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.     

Heat transfer to air–water annular flow in a horizontal pipe

Two-phase air–water flow and heat transfer in a 25 mm internal diameter horizontal pipe were investigated experimentally. The water superficial velocity varied from 24.2 m/s to 41.5 m/s and the air superficial velocity varied from 0.02 m/s to 0.09 m/s. The aim of the study was to determine the heat transfer coefficient and its connection to flow pattern and liquid film thickness. The flow patterns were visualized using a high speed video camera, and the film thickness was measured by the conductive tomography technique. The heat transfer coefficient was calculated from the temperature measurements using the infrared thermography method. It was found that the heat transfer coefficient at the bottom of the pipe is up to three times higher than that at the top, and becomes more uniform around the pipe for higher air flow-rates. Correlations on local and average Nusselt number were obtained and compared to results reported in the literature. The behavior of local heat transfer coefficient was analyzed and the role of film thickness and flow pattern was clarified.     

Effect of surfactants on liquid loading in vertical wells

Most gas wells produce some amount of liquid. The liquid is either condensate or water. At high rates, the gas is able to entrain liquid to the surface; however, as gas well depletes, the liquid drops back in a gas well (called liquid loading) creating a back pressure on the reservoir formation. Addition of surfactants to the well to remove liquid is one of the common methods used in gas wells. Liquid loading in vertical gas wells with and without surfactant application was investigated in this study. Anionic, two types of amphoteric (amphoteric I and amphoteric II), sulphonate and cationic surfactants were tested in 2-inch and 4-inch 40-feet vertical pipes. Pressure gradient and liquid holdup are measured. Visual observation with a high speed camera was used to gain insight into the direction of foam flow in intermittent flow and foam film flow under annular flow conditions.Liquid loading is initiated when the liquid film attached to the wall in annular flow starts flowing downwards. Introduction of foam causes the gas velocity at which film reversal occurs to decrease; this shift increases with increasing surfactant concentration and it is more pronounced in 2-inch pipe than in 4-inch pipe. That is, the benefit of surfactants is much more pronounced in 2-inch pipe than in 4-inch pipe. The reason for postponement of liquid loading is reduction in the liquid holdup at low gas velocities which reduces the liquid holdup in foam flow compared to air-water flow. However, at higher gas velocities, the pressure drop in 2-inch compared to 4-inch pipe increases rapidly as the surfactant concentration increases. The selection of optimum concentration of the surfactant is a balance between the reductions in the gas velocity at which liquid loading occurs compared to increase in the frictional loss as the concentration increases. We provide guidelines about the selection of the surfactant concentration.Visual observations using high speed camera show differences in the behavior under foam flow conditions. Unlike air-water flow, the liquid film attached to the wall is replaced by thick foam capturing the gas bubbles. The type of roll waves which carry the liquid in 2-inch pipe is different than what was observed in 4-inch pipe. Compared to 4-inch pipe, the roll waves in 2-inch pipe are much thicker. This partly explains the differences in 2-inch versus 4-inch pipe behavior.     

Wave regimes of ascending flow of a thin layer of a viscous liquid in contact with a gas

The flow of a liquid in thin layers is one of the hydrodynamic problems of chemistry and heat engineering. The large surface area of films and their small thickness make it possible to accelerate thermal, diffusive, and chemical processes at the gas-liquid boundary.Theoretical studies of liquid flow in a vertical descending thin layer are presented in [1–4]. In this paper we study ascending wave flows of a liquid in a thin vertical layer in contact with a gas, i.e., flows in the direction opposite the action of the force due to gravity, with account for the action of the gas on the liquid surface. Such motions are encountered when oil is extracted from strata that are saturated with gas. At some distance from the stratum the oil and gas separate: the gas travels at high velocity inside the pipe, occupying a considerable portion of the pipe, and the liquid is displaced toward the pipe walls, forming a thin film. In certain cases a wave-like interface develops between the oil and gas that travels with a velocity greater than that of the liquid but less than the average gas velocity. Similar phenomena are observed in high velocity mass exchangers.We examine the effect of the gas for both laminar and turbulent flow.Studies that neglect the effect of the gas flow on the liquid show that for waves on the film surface whose lengths are considerably longer than the average thickness of the layer, the liquid motion in the film is described by boundary layer equations in which account is taken of the mass force, i.e., the force due to gravity. With some approximation, we can assume that in accounting for the effect of the gas on the liquid the liquid flow is described by these same equations.     

