The discharge plume parameter and its implications for an emptying–filling box

2017 ◽  
Vol 817 ◽  
pp. 171-182 ◽  
Author(s):  
O. Vauquelin ◽  
E. M. Koutaiba ◽  
E. Blanchard ◽  
P. Fromy
Keyword(s):  
Steady State ◽  
Natural Ventilation ◽  
Discharge Coefficient ◽  
Fluid Layer ◽  
Buoyant Plume ◽  
Layer Depth ◽  
Dimensional Parameter ◽  
Fluid Layers ◽  
Momentum Fluxes ◽  
Lower Opening

The natural ventilation flow driven by an internal buoyant plume in a box involving an upper opening (vent) located at the ceiling (for the outflow) and a large lower opening at the floor (for the inflow) is examined theoretically in a general non-Boussinesq case. Analytical solutions of this emptying–filling box problem allow the characteristics of the flow at the vent to be determined. From these characteristics, a non-dimensional parameter $\unicode[STIX]{x1D6E4}_{d}$ (called the discharge plume parameter) is expressed. This parameter characterizes the initial balance of volume, buoyancy and momentum fluxes in the plume-like flow that forms above the vent. We then note that the value of $\unicode[STIX]{x1D6E4}_{d}$ allows the buoyant fluid layer depth in the box to be estimated, which is a new and interesting result for natural ventilation problems. Following previous experimental results, the decrease of the vent discharge coefficient $C_{d}$ when $\unicode[STIX]{x1D6E4}_{d}$ increases is discussed and a theoretical model based on plume necking is proposed. The emptying–filling box model is then extended for a variable $C_{d}$ (depending on $\unicode[STIX]{x1D6E4}_{d}$). Even though the discharge coefficient may be markedly reduced at high values of $\unicode[STIX]{x1D6E4}_{d}$, our results show that this only affects transients and the steady state of an emptying–filling box for relatively thin buoyant fluid layers.

Plane turbulent jets in a bounded fluid layer

1992 ◽  
Vol 241 ◽  
pp. 587-614 ◽  
Author(s):  
T. Dracos ◽  
M. Giger ◽  
G. H. Jirka
Keyword(s):  
Experimental Investigation ◽  
Cross Section ◽  
Fluid Layer ◽  
Three Dimensional ◽  
Turbulent Jets ◽  
Two Dimensional ◽  
Vortical Structures ◽  
Secondary Currents ◽  
Fluid Layers ◽  
Bounding Surfaces

An experimental investigation of plane turbulent jets in bounded fluid layers is presented. The development of the jet is regular up to a distance from the orifice of approximately twice the depth of the fluid layer. From there on to a distance of about ten times the depth, the flow is dominated by secondary currents. The velocity distribution over a cross-section of the jet becomes three-dimensional and the jet undergoes a constriction in the midplane and a widening near the bounding surfaces. Beyond a distance of approximately ten times the depth of the bounded fluid layer the secondary currents disappear and the jet starts to meander around its centreplane. Large vortical structures develop with axes perpendicular to the bounding surfaces of the fluid layer. With increasing distance the size of these structures increases by pairing. These features of the jet are associated with the development of quasi two-dimensional turbulence. It is shown that the secondary currents and the meandering do not significantly affect the spreading of the jet. The quasi-two-dimensional turbulence, however, developing in the meandering jet, significantly influences the mixing of entrained fluid.

Super-Fine Structure in the Critical Flow-Rate of Critical Flow Venturi Nozzles

2002 ◽  
Author(s):  
Masahiro Ishibashi
Keyword(s):  
Fine Structure ◽  
Steady State ◽  
Discharge Coefficient ◽  
Constant Pressure ◽  
Pressure Ratio ◽  
Critical Flow ◽  
Time Intervals ◽  
Critical Flow Rate ◽  
A Value ◽  
Long Time

It is shown that critical flow Venturi nozzles need time intervals, i.e., more than five hours, to achieve steady state conditions. During these intervals, the discharge coefficient varies gradually to reach a value inherent to the pressure ratio applied. When a nozzle is suddenly put in the critical condition, its discharge coefficient is trapped at a certain value then afterwards approaches gradually to the inherent value. Primary calibrations are considered to have measured the trapped discharge coefficient, whereas nozzles in applications, where a constant pressure ratio is applied for a long time, have a discharge coefficient inherent to the pressure ratio; inherent and trapped coefficients can differ by 0.03–0.04%.

