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1.
To develop a quantitative understanding of unsteady and interacting turbomachine flow fields, it is necessary to quantify
the instantaneous efficiency of high speed turbomachines. This requires the measurement of both the unsteady velocity and
total temperature variation in the exit flow of a high speed rotor. In this paper, techniques to utilize a single slant-film
anemometer to measure unsteady total temperature are developed and evaluated. Then a series of preliminary experiments are
performed in a high speed axial fan facility to quantify the instantaneous rotor efficiency. This is accomplished by utilizing
these single slant-film methods to measure the total temperature in the rotor wakes. Results show that measurements at multiple
overheats and several probe orientations are required. The simplest method proves to be useful for determining parameters
used in other methods. An analysis based on King’s law gives good results even when measurements are outside the calibration
range. Within the calibration range, a polynomial representation of the wire response to mass flux and total temperature yields
good total temperature fluctuation results. A model analysis technique is also assessed.
Received: 13 November 1997/Accepted: 16 February 1998 相似文献
2.
This study concentrates on the unsteady magnetohydrodynamics (MHD) rotating flow of an incompressible generalized Burgers’s
fluid past a suddenly moved plate through a porous medium. Modified Darcy’s law for generalized Burgers’s fluid in a rotating
frame has been used to model the governing flow problem. The closed form solution of the governing flow problem has been obtained
by employing Laplace transform technique. The integral appearing in the inverse Laplace transform has been evaluated numerically.
The influence of various parameters on the velocity profile has been delineated through several graphs and discussed in detail.
It was found that the fluid is decelerated with increasing Hartmann number M and porosity parameter K. However, for large Hall parameter m, the real part of velocity decreases and the imaginary part of velocity increases. 相似文献
3.
In wall-bounded turbulent flows, determination of wall shear stress is an important task. The main objective of the present
work is to develop a sensor which is capable of measuring surface shear stress over an extended region applicable to wall-bounded
turbulent flows. This sensor, as a direct method for measuring wall shear stress, consists of mounting a thin flexible film
on the solid surface. The sensor is made of a homogeneous, isotropic, and incompressible material. The geometry and mechanical
properties of the film are measured, and particles with the nominal size of 11 μm in diameter are embedded on the film’s surface
to act as markers. An optical technique is used to measure the film deformation caused by the flow. The film has typically
deflection of less than 2% of the material thickness under maximum loading. The sensor sensitivity can be adjusted by changing
the thickness of the layer or the shear modulus of the film’s material. The paper reports the sensor fabrication, static and
dynamic calibration procedure, and its application to a fully developed turbulent channel flow at Reynolds numbers in the
range of 90,000–130,000 based on the bulk velocity and channel full height. The results are compared to alternative wall shear
stress measurement methods. 相似文献
4.
Precise flow rate measurements of natural gas under high pressure with a laser Doppler velocity profile sensor 总被引:1,自引:0,他引:1
L. Büttner C. Bayer A. Voigt J. Czarske H. Müller N. Pape V. Strunck 《Experiments in fluids》2008,45(6):1103-1115
This paper reports about the first application of a laser Doppler velocity profile sensor for precise flow rate measurements
of natural gas under high pressure. The profile sensor overcomes the limitations of conventional laser Doppler anemometry
(LDA) namely the effect of spatial averaging and the effect of fringe spacing variation (virtual turbulence). It uses two
superposed, fan-like interference fringe systems to determine the axial position of a tracer particle inside the LDA’s measurement
volume. Consequently, a spatial resolution of about 1 μm can be achieved and the effect of virtual turbulence is nearly eliminated.
These features predestine the profile sensor for flow rate measurements with high precision. Velocity profile measurements
were performed at the German national standard for natural gas, one of the world′s leading test facilities for precision flow
rate measurements. As a result, the velocity profile of the nozzle flow could be resolved more precisely than with a conventional
LDA. Moreover, the measured turbulence intensity of the core flow was of 0.14% mean value and 0.07% minimum value, which is
significantly lower than reference measurements with a conventional LDA. The paper describes the performed measurements, gives
a discussion and shows possibilities for improvements. As the main result, the goal of 0.1% flow rate uncertainty seems possible
by an application of the profile sensor. 相似文献
5.
We studied numerically the heat transfer for a turbulent flow of supercritical helium. A finite difference model is constructed
with three different models of turbulence: the mixing length,k- andk-ε model. The stationary results compared to experimental data reveal that the mixing length model gives the best prediction
of turbulence in this situation. A severe deterioration from the widely used Nusselt correlation by Giarratano is observed
for cases near the pseudocritical temperature, while a far better correspondance is found with the more recent Yaskin correlation.
The maxima and minima in the heat transfer curves can be understood by interpretation of the wall and bulk temperature together
with the strong changes in density. 相似文献
6.
A steady-state plane channel flow of viscous incompressible fluid with no-slip and heat transfer boundary conditions is considered.
The flow is induced by a fixed pressure difference and the fluid viscosity depends on the temperature in accordance with a
power law. It is shown numerically that the dependence of the Peclet number on the nondimensional pressure difference is not
single-valued. An investigation of the solution’s dependence on the Biot number shows that for Biot numbers greater than unity
the velocity profile has a point of inflection.
