speed and keeping other parameters such as diffuser radius and width ratio constant. The velocity and pressure distributions in the diffuser were measured along a radial path using a miniature X-wire probe and dynamic as well as static pressure transducers. The axisymmetrical radial and tangential mean velocity distributions and their statistics, as well as pressure distributions, are reported. Some of the results presented in this paper agree with those from earlier work on this subject. For example, the flow angle α (measured at half the diffuser width and from the diffuser inlet to its outlet) did not exceed 65°. This means that α < αc, although a recirculation region was present on the diffuser shroud wall. The critical flow angle αc required to initiate self-excited flow oscillations has been generally reported to be about 78°. Current data also indicate that the flow exiting the impeller is skewed, as revealed by the triple velocity product correlations. The current data are valuable for vaneless diffuser numerical model developers, since there are very limited similar data available in the open literature. The current data support the opinion that the flow separation is not enough to trigger or initiate stall at the diffuser.

An analytical and experimental investigation of flow characteristics generated by rotating porous disk

This paper is concerned with investigations of the gas flow around and in the cell-porous rotating disk. A simple 1D model of gas flow is presented. Usually the cell-porous materials are applied in heat exchangers and stationary filters. On the other hand, peculiarities of the flow revealed under theoretical analysis and some experimental observations demonstrate that rotating porous disks may also be effectively exploited in the shear-force machines for the gas transport purposes.

Experimental investigation of flow characteristics of a magnetohydrodynamic (MHD) duct of fan-shaped cross section

Experiments along with numerical calculations are carried out to investigate the effect of the geometry of the cross section on flow characteristics of a MHD propulsion duct. A fan-shaped cross-section MHD thruster duct is chosen for comparison with a previously investigated rectangular cross section. Measurement of the velocity field is made using LDV (Laser Doppler Velocimetry) system with a fiber-optic cable and pressure distribution is measured with static pressure holes at the bottom surface. Comparison with rectangular cross section shows that the velocity profile is significantly influenced by the geometry of cross section while the axial pressure distribution is not so affected.

Validation of the new fluidization potential technique for ζ potential measurement in the nonlaminar flow regime using spherical particles

A detailed experimental investigation of flow characteristics and their influence on ζ potential measurement by the new fluidization potential technique is presented. The governing equation of this technique derived from the classical Helmholtz-Smoluchowski streaming potential equation assumes laminar flow through a steady-state uniform solid-liquid fluidized bed. The results from model suspensions of Ballotini glass spheres (82–280 μm) in deionized water show that a transition from laminar to nonlaminar flow may occur in some fluidization potential tests. Especially with the large size spheres (200–280 μm), fluidization potential measurements have taken place entirely in the nonlaminar flow regime. It was found that the hydrodynamic flow transition does not affect the ζ potential observed from the fluidization potential gradient in relation to volumetric fraction of solids, c within the limits of linearity (0 < c < c max) of the governing equation. c max was the limit of linear dependence of the governing equation and its value up to 0.304 was observed.

Experimental investigation of flow characteristics and thermal accomodation in neutralizer gas cells: Johann L Hemmerich,J Vac Sci Technol, 21, (1), 1982, 86–90.

Experimental investigation of flow characteristics and thermal accomodation in neutralizer gas cells: Johann L Hemmerich,J Vac Sci Technol, 21, (1), 1982, 86–90.

Experimental investigation of flow characteristics and thermal through a tube under free molecular conditions: Christine M Davies and C B Lucas,J Phys D: Appl Phys, 16 (1), 1983, 1–16.

Experimental investigation of flow characteristics and thermal through a tube under free molecular conditions: Christine M Davies and C B Lucas,J Phys D: Appl Phys, 16 (1), 1983, 1–16.

Experimental investigation of flow characteristics and thermal accommodation in neutralizer gas cells

We have performed conductance measurements on 1/10 scale models of typical neutralizer gas cells, both round (32 mm i.d.×163 mm length) and rectangular (20×50 mm cross section×95 mm length). The gas inlet temperature was kept constant at room temperature (295 K), while the duct models were temperature variable (from 77 to 700 K). It could be shown that (1) the gas fully thermally accommodates to duct wall temperature; (2) under typical operating conditions, i.e., for gas target thicknesses from 3×1015 to 1×1016 molecules per cm2, the flow characteristics are dominated by the temperature dependent viscous component. An empirical relation describing the temperature dependence is given. A consequent application of the effects observed leads to improvements in neutralizer performance: if, e.g., a section cooled to 77 K is followed by a section heated to 700 K, the gas flow required for a given gas target thickness is about a factor of 3 lower compared to both sections being at 300 K.