Simultaneous measurements of velocity and deformation in flows through compliant diaphragms

Flow through a circular orifice in a deformable diaphragm mounted in a pipe was studied experimentally as a simple yet suitable case for validating numerical fluid/structure interaction (FSI) codes including structures with significant deformation and strain. The flow was characterized using pressure taps, particle image velocimetry (PIV), and hot-film anemometry while deformation of the compliant diaphragm was determined directly from PIV images. The diaphragm material properties were measured independently by a uniaxial tensile testing machine. The diaphragm material modulus, orifice diameter, and pipe Reynolds number were varied over ranges appropriate for simulations of flows through heart valves. Pipe Reynolds numbers ranged from 600 (laminar upstream condition) to 8800 (turbulent upstream condition). The pressure drop across the diaphragm resulted in a concave deformation for all cases studied. For the range of Reynolds number tested, the Euler number decreased with increasing Reynolds number as a result of orifice expansion. The flow immediately downstream of compliant diaphragms was jet-like with strong inward radial velocity components and vena contracta. Laminar low Reynolds number flow (Re=600) through both rigid and compliant diaphragms yielded early and regular roll up of coherent vortex rings at a fixed frequency in contrast to turbulent higher Reynolds number flow (Re=3900), which yielded a broad range of vortex passage frequencies. Expansion of the compliant orifice for Re=3900 resulted in an initially broader slower jet with delayed shear layer development compared with the equivalent rigid case.     

Effects of upstream bends and valves on oriffice plate pressure distributions and discharge coefficients

An extensive series of tests has been carried out to determine the effect of upstream fittings (bends, valves, bend-bend and bend-valve combinations) on the discharge coefficients of orifice plates. The pressure data acquired during these tests have been studied in detail and a number of general recommendations for reducing the errors associated with using orifice plates in disturbed flow conditions are presented in this paper. It is noteworthy that other tapping combinations in place of the standard D and D/2, flange and corner combinations were less sensitive to disturbances in the flow so that their use could result in smaller errors. Of more direct practical use, as the internationally standardized tapping arrangements are unlikely to be changed, it was established that the use of a further pressure measurement would allow the change in the discharge coefficient for corner and flange taps to be estimated with reasonable accuracy for most adverse flow conditions     

On the Hysteresis Phenomenon of Turbulent Lifted Diffusion Methane Flame

This paper reports an experimental investigation on the flow characteristics upstream of a lifted turbulent diffusion flame in the presence of a coflow. Three fuel nozzles made of a long pipe with different outlet geometry were examined. One pair of these nozzles has the same orifice diameter but different normalized lip thickness, and another pair has the same normalized lip thickness but different orifice diameter. The strength of the co-airflow was also varied to assess its impact on the liftoff height of the jet diffusion flame. Previously published studies reported the existence of a hysteresis phenomenon in the liftoff height of a turbulent diffusion flame in the presence of a high co-airflow. That is, as the fuel velocity decreases, the lifted flame base would first move upstream (toward the burner) to a local minima followed by a downstream movement before its reattachment. The results of the present study, however, showed that such a phenomenon does not appear for a fuel pipe having a very small lip thickness. The present results also revealed that in the hysteresis region, the flame base sits where the turbulence intensity experiences its local maxima in the upcoming unburnt mixture. This corroborates the premixed stability theory which is based on turbulence intensity. Based on this, a correlation was found between the flame liftoff height in the hysteresis region and the fuel and co-airflow velocity at the nozzle exit. This relationship predicts successfully the liftoff height trend as a function of the fuel jet and co-airflow velocity and nozzle geometry. Away from the hysteresis region, however, the flame base location tends more toward the outside of the local turbulence intensity maxima. This indicates the limitations of the premixed stability theory in predicting the flame behavior in this region where the effect of the flow large-scale structures becomes important.     

Experimental study of wall curvature and bypass flow effects on orifice discharge coefficients

This paper presents the results of an experimental study investigating the impact of wall curvature and bypass flow on the discharge coefficients of circular orifices. To extend the range of currently available discharge coefficients, the ratio of the orifice to the pipe diameter is varied from 0.25 to 0.67. Functional relationships are developed that relate a free-discharge orifice coefficient to the ratio of the orifice diameter to the pipe diameter and the total head (velocity and pressure heads) upstream of the orifice. In addition, the use of the projected area versus surface area of the orifice for determining discharge coefficients is investigated and the results show that both approaches yield similar observations. The results of this experimental study are particularly useful for the case of sparger design.     