Perm’. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 75–80, March–April, 2000.
The work received financial support from the Russian Foundation for Basic Research (project N97-01-00063). 相似文献
7.
An empirical correlation for the onset of turbulence in physiological pulsatile flow is presented. We pumped three different
test fluids of kinematic viscosity 0.008–0.035 cm2/s through four straight tubes 0.4–3.0 cm in diameter. A Scotch yoke mechanism provided an oscillatory sine wave flow component
of known stroke volume and frequency. We adjusted the mean flow independently until we detected signal instabilities from
hot film wall shear stress probes.
The critical peak Reynolds number was found to correlate with the Womersley parameter and the Strouhal number as a power law
function with a root-mean-square (rms) error of 15.2%. Experimental measurements of the laminar velocity profile are compared
to theoretical predictions from Poiseuille’s law and Womersley’s solution.
Received: 30 October 1995/Accepted: 7 April 1997 相似文献
8.
Fluid flow at the interface of a porous medium and an open channel is the governing phenomenon in a number of processes of
industrial importance. Traditionally, this has been modeled by applying the Brinkman’s modification of Darcy’s law to obtain
the velocity profile in terms of an additional parameter known as the “apparent viscosity” or the “slip coefficient”. To test
this ad hoc approach, a detailed experimental investigation of the flow was conducted using Laser Doppler Anemometry (LDA) in the close
vicinity of the permeable boundary of a porous medium. The porous medium used in the experiments consisted of a network of
continuous glass strands woven together in a random fashion.
A Hele–Shaw cell was partially filled with a fibrous preform such that an open channel flow is coupled with the Darcy flow
inside the preform through the permeable interface of the preform. The open channel portion of the Hele–Shaw cell also acts
as an ideal porous medium of known in-plane permeability which is much higher than the permeability of the fibrous porous
medium. A viscous fluid is injected at a constant flow rate through the above arrangement and a saturated and steady flow
is established through the cell. Using LDA, steady state velocity profiles are accurately measured by traversing across the
cell in the direction perpendicular to the flow. A series of experiments were conducted in which fluid viscosity, flow rate,
solid volume fraction of the porous medium and depth of the Hele–Shaw cell were varied. For each and every case in which the
conditions for Hele–Shaw approximation were valid, the depth of the boundary layer zone or the screening length inside the
fibrous preform was found to be of the order of the channel depth. This is much larger as compared to the Brinkman’s prediction
of the screening length which is of the order of √K, where K is the permeability of the fibrous porous medium. Based on this finding, we modified the boundary condition in the Brinkman’s
solution and found that the velocity profile results compared well with the experimental data for the planar geometry and
the fibrous preforms for volume fractions of 7%, 14% and 21% for Hele–Shaw cell depths of 1.6 and 3.175 mm. For a cell depth
of 4.8 cm, in which the Hele–Shaw approximation was not valid, the boundary layer thickness or the screening length was found
to be less than the mold or channel depth but was still much larger than the Brinkman’s prediction.
Received: 10 May 1996 / Accepted: 26 August 1996 相似文献
9.
A spatially self-referencing velocimetry system based on low-coherence interferometry has been developed. The measurement
technique is contactless and relies on the interference between back-reflected light from an arbitrary reference surface and
seeding particles in the flow. The measurement location and the flow velocity are measured relative to the reference surface’s
location and velocity, respectively. Scanning of the measurement location along the beam direction does not require mechanical
movement of the sensor head. The reference surface (which can move or vibrate relative to the sensor head) can be either an
external object or the surface of a body over which measurements are to be performed. The absolute spatial accuracy and the
spatial resolution only depend on the coherence length of the light source (tens of microns for a superluminescent diode).
The prototype is an all-fiber assembly. An optical fiber of arbitrary length connects the self-contained optical and electronics
setup to the sensor head. Proof-of-principle measurements in water (Taylor–Couette flow) and in air (Blasius boundary layer)
are reported in this paper. 相似文献
10.
A generalized mass transfer law unifying various particle transport mechanisms in dilute dispersions
Abhijit Guha 《Heat and Mass Transfer》2008,44(11):1289-1303
A generalized mass transfer law for dilute dispersion of particles (or droplets) of any sizes suspended in a fluid has been
described, which can be applied to turbulent or laminar flow. The generalized law reduces to the Fick’s law of diffusion in
the limit of very small particles. Thus the study shows how the well-known and much-used Fick’s law of diffusion fits into
the broader context of particle transport. The general expression for particle flux comprises a diffusive flux due to Brownian
motion and turbulent fluctuation, a diffusive flux due to temperature gradient (thermophoresis plus stressphoresis) and a
convective flux that arises primarily due to the interaction of particle inertia and the inhomogeneity of the fluid turbulence
field (turbophoresis). Shear-induced lift force, electrical force, gravity, etc. also contribute to the convective flux. The
present study includes the effects of surface roughness, and the calculations show that the presence of small surface roughness
even in the hydraulically smooth regime significantly enhances deposition especially of small particles. Thermophoresis can
have equally strong effects, even with a modest temperature difference between the wall and the bulk fluid. For particles
of the intermediate size range, turbophoresis, thermophoresis and roughness are all important contributors to the overall
deposition rate. The paper includes a parametric study of the effects of electrostatic forces due to mirror charging. The
present work provides a unified framework to determine the combined effect of various particle transport mechanisms on mass
transfer rate and the inclusion of other mechanisms not considered in this paper is possible. 相似文献
11.
