A Theoretical Model for Nonseparated Mixing of a Confined Jet

1972 ◽  
Vol 94 (3) ◽  
pp. 551-556 ◽  
Author(s):  
E. Razinsky ◽  
J. A. Brighton
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Flow Model ◽  
Flow Conditions ◽  
Low Velocity ◽  
Fully Developed Flow ◽  
Wall Boundary Layer ◽  
Flow Development ◽  
Constant Diameter ◽  
Entire Flow

A model and procedure for calculating turbulent mixing of a confined jet is presented. The flow consists of a high velocity jet which is directed into a constant diameter duct, where it mixes with a concentric, low velocity stream. The flow model which includes the wall boundary layer covers the entire flow development from the mixing tube entrance to the start of fully developed flow conditions. The calculated results are presented for a range of flow conditions and are compared with the experimental results of a previous paper by the same authors. It was found that including the boundary layer, as part of the model, gave results which were significantly different and in better agreement with experiment for small and moderate velocity ratios.

scholarly journals Heat Transfer and Fluid Dynamics Measurements in Accelerated Rough-Wall Boundary Layer

1993 ◽  
Author(s):  
Walid Chakroun ◽  
Robert P. Taylor
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Reynolds Shear Stress ◽  
Rough Wall ◽  
Rough Boundary ◽  
Flow Conditions ◽  
Wall Boundary Layer

The combined effects of freestream acceleration and surface roughness on heat transfer and fluid dynamics in the turbulent boundary layer were investigated experimentally. The experiments included a variety of flow conditions ranging from aerodynamically-smooth through transitionally-rough to fully-rough boundary layers with accelerations ranging from moderate to modestly strong. Two well-defined rough surfaces composed of 1.27 mm diameter hemispheres spaced 2 and 4 diameters apart, respectively, in staggered arrays on otherwise smooth surfaces were used as the test surfaces. The first 1.5 m of the test section had zero-pressure gradient followed by a 0.4 m accelerated region with the remaining 0.4 m adjusted to zero-pressure gradient. The Stanton number for the rough-wall experiments decreased or increased for accelerated rough-wall cases compared to zero-pressure gradient cases depending on flow conditions. For fully-rough boundary layers, Stanton numbers increased with acceleration compared to zero-pressure gradient at the same x-position. For aerodynamically-smooth and transitionally-rough boundary-layer flows, the effect of acceleration was not similar to that of fully-rough flows and was highly dependent upon the flow conditions. The acceleration caused a decrease in the relative turbulence level over the rough surface. The profiles of u′2¯ for the accelerated runs were lower than those of zero-pressure gradient cases, and a substantial decrease in the Reynolds shear stress (−u′v′¯) component was observed when acceleration was applied.

An Analysis on the Flow in a Casing Induced by a Rotating Disk Using a Four-Layer Flow Model

1976 ◽  
Vol 98 (2) ◽  
pp. 192-198 ◽  
Author(s):  
Y. Senoo ◽  
H. Hayami
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Analytical Study ◽  
Flow Model ◽  
Equations Of Motion ◽  
Side Wall ◽  
Rotating Disk ◽  
Wall Boundary Layer ◽  
Through Flow ◽  
Layer Flow

An analytical study has been made to clarify the details of the flow between a rotating disk and a stationary casing side-wall with and without an axisymmetric inward through-flow. The flow field between the casing side-wall and the surface of the rotating disk is divided into four layers instead of three in earlier analyses. Proceeding from the casing side-wall to the disk, they are a wall boundary layer, an outward-flow layer, a core and a disk boundary layer. The flow field is determined so that the integrated equations of motion as well as the continuity equation are satisfied for each of the four layers. In the present analysis, least empirical informations relative to a rotating disk are used compared with the theories in the literature. The mechanics of the flow field is explained by the flow model without contradiction, and the predicted radial and axial distributions of velocity and the pressure distribution in the casing agree well with experimental results.

scholarly journals Modeling microphysical effects of entrainment in clouds observed during EUCAARI-IMPACT field campaign

2013 ◽  
Vol 13 (16) ◽  
pp. 8489-8503 ◽  
Author(s):  
D. Jarecka ◽  
H. Pawlowska ◽  
W. W. Grabowski ◽  
A. A. Wyszogrodzki
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Marine Boundary Layer ◽  
Cloud Droplet ◽  
Droplet Radius ◽  
Subgrid Scale ◽  
Microphysics Scheme ◽  
Local Conditions ◽  
Field Campaign ◽  
Les Model