Characteristics of R-123 two-phase flow through micro-scale short tube orifice for design of a small cooling system

We present a new discharge coefficient correction method for the orifice equation for R-123 two-phase flows. In this method, an evaporator is mounted after the orifice as a vapor refrigeration cycle, and the evaporator is used to measure the quality of downstream flow through the orifice. Quality is estimated from the measured temperature and pressure of the evaporator inlet and outlet, respectively, instead of by direct measurement of quality. The condition of upstream flow of the orifice is the liquid state at 3 bar and 60 °C. The liquid flow is changed to two-phase flow after passing through the orifice. Orifice diameters of 300, 350, 400, and 450 μm are used for the experiment, and the results are analyzed. Experiments are conducted for various conditions of flow rate between 20 and 70 ml/min and for cooling loads of 60, 80, and 100 W. The results show that the quality of flow downstream from the orifice can be calculated using the enthalpy difference between the inlet and outlet of the evaporator. An equation to determine the discharge coefficient is formulated as a function of quality. We expect that these results can be used to help design a small cooling system.     

Effects of an upstream inclined rod on the circular cylinder–flat plate junction flow

An inclined rod is installed upstream of a circular cylinder mounted on a flat plate to mitigate the horseshoe vortices in the junction flow. Smoke-wire visualization, hot-wire velocity measurement and surface pressure measurement are employed to study the effects of the inclined rod on the laminar and turbulent junction flows. The results show a properly placed inclined rod can significantly weaken the horseshoe vortices in front of the cylinder, depress the unsteady oscillation of the vortex system, change the separation position on the flat plate and narrow the wake of the cylinder. The inclined rod method provides a promising way to suppress the horseshoe vortices in the junction flow because of its effectiveness and its easiness to implement and adjust to fit different flow conditions.     

An investigation of turbulent developing flow at the entrance to a smooth pipe

An attempt is made to explain the flow regimes at the entry region of a pipe. Developing turbulent flow was examined and three theoretical models were evolved to explain the three most important regimes: the region of flat plate flow, the region of transition from flat plate to pipe flow, and the region of boundary layer interaction. The model for the flat plate flow was based on the velocity power law but experimental data showed that the exponent was not constant as generally assumed. There was good agreement between the theoretical models and the experimental data for the boundary layer development.

A simple empirical formula was obtained from which it is possible to predict the length of the entry region. The onset of the increase in turbulence intensity at the core, which marks the start of transition from flat plate flow to pipe flow, seems to occur at a particular Reynolds number, based on distance into pipe, of about 3.15×10⁶. This figure may vary with inlet flow condition.     

The compressible discharge of air through small thick plate orifices

Summary The choking of nozzles at pressure ratios below the critical has long been understood. Knife edge orifices however do not appear to choke. This can be explained and the variation of discharge coefficient with pressure ratio may be calculated. The present paper is an experimental investigation into the discharge through thick plate orifices when the pressure ratio is in the vicinity of its critical value. A comparison is made with the results of other workers and an attempt is made to explain the discharge characteristics of thick plate orifices.Notation C discharge coefficient - D orifice diameter - P absolute static pressure - T thickness of orifice plate Suffixes c critical pressure - d downstream conditions - i incompressible flow conditions - u upstream conditions     

Asymmetry in transitional pipe flow of drag-reducing polymer solutions

New experimental data are presented and discussed for fully developed pipe flow of shear-thinning, viscoelastic polymer solutions in the transitional regime between laminar and turbulent flow. The data confirm that such transitional flows exhibit significant departures from axisymmetry in contrast to the fully developed pipe flow of Newtonian fluids or both laminar and turbulent flows of such drag-reducing liquids. The azimuthal structure of the asymmetry is investigated together with its axial development and also the velocity fluctuation levels. These data do not lead to an explanation for the asymmetry but do suggest that the influence of the flow geometry both upstream and downstream can be ruled out.     