This paper generalizes the analysis of four magnetohydrodynamic (MHD) flow problems of an Oldroyd-B fluid discussed by Asghar
et al. [Int. J. Non-linear Mech. 40, 589–601 (2005)] into three directions: (i) to discuss the problems in a porous medium using modified Darcy’s law (ii) to
see the influence of Hall current (iii) to determine the effect of rheological parameter of Burgers’ fluid. Analytical solutions
of velocity distribution valid at large and small times are given in each problem. Comparison has been provided for Oldroyd-B
and Burgers’ fluids through graphs. The physical interpretation is also included. 相似文献
12.
M. I. Gritsevich 《Moscow University Mechanics Bulletin》2010,65(4):94-95
The general equation describing the motion of a meteoroid in the Earth’s atmosphere is considered. It is shown that, in this
case, the momentum variation of the system consisting of the meteoroid and its separating mass is due to the velocity variation
of the meteoroid. The projection of Newton’s equation onto the tangent to the meteoroid trajectory is analyzed. It is also
shown that, because of large geocentric velocities (between 11 and 72 km/s), the dominant force is the drag force proportional
to the square of the incident air flow velocity. Some numerical results obtained for the Bene>sov bolide registered by the
European Fireball Network (May 7, 1991) are given as an illustrative example. 相似文献
13.
In this study, the flow of a fourth order fluid in a porous half space is modeled. By using the modified Darcy’s law, the
flow over a suddenly moving flat plate is studied numerically. The influence of various parameters of interest on the velocity
profile is revealed.
The English text was polished by Keren Wang. 相似文献
14.
Numerical simulation of blood flow and interstitial fluid pressure in solid tumor microcirculation based on tumor-induced angiogenesis 总被引:1,自引:0,他引:1
Gaiping Zhao Jie Wu Shixiong Xu M. W. Collins Quan Long Carola S. König Yuping Jiang Jian Wang A. R. Padhani 《Acta Mechanica Sinica》2007,23(5):477-483
A coupled intravascular–transvascular–interstitial fluid flow model is developed to study the distributions of blood flow
and interstitial fluid pressure in solid tumor microcirculation based on a tumor-induced microvascular network. This is generated
from a 2D nine-point discrete mathematical model of tumor angiogenesis and contains two parent vessels. Blood flow through
the microvascular network and interstitial fluid flow in tumor tissues are performed by the extended Poiseuille’s law and
Darcy’s law, respectively, transvascular flow is described by Starling’s law; effects of the vascular permeability and the
interstitial hydraulic conductivity are also considered. The simulation results predict the heterogeneous blood supply, interstitial
hypertension and low convection on the inside of the tumor, which are consistent with physiological observed facts. These
results may provide beneficial information for anti-angiogenesis treatment of tumor and further clinical research.
The project supported by the National Natural Science Foundation of China (10372026). 相似文献
15.
The heat transfer model of laminar pulsating flow in a tube in rolling motion is established. The correlations of velocity,
temperature and Nusselt number are obtained. The effects of several parameters on Nusselt number are investigated. The theoretical
results are consistent with experimental data. Then the results are evaluated with Nield and Kuznetsov’s results. It is found
that Nield and Kuznetsov’s results are not applicable for the laminar pulsating flow in nuclear power systems in ocean environments. 相似文献
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18.
H. Oualli S. Hanchi A. Bouabdellah R. Askovic M. Gad-El-Hak 《Experiments in fluids》2008,44(5):807-818
The flow around a circular cylinder with a cross-section variation is experimentally investigated. Particle Image Velocimetry
(PIV) is used to scrutinize the interaction of the cylinder’s wall with its near wake. The Reynolds number based on the cylinder’s
diameter and freestream velocity is 80 × 103, corresponding to the upper subcritical flow regime. At a forcing Strouhal number of St
f = 0.02, the maximum vorticity level around the cylinder is reduced by more than 50% as compared to its uncontrolled value.
The topology of the bulk flow confined between the primary vortical structure and the cylinder surface is modified resulting
in substantial drag reduction. 相似文献
19.
In this paper steady flow of a third grade fluid through porous space is considered. Modified Darcy’s law for third grade
fluid in a porous space has been introduced. The governing non-linear equation is first modelled and then solved using homotopy
analysis method (HAM). The convergence of the obtained series solution is discussed. The effects of the emerging parameters
on the velocity field are seen. It is noted that meaningful solution exists only in the case of suction. 相似文献
20.
In a two-phase (liquid–gas) two-component (water–hydrogen) system we discuss the formulation of the possible dissolution of
hydrogen in the liquid phase. We show how Henry’s law fits in a phase diagram and the problem is formulated as a set of nonlinear
partial differential equations with complementarity constraints. 相似文献