scholarly journals Indentation into a plastic fluid layer

2019 ◽  
Vol 475 (2224) ◽  
pp. 20180747
Author(s):  
Thomasina V. Ball ◽  
Neil J. Balmforth ◽  
Ian J. Hewitt
Keyword(s):  
Slip Line ◽  
Plastic Material ◽  
Fluid Layer ◽  
Viscoplastic Fluid ◽  
Parallel Plates ◽  
Viscoplastic Material ◽  
Layer Depth ◽  
Glass Spheres ◽  
Theoretical Predictions ◽  
Line Theory

We study the indentation of a rigid object into a layer of a cohesive or non-cohesive plastic material. Existing approaches to this problem using slip-line theory assume that the penetration depth is relatively small, employing perturbation theory about a flat surface. Here, we use two alternative approaches to account for large penetration depths, and for the consequent spreading and uplift of the surrounding material. For a viscoplastic fluid, which reduces to an ideal plastic under the limit of vanishing viscosity, we adopt a viscoplastic version of lubrication theory. For a Mohr–Coulomb material, we adopt an extension of slip-line theory between two parallel plates to account for arbitrary indenter shapes. We compare the theoretical predictions of penetration and spreading with experiments in which a flat plate, circular cylinder or sphere are indented into layers of Carbopol or glass spheres with successively higher loads. We find reasonable agreement between theory and experiment, though with some discrepancies that are discussed. There is a clear layer-depth dependence of the indentation and uplift for the viscoplastic material. For a cylinder indented into a Mohr–Coulomb material, there is a much weaker dependence on layer depth.

Throughflow effects on convective instability in superposed fluid and porous layers

1991 ◽  
Vol 231 ◽  
pp. 113-133 ◽  
Author(s):  
Falin Chen
Keyword(s):  
Porous Layer ◽  
Convective Instability ◽  
Fluid Layer ◽  
Critical Rayleigh Number ◽  
Vertical Direction ◽  
Single Layer ◽  
Layer Depth ◽  
Onset Of Convection ◽  
Precise Control ◽  
Porous Layers

We implement a linear stability analysis of the convective instability in superposed horizontal fluid and porous layers with throughflow in the vertical direction. It is found that in such a physical configuration both stabilizing and destabilizing factors due to vertical throughflow can be enhanced so that a more precise control of the buoyantly driven instability in either a fluid or a porous layer is possible. For ζ = 0.1 (ζ, the depth ratio, defined as the ratio of the fluid-layer depth to the porous-layer depth), the onset of convection occurs in both fluid and porous layers, the relation between the critical Rayleigh number Rcm and the throughflow strength γm is linear and the Prandtl-number (Prm) effect is insignificant. For ζ ≥ 0.2, the onset of convection is largely confined to the fluid layer, and the relation becomes Rcm ∼ γ2m for most of the cases considered except for Prm = 0.1 with large positive γm where the relation Rcm ∼ γ3m holds. The destabilizing mechanisms proposed by Nield (1987 a, b) due to throughflow are confirmed by the numerical results if considered from the viewpoint of the whole system. Nevertheless, from the viewpoint of each single layer, a different explanation can be obtained.

Thermal Instability of a Fluid-Saturated Porous Medium Bounded by Thin Fluid Layers

1987 ◽  
Vol 109 (3) ◽  
pp. 677-682 ◽  
Author(s):  
G. Pillatsis ◽  
M. E. Taslim ◽  
U. Narusawa
Keyword(s):  
Porous Medium ◽  
Porous Layer ◽  
Thermal Instability ◽  
Numerical Solutions ◽  
Fluid Layer ◽  
Critical Rayleigh Number ◽  
Convective Motion ◽  
Wave Number ◽  
Thermal Conductivity Ratio ◽  
Fluid Layers

A linear stability analysis is performed for a horizontal Darcy porous layer of depth 2dm sandwiched between two fluid layers of depth d (each) with the top and bottom boundaries being dynamically free and kept at fixed temperatures. The Beavers–Joseph condition is employed as one of the interfacial boundary conditions between the fluid and the porous layer. The critical Rayleigh number and the horizontal wave number for the onset of convective motion depend on the following four nondimensional parameters: dˆ ( = dm/d, the depth ratio), δ ( = K/dm with K being the permeability of the porous medium), α (the proportionality constant in the Beavers–Joseph condition), and k/km (the thermal conductivity ratio). In order to analyze the effect of these parameters on the stability condition, a set of numerical solutions is obtained in terms of a convergent series for the respective layers, for the case in which the thickness of the porous layer is much greater than that of the fluid layer. A comparison of this study with the previously obtained exact solution for the case of constant heat flux boundaries is made to illustrate quantitative effects of the interfacial and the top/bottom boundaries on the thermal instability of a combined system of porous and fluid layers.