用平均速度剖面法测量壁湍流摩擦阻力

用IFA300恒温热线风速仪精细测量风洞中不同雷诺数流动条件下的平板湍流边界层近壁区域对数律平均速度剖面．利用平板湍流边界层近壁区域的对数律平均速度剖面与壁面摩擦速度、流体黏性系数等内尺度物理量的关系和壁面摩擦速度与壁面摩擦切应力的关系,在准确测量平板湍流边界层近壁区域对数律平均速度剖面的基础上,测量平板湍流边界层的壁面摩擦阻力．实现了平板湍流边界层壁面摩擦阻力的无干扰或微小干扰测量．该种方法操作简便,不需要在流场中安装测力天平、传感器等复杂的测量装置,不需要对湍流边界层的壁面进行破坏,不会影响湍流边界层壁面附近区域原有的流场条件,是一种切实可行的测量平板湍流边界层壁面摩擦阻力的简便方法．     

Accurate analysis of multicomponent fuel spray evaporation in turbulent flow

The aim of this paper is to perform an accurate analysis of the evaporation of single component and binary mixture fuels sprays in a hot weakly turbulent pipe flow by means of experimental measurement and numerical simulation. This gives a deeper insight into the relationship between fuel composition and spray evaporation. The turbulence intensity in the test section is equal to 10%, and the integral length scale is three orders of magnitude larger than the droplet size while the turbulence microscale (Kolmogorov scales) is of same order as the droplet diameter. The spray produced by means of a calibrated droplet generator was injected in a gas flow electrically preheated. N-nonane, isopropanol, and their mixtures were used in the tests. The generalized scattering imaging technique was applied to simultaneously determine size, velocity, and spatial location of the droplets carried by the turbulent flow in the quartz tube. The spray evaporation was computed using a Lagrangian particle solver coupled to a gas-phase solver. Computations of spray mean diameter and droplet size distributions at different locations along the pipe compare very favorably with the measurement results. This combined research tool enabled further investigation concerning the influencing parameters upon the evaporation process such as the turbulence, droplet internal mixing, and liquid-phase thermophysical properties.     

流体黏性对输流管道运动方程及临界流速的影响

考虑实际流体黏性引起的管内流速非均匀分布,针对层流和两种不同的湍流流态,对理想流体情况下输流管道运动方程中的离心力项进行了修正,得到的修正系数分别为1.333(圆管层流)、1.020(光滑管壁圆管湍流)和1.037～1.055(粗糙管壁圆管湍流).根据修正后的运动方程得到的上述3种情况下的发散失稳临界流速比理想流体流动情况下依次分别低13.4%,1.0%和1.8%～2.6%.流体黏性对输流管道运动方程及临界流速的影响只与流态有关,雷诺数决定流态,而黏性系数通过雷诺数间接起作用.     

Direct numerical simulation of the flow in the intake pipe of an internal combustion engine

The incompressible flow in the intake pipe of a laboratory-scale internal combustion engine at Reynolds numbers corresponding to realistic operating conditions was studied with the help of direct numerical simulations. The mass flow through the curved pipe remained constant and the valve was held fixed at its halfway-open position, as is typically done in steady flow engine test bench experiments for the optimization of the intake manifold. The flow features were identified as the flow evolves in the curved intake pipe and interacts with the cylindrical valve stem. The sensitivity of the flow development on the velocity profile imposed at the inflow boundary was assessed. It was found that the flow can become turbulent very quickly depending on the inflow profile imposed at the pipe inlet, even though no additional noise was added to mimic turbulent velocity fluctuations. The transition to turbulence results from competing and interacting instability mechanisms both at the inner curved part of the intake pipe and at the valve stem wake. Azimuthal variations in the local mass flow exiting the intake pipe were identified, in agreement with previously reported measurement results, which are known to play an important role in the charging motion inside the cylinder of an internal combustion engine.     

A quasi-similarity analysis of the turbulent boundary layer on a flat plate

The partial differential equation of the boundary layer on a flat plate are simplified by using the universal variables for turbulent flow. For laminar flow this gives boundary layer having a finite thickness and a friction coefficient differing by a few percent from the Blasius value. For a turbulent flow a differential equation for the velocity distribution is obtained with a parameter which varies slowly with the streamwise coordinate. The numerical value of this parameter is determined as an eigenvalue of the differential equations giving a velocity profile which evolves as the boundary layer thickens. Numerical calculations using a simple eddy viscosity model gave results in very good agreement with experiment.     

