共查询到20条相似文献,搜索用时 747 毫秒
1.
When a polymeric melt flows through a contraction die, it experiences a certain distance in the slit before a fully developed flow is achieved, which is defined as the entrance length. Here, an equation for calculation of the entrance length was proposed based on an assumption that the pressure drops in an exponential function way along the flow direction in the contraction die from the entrance to the fully developed flow. The entrance length could be calculated from the flow parameters, such as volumetric flow rate, the pressures at the entrance and at the defined point in the fully developed flow. The entrance lengths of a low-density polyethylene (LDPE) and a high-density polyethylene (HDPE) melt were calculated from this equation with the measured flow parameters at various flow rates. The results are quite close to those measured from flow induced birefringence and similar to that reported in a published study by Martyn et al., which suggested that the equation could be used to describe the relation between the entrance length and the flow parameters. 相似文献
2.
A bow shock is observed in a two-dimensional supersonic flow of charged microparticles in a complex plasma. A thin conducting needle is used to make a potential barrier as an obstacle for the particle flow in the complex plasma. The flow is generated and the flow velocity is controlled by changing a tilt angle of the device under the gravitational force. A void, microparticle-free region, is formed around the potential barrier surrounding the obstacle. The flow is bent around the leading edge of the void and forms an arcuate structure when the flow is supersonic. The structure is characterized by the bow shock as confirmed by a polytropic hydrodynamic theory as well as numerical simulation. 相似文献
3.
We report an experimental study of flow dynamics and structure in turbulent thermal convection. Flow visualization, together with particle image velocimetry (PIV) measurement, reveal that the instantaneous flow structure consists of an elliptical circulatory roll and two smaller counterrotating rolls, and that the azimuthal motion of the quasi-2D instantaneous flow structure produces a time-averaged 3D flow pattern featuring two toroidal rings near the top and bottom plates, respectively. The apparently stochastic azimuthal motion of the flow structure, which generates a net rotation on average, is found to possess the characters of a Brownian ratchet. Using an artificially generated flow mode, we are able to produce a bimodal-Nu behavior and thus demonstrate that different flow states can indeed produce different global heat transport in a turbulent convection system. 相似文献
4.
The interaction between the flow field and the sound field is responsible for the sound absorption at perforated acoustic liners with bias flow and has to be investigated contactlessly. Based on the optically measured flow velocity spectrum, an energy analysis was performed. As a result, the generation of broadband flow velocity fluctuations in the shear layer surrounding the bias flow caused by the flow sound interaction has been observed. In addition, the magnitude of this acoustically induced flow velocity oscillation exhibits a correlation with the acoustic dissipation coefficient of the bias flow liner. This supports the assumption that an energy transfer between the flow field and the sound field is responsible for the acoustic damping. 相似文献
5.
Cho H Ren XH Sigmund EE Song YQ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,186(1):11-16
In this article, we demonstrate a single-scan method to measure an average flow velocity vector along an arbitrary direction. This method is based on the MMME sequence and utilizes static and pulsed magnetic field gradients along multiple directions for the optimal determination of flow velocity components in three-dimensional space. Experimentally measured average flow velocities from the flow induced phase shift with a single-scan MMME sequence show excellent agreements with the known flow rate, and the signal decay of each echo due to a velocity distribution is also quantitatively verified with known laminar flow patterns. 相似文献
6.
A computational and experimental approach is undertaken to study the enhancement of convective heat transfer in fully-developed internal flows by an electrically-induced secondary flow field. Using longitudinal flat electrodes along a parallel-plate configuration, the corona discharge is employed to generate an electrically induced secondary flow on the cross section of the flow passage. The electrically-induced secondary flow forms a swirling flow field in the fully-developed condition and enhances the heat transfer significantly. The flow field was solved computationally and the results were verified and validated by grid refinement study and computational error analysis. 相似文献
7.