Velocity distribution in horizontal slug flow

An experimental device for measurement of the velocity distribution in a two-phase slug is developed. Velocity profiles both in the film and the liquid slug besides velocity variation along the pipe bottom (at a distance of 1 mm) through the slug front are presented.     

Image correlation velocimetry applied to discrete smoke-wire streaklines in turbulent pipe flow

Two-colour image correlation velocimetry is applied to distinct smoke-wire streaklines in turbulent pipe flow. A single frame from a 35-mm film camera is exposed to two consecutive flashes, one from a red and one from a blue stroboscope. The resulting composite image is digitized, and the color components are extracted to obtain two images. Image correlation is then applied to estimate the velocity which is then compared with hot-wire velocity measurements.     

Numerical study of a piston-driven unsteady flow in a pipe with sudden expansion

This paper presents results of the numerical study of a piston-driven unsteady flow in a pipe with sudden expansion. The piston closes the larger-diameter pipe and moves between two limiting positions with strong acceleration or deceleration at the beginning and end of each stroke and constant velocity in between. The piston velocity in the exhaust stroke is about four times higher than in the intake stroke. Periodic piston movement in this fashion creates a complex unsteady flow between the piston head and the plane of sudden expansion. The numerical method is implicit and of finite volume type, using a moving grid and a collocated arrangement of variables. Second-order spatial discretization, fine grids and a multigrid solution method were used to ensure high accuracy and good efficiency. Spatial and temporal discretization errors were of the order of 1% and 0.1% respectively. The features of the flow are discussed and the velocity profiles are compared with experimental data, showing good qualitative and quantitative agreement.     

An oscillating hot-wire technique for resolving the magnitude and direction of velocity measurements using single hot-wire sensors

Thermal anemometry is a classic flow-velocity measurement technique that is known to suffer from the inability to discern the flow direction. The current paper describes an innovative approach whereby an oscillating hot wire is used to extract velocity direction and magnitude information from single hot-wire measurements. It is shown that the new sensor operates in one of two modes depending on the velocity amplitude of the wire oscillation. Furthermore, results from applying the technique to measure the phase-averaged velocity in an oscillating pipe flow experiment are presented. The results from the hot-wire measurements show good agreement with those from laser Doppler velocimetery measurements in the same facility.     

Reduction of beam refraction in optical pipe flow experiments by use of sheet-fabricated pipe walls

A measurement section is presented that allows for the study of liquid flows in straight pipes with noninvasive optical techniques. The amount of refraction of light rays is minimized by the use of short pipe sections manufactured of transparent film. For the situation of water, it is shown that walls as thin as 85?μm can be used in turbulent flows at high velocities. In our specific case, a flow of water at Reynolds numbers upto Re _D =300?000 in a pipe of Ø 70?mm diameter (average velocity 4?m/s) was realized without unacceptable vibrations of the pipe wall. In this situation laser Doppler measurements can be carried out without the need to correct for the position of the measurement volume or changes in the velocity response of the system.     

The characteristics of spiral waves in an axially rotating pipe

An experimental study of the instability of a flow in an axially rotating pipe is performed by means of LDV and flow visualization technique. It is found that the axial velocity of the rotating pipe flow fluctuates like a sine wave at first, then its fluctuating pattern assumes a somewhat sawtooth wave form as a spiral wave appears, which is predicted by means of linear and nonlinear stability analysis. At a certain rotation rate, the amplitude of the velocity fluctuations amounts to 30% of the axial velocity. At the down-stream section, another fluctuating component appears in the velocity, which interferes with the initially appearing component, then the fluctuation becomes one with broad-band spectral components. There is a close analogy between this spectral evolution and that of a Taylor-Couette flow. Deformation of the velocity distribution is obtained from the velocity fluctuating pattern and its phase, and the structure of the spiral wave is considered. The strength, azimuthal wavenumber and angular velocity of the spiral wave obtained from the velocity data are confirmed by flow visualization. The change of pressure loss in the rotating pipe is compared with the case without rotation.     