Abstract. This paper discusses aircraft observations and large-eddy simulation (LES) modeling of 15 May 2008, North Sea boundary-layer clouds from the EUCAARI-IMPACT field campaign. These clouds are advected from the northeast by the prevailing lower-tropospheric winds and featured stratocumulus-over-cumulus cloud formations. An almost-solid stratocumulus deck in the upper part of the relatively deep, weakly decoupled marine boundary layer overlays a field of small cumuli. The two cloud formations have distinct microphysical characteristics that are in general agreement with numerous past observations of strongly diluted shallow cumuli on one hand and solid marine stratocumulus on the other. Based on the available observations, a LES model setup is developed and applied in simulations using a novel LES model. The model features a double-moment warm-rain bulk microphysics scheme combined with a sophisticated subgrid-scale scheme allowing local prediction of the homogeneity of the subgrid-scale turbulent mixing. The homogeneity depends on the characteristic time scales for the droplet evaporation and for the turbulent homogenization. In the model, these scales are derived locally based on the subgrid-scale turbulent kinetic energy, spatial scale of cloudy filaments, mean cloud droplet radius, and humidity of the cloud-free air entrained into a cloud, all predicted by the LES model. The model reproduces contrasting macrophysical and microphysical characteristics of the cumulus and stratocumulus cloud layers. Simulated subgrid-scale turbulent mixing within the cumulus layer and near the stratocumulus top is on average quite inhomogeneous, but varies significantly depending on the local conditions.

Frontogenesis and frontal arrest of a dense filament in the oceanic surface boundary layer

2017 ◽  
Vol 837 ◽  
pp. 341-380 ◽  
Author(s):  
Peter P. Sullivan ◽  
James C. McWilliams
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Shear Instability ◽  
Upper Ocean ◽  
Surface Boundary ◽  
Horizontal Shear ◽  
Boundary Layer Turbulence ◽  
Filament Axis ◽  
Small Width ◽  
The Cross

The evolution of upper ocean currents involves a set of complex, poorly understood interactions between submesoscale turbulence (e.g. density fronts and filaments and coherent vortices) and smaller-scale boundary-layer turbulence. Here we simulate the lifecycle of a cold (dense) filament undergoing frontogenesis in the presence of turbulence generated by surface stress and/or buoyancy loss. This phenomenon is examined in large-eddy simulations with resolved turbulent motions in large horizontal domains using${\sim}10^{10}$grid points. Steady winds are oriented in directions perpendicular or parallel to the filament axis. Due to turbulent vertical momentum mixing, cold filaments generate a potent two-celled secondary circulation in the cross-filament plane that is frontogenetic, sharpens the cross-filament buoyancy and horizontal velocity gradients and blocks Ekman buoyancy flux across the cold filament core towards the warm filament edge. Within less than a day, the frontogenesis is arrested at a small width,${\approx}100~\text{m}$, primarily by an enhancement of the turbulence through a small submesoscale, horizontal shear instability of the sharpened filament, followed by a subsequent slow decay of the filament by further turbulent mixing. The boundary-layer turbulence is inhomogeneous and non-stationary in relation to the evolving submesoscale currents and density stratification. The occurrence of frontogenesis and arrest are qualitatively similar with varying stress direction or with convective cooling, but the detailed evolution and flow structure differ among the cases. Thus submesoscale filament frontogenesis caused by boundary-layer turbulence, frontal arrest by frontal instability and frontal decay by forward energy cascade, and turbulent mixing are generic processes in the upper ocean.

Experiments on Flame Flashback in a Quasi-2D Turbulent Wall Boundary Layer for Premixed Methane-Hydrogen-Air Mixtures

2010 ◽  
Author(s):  
Christian Eichler ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Turbulent Flows ◽  
Turbulent Transport ◽  
Wall Friction ◽  
Evaluation Procedure ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Flame Flashback ◽  
Turbulent Wall

Premixed combustion of hydrogen-rich mixtures involves the risk of flame flashback through wall boundary layers. For laminar flow conditions, the flashback mechanism is well understood and is usually correlated by a critical velocity gradient at the wall. Turbulent transport inside the boundary layer considerably increases the flashback propensity. Only tube burner setups have been investigated in the past and thus turbulent flashback limits were only derived for a fully-developed Blasius wall friction profile. For turbulent flows, details of the flame propagation in proximity to the wall remain unclear. This paper presents results from a new experimental combustion rig, apt for detailed optical investigations of flame flashbacks in a turbulent wall boundary layer developing on a flat plate and being subject to an adjustable pressure gradient. Turbulent flashback limits are derived from the observed flame position inside the measurement section. The fuels investigated cover mixtures of methane, hydrogen and air at various mixing ratios. The associated wall friction distributions are determined by RANS computations of the flow inside the measurement section with fully resolved boundary layers. Consequently, the interaction between flame back pressure and incoming flow is not taken into account explicitly, in accordance with the evaluation procedure used for tube burner experiments. The results are compared to literature values and the critical gradient concept is reviewed in light of the new data.

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