Naomichi Yokoi Junki Sato Yuichi Shimatani Masaki Kyoso Hideki Funamizu Yoshihisa Aizu 《Optical Review》2014,21(3):345-352
In imaging of blood flow by means of a laser speckle technique, we have proposed so far an estimation parameter based on the spatial contrast of speckle patterns observed for the blood flow in skin tissue and a blood vessel. This parameter enable us to image a relative blood flow distribution from a single speckle pattern, thus, it analyzes the blood flow with a frame-rate of an imaging device used. In this study, we investigated availability of this parameter for detecting changes in arterial blood flow caused by medication and cold stimulation to the skin tissue. Experiments were conducted for an anesthetized rat and a human wrist to confirm the feasibility of the present parameter. 相似文献
8.
In order to observe and estimate the flow of fluid in three-dimensional space, the pulsed Doppler method has been used widely.
However, the velocity information acquired is only the velocity component in the beam direction of the wave even if an observation
plane is formed by beam scanning. Accordingly, it is difficult to know the velocity distribution in the observation plane
in tree-dimensional flow. In this paper, the new idea for processing the velocity distribution in the beam direction on an
observation plane for transposing to flux distribution (flow function method) has been introduced. Further, the flow in an
observation domain is divided into two kinds of flows, viz., the base flow which indicates the directivity of the flow in
the observation domain and the vortex which is considered a two-dimensional flow. By applying the theory of a stream function
to the two-dimensional flow, and by using the physical feature of a streamline to the base flow, the velocity component v
which intersects perpendicularly to the beam direction is estimated. The flow velocity distribution in a scanning plane (observation
plane) can be known from these two components of velocity, viz., beam direction componentu and perpendicular component to the beam directionv. The principle was explained by an example of the blood flow measurement in normal and abnormal heart chamber, by the ultrasonic
Doppler method. 相似文献
9.
The sound generation by an air flow in a corrugated tube is studied experimentally for different values of the corrugation pitch and different tube lengths. The Strouhal numbers of sound generated in different tubes with different flow velocities lie within 0.4–0.6. As the flow velocity increases, the Strouhal number decreases. The effect of sound absorption by an air flow in a corrugated duct is described: in a corrugated tube with a flow, at frequencies below the generation frequency, the absorption of sound produced by an external source is observed. A semiempirical model of aeroacoustic interaction in a corrugated tube is proposed. The model provides a qualitative agreement with the experiment. 相似文献
10.
Inspired by a mechanism of biological vision systems, a model and a network of analog metal oxide semiconductor (MOS) circuits are proposed which display an optical flow with local adaptation to the relative velocity of a background image. A function of displaying an optical flow successfully worked as a result of simulations using the simulation program with integrated circuit emphasis (SPICE). A function of varying an optical flow at a certain instant by local adaptation was also demonstrated. The proposed network is suitable for the realization of a large-scale integrated circuit (LSI), which displays an optical flow with local adaptation to the local velocity of a background. 相似文献
11.
Non-intrusive two-phase fluid pumping based on an electrohydrodynamically (EHD) induced flow phenomenon with free liquid surface
exposed to gas-phase corona discharges is experimentally investigated. Dielectric liquid flow generated near a corona discharge
electrode progresses toward an inclined plate electrode, and then climbs up the surface against the gravitational force for
an air-wave (AW) type EHD pump. The AW type EHD pump is operated on ionic wind field along the inclined plate electrode. The
pumping performance of time-averaged liquid flow rate and the liquid-phase flow motion are characterized. The liquid flow
characteristics related to a dimensionless parameter of corona discharge fields are presented. 相似文献
12.
M. Buffoni S. Camarri A. Iollo E. Lombardi M.V. Salvetti 《Journal of computational physics》2008,227(4):2626-2643
A method is proposed to estimate the velocity field of an unsteady flow using a limited number of flow measurements. The method is based on a non-linear low-dimensional model of the flow and on an expansion of the velocity field in terms of empirical basis functions. The main idea is to impose that the coefficients of the modal expansion of the velocity field gives the best approximation of the available measurements, while at the same time satisfying the non-linear low-order model as closely as possible. Practical applications may range from feedback flow control to the monitoring of the flow in non-accessible regions. The proposed technique is applied to the flow around a confined square cylinder, both in two- and three-dimensional flow regimes. Comparisons are provided with existing linear and non-linear estimation techniques. 相似文献
13.