Synthetic full‐waveform acoustic logs in cased boreholes, II—Poorly bonded casing

Geophysics ◽  
1986 ◽  
Vol 51 (4) ◽  
pp. 902-913 ◽  
Author(s):  
Kenneth M. Tubman ◽  
C. H. Cheng ◽  
S. P. Cole ◽  
M. Nafi Toksöz
Keyword(s):  
Wave Propagation ◽  
Elastic Wave ◽  
Theoretical Study ◽  
Fluid Layer ◽  
Body Wave ◽  
P Wave ◽  
Full Waveform ◽  
Fluid Layers ◽  
First Arrival ◽  
Wave Arrival

A generalization of the technique of Tubman et al. (1984) allows the inclusion of intermediate fluid layers in the theoretical study of elastic wave propagation in a layered borehole. The number and location of fluid layers are arbitrary. The only restrictions are that the central cylinder is fluid and the outermost formation is solid. Synthetic full‐waveform microseismograms in poorly bonded cased holes can be generated, allowing investigation of free pipe and cement sheathed pipe with no bond to the formation. If there is a fluid layer between the steel and the cement, the steel is free to ring. The first arrival in this situation is from the casing, even with an extremely thin fluid layer or microannulus. The amplitude and duration of the pipe signal depend upon the thickness of the fluid layer. While the first arrival is from the casing, the formation body‐wave energy is present. The character of the waveform will vary as the formation parameters vary. If the duration of the steel arrival is small, it is possible to distinguish the formation P-wave arrival. If the fluid layer is between the cement and the formation, then the steel is well bonded to the cement but the cement is not bonded to the formation. In this case the thicknesses of the fluid and cement layers are important in determining the nature of the first arrival. If there is a large amount of cement bonded to the steel, the cement can damp out the ringing of the pipe and make it possible to distinguish formation arrivals. If there is less cement bonded to the steel, the cement does not damp out the steel ringing but the cement rings along with the steel and the first arrival is from the combination of the steel and the cement. The velocity of this wave depends upon the velocities and thicknesses of the steel and cement layers.

Thermal Stability of Two Fluid Layers Separated by a Solid Interlayer of Finite Thickness and Thermal Conductivity

1984 ◽  
Vol 106 (3) ◽  
pp. 605-612 ◽  
Author(s):  
I. Catton ◽  
J. H. Lienhard
Keyword(s):  
Thermal Conductivity ◽  
Fluid Layer ◽  
Heated Surface ◽  
Finite Thickness ◽  
Fluid Layers ◽  
The Stability ◽  
Stability Limits ◽  
Range Of Values ◽  
Two Fluid ◽  
Thermal Stability Of

Stability limits of two horizontal fluid layers separated by an interlayer of finite thermal conductivity are determined. The upper cooled surface and the lower heated surface are taken to be perfectly conducting. The stability limits are found to depend on the ratio of fluid layer thicknesses, the ratio of interlayer thickness to total fluid layer thickness, and the ratio of fluid thermal conductivity to interlayer thermal conductivity. Results are given for a range of values of each of the governing parameters.

In-Cylinder Flow Correlations Between Steady Flow Bench and Motored Engine Using Computational Fluid Dynamics

2017 ◽  
Vol 139 (7) ◽  
Author(s):  
Xiaofeng Yang ◽  
Tang-Wei Kuo ◽  
Orgun Guralp ◽  
Ronald O. Grover ◽  
Paul Najt
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Steady State ◽  
Velocity Profile ◽  
Discharge Coefficient ◽  
Intake Port ◽  
Charge Motion ◽  
Steady State Flow ◽  
Cfd Simulations ◽  
Motored Engine

Intake port flow performance plays a substantial role in determining the volumetric efficiency and in-cylinder charge motion of a spark-ignited engine. Steady-state flow bench and motored engine flow computational fluid dynamics (CFD) simulations were carried out to bridge these two approaches for the evaluation of port flow and charge motion (such as discharge coefficient, swirl/tumble ratios (SR/TR)). The intake port polar velocity profile and polar physical clearance profile were generated to evaluate the port performance based on local flow velocity and physical clearance in the valve-seat region. The measured data were taken from standard steady-state flow bench tests of an intake port for validation of CFD simulations. It was reconfirmed that the predicted discharge coefficients and swirl/tumble index (SI/TI) of steady flow bench simulations have a good correlation with those of motored engine flow simulations. Polar velocity profile is strongly affected by polar physical clearance profile. The polar velocity inhomogeneity factor (IHF) correlates well with the port discharge coefficient, swirl/tumble index. Useful information can be extracted from local polar physical clearance and velocity, which can help for intake port design.

Sign in / Sign up

Export Citation Format

Share Document