Laminar flow in the entrance region of a pipe

Summary The laminar flow of an incompressible fluid in the inlet of a pipe is analyzed numerically. The numerical technique allows a closer approximation to the basic equations of fluid motion than has been possible in previous investigations. Significant differences are shown between the results of the numerical solution and previous work for both velocity profiles and development lengths.     

Liquid film characterization in horizontal,annular, two-phase,gas–liquid flow using time-resolved laser-induced fluorescence

A non-intrusive optical technique was developed to provide time-resolved longitudinal and cross-sectional images of the liquid film in horizontal annular pipe flow of air and water, revealing the interfacial wave behavior. Quantitative information on the liquid film dynamics was extracted from the time-resolved images. The planar laser-induced fluorescence technique was utilized to allow for optical separation of the light emitted by the film from that scattered by the air–water interface. The visualization test section was fabricated from a tube presenting nearly the same refractive index as water, which allowed the visualization of the liquid film at regions very close to the pipe wall. Longitudinal images of the liquid film were captured using a high-frame-rate digital video camera synchronized with a high-repetition-rate laser. An image processing algorithm was developed to automatically detect the position of the air–water interface in each image frame. The thickness of the liquid film was measured at two axial stations in each processed image frame, providing time history records of the film thickness at two different positions. Wave frequency information was obtained by analyzing the time-dependent signals of film thickness for each of the two axial positions recorded. Wave velocities were measured by cross-correlating the amplitude signals from the two axial positions. For the film cross-section observations, two high-speed digital video cameras were used in a stereoscopic arrangement. Comparisons with results from different techniques available in literature indicate that the technique developed presents equivalent accuracy in measuring the liquid film properties. Time-resolved images of longitudinal and cross-section views of the film were recorded, which constitute valuable information provided by the technique implemented.     

Development of a thixotropic fluid flow in a pipe

This paper deals with the interaction between the modifications of the internal structure of a thixotropic fluid and the flow development along a pipe. The experimental set-up consists of a pipe, where a flow of thixotropic fluid is provided from a large vessel. The axial velocity distribution was determined using particle image velocimetry technique and ultrasonic velocity profile monitor. At the entrance section, the fluid is assumed to be in a homogeneous structural state corresponding to a high shear rate. The experimental results show a progressive flatness of the velocity profiles due to the aggregation of the structural elements of the fluid. The flow evolution is governed essentially by the kinetics of aggregation and segregation since the associated time scales are longer than the relaxation time of the flow. Received: 23 November 2000/Accepted: 20 May 2001     

The effect of pipe diameter on the structure of gas/liquid flow in vertical pipes

Experimental work on two-phase vertical upward flow was carried out using a 19 mm internal diameter, 7 m long pipe and studying the time series of cross-sectional average void fractions and pressure gradient which were obtained simultaneously. With the aid of a bank of published data in which the pipe diameter is the range from 0.5 to 70 mm, the effect of pipe diameter on flow characteristics of two-phase flow is investigated from various aspects. Particularly, the work focuses on the periodic structures of two-phase flow. Average film thicknesses and the gas flow rate where slug/churn and churn/annular flow transitions occur all increase as the diameter of the pipe becomes larger. On the other hand, the pressure gradients, the frequencies of the periodic structures and the velocities of disturbance waves decrease. The velocity of disturbance waves has been used to test the model of Pearce (1979). It is found that the suggested value of Pearce coefficient 0.8 is reasonable for lower liquid flow rates but becomes insufficient for higher liquid flow rates.     

Velocity profiles in shear force driven wall films

A wind tunnel experiment was carried out to investigate the structure, thickness and velocity profiles of a shear force driven liquid film. The local, time resolved film thickness was measured by means of a fluorescence technique, and a dedicated LDA system enabled the measurement of velocity profiles inside the thin and wavy film. The application of both techniques is briefly described.     