14.
A Lattice Boltzmann method was employed to simulate active boundary layer flow control by means of a low-temperature surface
plasma. Plasma was generated by an AC input voltage over a surface electrode and an embedded electrode, resulting in an uneven
distribution of charges and an induced flow near the vicinity of the surface. Simulations were performed to examine the effect
of various geometrical parameters on the velocity flow profile and maximum velocity. 相似文献
15.
Unconfined granular flows along an inclined plane are investigated experimentally. During a long transient, the flow gets confined by quasistatic banks but still spreads laterally towards a well-defined asymptotic state following a nontrivial process. Far enough from the banks a scaling for the depth averaged velocity is obtained, which extends the one obtained for homogeneous steady flows. Close to jamming it exhibits a crossover towards a nonlocal rheology. We show that the levees, commonly observed along the sides of the deposit upon interruption of the flow, disappear for long flow durations. We demonstrate that the morphology of the deposit builds up during the flow, in the form of an underlying static layer, which can be deduced from surface velocity profiles, by imposing the same flow rule everywhere in the flow. 相似文献
16.
In Spring 2003, a new experimental course on flow visualization was offered to a mixed class of Fine Arts Photography and Engineering students. Course content included fluid flow physics, history of photography with respect to the relationship of science and art, as well as flow visualization and photography techniques. Issues such as “What makes an image art? What makes an image scientific?” were addressed. The class focused on studio/laboratory experiences for mixed teams of students. In Spring 2004 these concepts were distilled into an engineering outreach experience for middle school girls. The spectacular images resulting from these experiments show that flow visualization can be both performed and appreciated by a broad spectrum of people. Thus flow visualization may represent a new bridge between scientists and non-scientists. 相似文献
17.
This article presents the experimental results of an evaluation of the influence of internal flow patterns on the heat transfer performance of a closed-loop oscillating heat pipe with check valves. It was found that the internal flow patterns could be classified according to four flow patterns: dispersed bubble flow, bubble flow, slug flow, and annular flow, respectively. The main regime of each flow pattern can be determined from a flow pattern map. The map can be used to predict the trend of the heat transfer rate in the closed-loop oscillating heat pipe with check valves. 相似文献
18.
Understanding the physical features of the flow noise for an axisymmetric body is important for improving the performance of a sonar mounted on an underwater platform. Analytical calculation and numerical analysis of the physical features of the flow noise for an axisymmetric body are presented and a simulation scheme for the noise correlation on the hydrophones is given. It is shown that the numerical values of the flow noise coincide well with the analytical values. The main physical features of flow noise are obtained. The flow noises of two different models are compared and a model with a rather optimal fore-body shape is given. The flow noise in horizontal symmetry profile of the axisymmetric body is non-uniform, but it is omni-directional and has little difference in the cross section of the body. The loss of noise diffraction has a great effect on the flow noise from boundary layer transition. Meanwhile, based on the simulation, the noise power level increases with velocity to approximately the fifth power at high frequencies, which is consistent with the experiment data reported in the literature. Furthermore, the flow noise received by the acoustic array has lower correlation at a designed central frequency, which is important for sonar system design. 相似文献
19.
基于滑速比的气水两相流气相流量计算方法研究 总被引:1,自引:0,他引:1
目前对气水两相流的分相流量的研究中,多是针对两相流总流量和液相分相流量进行,对气相分相流量的研究很少.本文利用文丘里管和含气率传感器对空气水两相流气相流量计算方法进行了研究,在均相流模型基础上考虑了滑速比因素造成的影响,探讨了两相流气相流量计算方法.结果表明,该方法相对于传统的均相流模型在计算精度上得到了显著提高. 相似文献