An experimental investigation of pneumatic swirl flow induced by a three lobed helical pipe

This paper presents a discussion of the results and conclusions drawn from a series of experiments conducted to investigate the swirl flow that are generated by a three lobed helical pipe mounted within a laboratory scale pneumatic conveying rig. The experiments employed Laser Doppler Anemometry (LDA) to quantify the strength of the induced vortex formations and the decay rates of the observed downstream swirl flows over a range of Reynolds number in the turbulent regime. Instantaneous point velocity measurements were resolved in three directions across regular measurement grids transcribed across parallel planes located at four distances downstream of the swirl inducing pipe section. The equivalent axial, radial and tangential velocities were subsequently computed at these grids points. The degree of swirl measured across each measurement plane was expressed in terms of a defined swirl number.It was concluded that the three lobed helical pipe gave rise to a wall jet type of swirl whose rate of observed downstream decay is related to the Reynolds number of the upstream flow and the distance downstream of the swirl pipe. The decay rates for the swirl flows were found to be inversely proportional to the Reynolds number of the upstream flow. The swirl pipe was observed to create a redistribution of the downstream velocity field from axial to tangential, accompanied by a transfer of axial to angular momentum. The findings of this paper are believed to improve understanding to assist the selective use of swirl flow within lean phase particles pneumatic transport systems.     

The effects of wall roughness on the separated flow over a smoothly contoured ramp

Experimental measurements address the effects on a turbulent boundary layer of wall roughness on a flat plate and a ramp that produces a separation bubble over the ramp trailing edge. A fully rough flow condition is achieved on the upstream flat plate. The main effect of the wall roughness on the outer layer turbulence on a flat plate is to change the friction velocity. The separation region is substantially larger for the rough-wall case. The rough-wall boundary layer turbulence is less sensitive to the onset of an adverse pressure gradient over the ramp, producing substantially smaller Reynolds stress peaks in upstream flat-plate, wall-unit coordinates.     

Wall shear stress measurement in a turbulent pipe flow using ultrasound Doppler velocimetry

A turbulent boundary layer of a water flow is investigated by means of pulsed ultrasound Doppler velocimetry. The advantage of this method is the acquisition of complete velocity profiles along the sound propagation line within very short time intervals. The shear stress velocity, used for normalizing the velocity profiles, was determined by fitting the profiles to the universal profiles in a turbulent boundary layer obtained from Prandtl's mixing length theory. A coordinate transformation in the near-wall region is proposed to allocate the velocity data to "true" wall distances. From the experimental values of the wall shear stress velocity, the friction factors for a turbulent pipe flow are calculated and compared to the Blasius law. The overall error in measurement was estimated to NJ.4%.     

Quantitative measurement of spatio-temporal heat transfer to a turbulent water pipe flow

A technique using high-speed infrared thermography was applied to measure the spatio-temporal heat transfer to a turbulent water flow in a horizontal circular pipe. The instantaneous distribution of the heat transfer coefficient and its temporal fluctuation was evaluated by solving inverse heat conduction equation of the heated thin-test-surface. As a result, it was demonstrated that the quantitative measurement, not only the time-averaged heat transfer, but also the statistics of the spatio-temporal fluctuation, was possible using this technique. In addition, a unique feature of the spatio-temporal heat transfer was clearly visualized for the turbulent pipe flow, which was dominated by the streaky structure similar to that for the turbulent boundary layer and the turbulent channel flow.     

Experimental investigation of critical pressure ratio in orifices

To determine the value of the critical pressure ratio in orifices, critical mass flow rate of air through straight-bore orifices and knife orifices was measured. The straight-bore test orifices with varying orifice diameters of 4, 7, 10 and 12 mm were installed in a 20-mm pipe. The knife or sharp-edged test orifices with orifice diameters of 10, 15 and 18 mm were installed in a 40-mm pipe. The test orifices with diameter ratio from 0.2 to 0.6 exhibited a constancy of discharge at ratios of the downstream to upstream pressures of less than 0.17, which is considerably lower than the theoretical critical pressure ratio for an ideal nozzle. An empirical expression to calculate the value of the critical pressure ratio, which includes the relevant primary parameters and which fits the data well, is suggested for engineering design purposes.