An analytical solution to non-axisymmetric heat transfer with viscous dissipation for non-Newtonian fluids in laminar forced flow

Forced convection heat transfer in a non-Newtonian fluid flow inside a pipe whose external surface is subjected to non-axisymmetric heat loads is investigated analytically. Fully developed laminar velocity distributions obtained by a power-law fluid rheology model are used, and viscous dissipation is taken into account. The effect of axial heat conduction is considered negligible. The physical properties are assumed to be constant. We consider that the smooth change in the velocity distribution inside the pipe is piecewise constant. The theoretical analysis of the heat transfer is performed by using an integral transform technique – Vodicka’s method. An important feature of this approach is that it permits an arbitrary distribution of the surrounding medium temperature and an arbitrary velocity distribution of the fluid. This technique is verified by a comparison with the existing results. The effects of the Brinkman number and rheological properties on the distribution of the local Nusselt number are shown.     

Turbulence modification in vertical upward annular flow passing through a throat section

Experimental studies on the turbulence modification in annular two-phase flow passing through a throat section were carried out. The turbulence modification in multi-phase flow due to the interactions between two-phases is one of the most interesting scientific issues and has attracted research attention. In this study, the gas-phase turbulence modification in annular flow due to the gas–liquid phase interaction is experimentally investigated. The annular flow passing through a throat section is under the transient state due to the changing cross sectional area of the channel and resultantly the superficial velocities of both phases are changed compared with a fully developed flow in a straight pipe. The measurements for the gas-phase turbulence were precisely performed by using a constant temperature hot-wire anemometer, and made clear the turbulence structure such as velocity profiles, fluctuation velocity profiles. The behavior of the interfacial waves in the liquid film flow such as the ripple or disturbance waves was also observed. The measurements for the liquid film thickness by the electrode needle method were also performed to measure the base film thickness, mean film thickness, maximum film thickness and wave height of the ripple or the disturbance waves.     

Evolution of jets effusing from inclined holes into crossflow

The turbulent flow structure and vortex dynamics of a jet-in-a-crossflow (JICF) problem, which is related to gas turbine blade film cooling, is investigated using the particle-image velocimetry (PIV) technique. A cooling jet emanating from a pipe interacts with a turbulent flat plate boundary layer at a Reynolds number Re_∞ = 400,000. The streamwise inclination of the coolant jet is 30° and two velocity ratios (VR = 0.28, VR = 0.48) and two mass flux ratios (MR = 0.28, MR = 0.48) are considered. Jets of air and CO₂ are injected separately into a boundary layer to examine the effects of the density ratio between coolant and mainstream on the mixing behavior and consequently, the cooling efficiency. The results show a higher mass flux ratio to enlarge the size of the recirculation region leading to a more pronounced entrainment of hot outer fluid into the wake of the jet. Furthermore, the lateral spreading of the coolant is strongly increased at a higher density ratio. The results of the experimental measurements are used to validate numerical findings. This comparison shows an excellent agreement for mean velocity and higher moment velocity distributions.     

输气管道壁面涂料减阻机理的实验研究

用IFA-300热线风速仪以高于对应最小湍流时间尺度的分辨率精细测量了风洞中不同壁面涂料的管道湍流边界层不同法向位置流向速度分量的时间序列信号,利用湍流边界层近壁区域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,在准确测量湍流边界层近壁区域对数律平均速度剖面的基础上,间接测量湍流边界层的壁面摩擦阻力．对不同壁面涂料的壁湍流脉动速度信号用子波分析进行多尺度分解,用子波系数的瞬时强度因子和平坦因子检测管道湍流边界层中的多尺度相干结构,提取不同尺度相干结构的条件相位平均波形,对比研究输气管道壁面涂料的减阻机理．     

Slip velocity measurements in an upward bubbly flow by combined LDA and electrodiffusional techniques

 An experimental technique for the measurement of the local slip velocity of spherical bubbles is reported. It is based on the measurement of the local liquid velocity by an electrodiffusional method, and the bubble velocity by a specially adapted LDA (Laser Doppler anemometer) with a short measuring volume. The bubble velocity is measured taking into account the shift between the bubble centre and the centre of the LDA measuring volume. The slip velocity is obtained by subtracting the liquid velocity from the bubble velocity at the point corresponding to the bubble centre. The technique is applicable for flows with high velocity gradients. Results of the slip velocity measurements in an upward bubbly flow at laminar pipe Reynolds numbers are presented. Received: 25 July 1996/Accepted: 13 April 1998