Three-Dimensional Forced Convection in Plane Symmetric Sudden Expansion

2004 ◽  
Vol 126 (5) ◽  
pp. 836-839 ◽  
Author(s):  
J. H. Nie and ◽  
B. F. Armaly
Keyword(s):  
Nusselt Number ◽  
Forced Convection ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Outer Edge ◽  
Sudden Expansion ◽  
Recirculation Flow ◽  
Plane Symmetric ◽  
Laminar Forced Convection

Simulations of three-dimensional laminar forced convection in a plane symmetric sudden expansion are presented for Reynolds numbers where the flow is steady and symmetric. A swirling “jetlike” flow develops near the sidewalls in the separating shear layer, and its impingement on the stepped wall is responsible for the maximum that develops in the Nusselt number adjacent to the sidewalls and for the reverse flow that develops in that region. The maximum Nusselt number on the stepped wall is located inside the primary recirculation flow region and its location does not coincide with the jetlike flow impingement region. The results reveal that the location where the streamwise component of wall shear stress is zero on the stepped walls does not coincide with the outer edge of the primary recirculation flow region near the sidewalls.

Laminar Mixed Convection Adjacent to Three-Dimensional Backward-Facing Step

2001 ◽  
Vol 124 (1) ◽  
pp. 209-213 ◽  
Author(s):  
A. Li and ◽  
B. F. Armaly
Keyword(s):  
Nusselt Number ◽  
Mixed Convection ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
The Other ◽  
Backward Facing Step ◽  
Number Range ◽  
Grashof Number ◽  
Recirculation Flow

Simulations of three-dimensional laminar buoyancy-assisting mixed convection adjacent to a backward-facing step in a vertical rectangular duct are presented to demonstrate the influence of Grashof number on the distributions of the Nusselt number, and the reverse flow regions that develop adjacent to the duct’s walls. The Reynolds number, and duct’s geometry are kept constant: heat flux at the wall downstream from the step is kept uniform but its magnitude varied to cover a Grashof number range of 0–4000; all the other walls in the duct are kept at adiabatic condition; and the flow, upstream of the step, is treated as fully developed and isothermal. Increasing the Grashof number results in increasing the Nusselt number; the size of the secondary recirculation flow region adjacent to the stepped wall; the size of the reverse flow region adjacent to the sidewall and the flat wall; and the spanwise flow from the sidewall toward the center of the duct. On the other hand, the size of the primary recirculation flow region adjacent to the stepped wall decreases and detaches partially from the heated stepped wall as the Grashof number increases. Details are presented and discussed.

Three-Dimensional Forced Convection Flow in Plane Symmetric Sudden Expansion

2003 ◽  
Author(s):  
J. H. Nie ◽  
B. F. Armaly
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Friction Coefficient ◽  
Forced Convection ◽  
Three Dimensional ◽  
Sudden Expansion ◽  
Recirculation Region ◽  
Number Range ◽  
Plane Symmetric ◽  
Reynolds Number Range

Simulations of three-dimensional flow and heat transfer in laminar incompressible forced convection in plane symmetric sudden expansion (backward-facing step in rectangular duct) are presented for different Reynolds numbers. The duct’s downstream (H) and upstream (h) heights are 0.04m and 0.02m, respectively, thus providing a step height (S) of 0.01m and an expansion ratio of 2. The duct’s width (W) is 0.08m, thus resulting in an aspect ratio of 4 before and 2 after the expansion, respectively. The incoming flow is considered to be isothermal, hydro-dynamically steady and fully developed. Uniform and constant heat flux is specified on the stepped walls, while the other walls are treated as adiabatic surfaces. The flow appears to be symmetric for the low Reynolds number range that is considered in this study (Re=150). A “jet-like” flow develops near the sidewall and its impingement on the stepped wall creates a swirling flow inside the primary recirculation region adjacent to the stepped wall, and that is responsible for creating a maximum in the Nusselt number distribution. The results reveal that the location where the streamwise component of wall shear stress is zero on the stepped wall does not coincide with the location of the outer edge of the primary recirculation region, especially in the region near the sidewall. Neither one of these boundary lines represents the reattachment region of the separated flow in the region adjacent to the sidewall. The maximum Nusselt number on the stepped wall is located inside the primary recirculation region and is not identical to the “jet-like” flow impingement point. The maximum friction coefficient on the stepped wall is located inside the primary recirculation region, and it is at the center of the duct for the Reynolds number range considered in this study. The minimum friction coefficient on the stepped wall is located at the impingement of the “jet-like” flow.

LAMINAR FORCED CONVECTION IN THREE-DIMENSIONAL DUCT FLOWS

1988 ◽  
Vol 13 (4) ◽  
pp. 451-466 ◽  
Author(s):  
C. Nonino ◽  
S. Del Giudice ◽  
G. Comini
Keyword(s):  
Forced Convection ◽  
Three Dimensional ◽  
Laminar Forced Convection

The role of rotary motion on vortices in reverse flow

2019 ◽  
Vol 880 ◽  
pp. 723-742 ◽  
Author(s):  
Luke R. Smith ◽  
Yong Su Jung ◽  
James D. Baeder ◽  
Anya R. Jones
Keyword(s):  
Vortex Dynamics ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Vortex Method ◽  
Forward Flight ◽  
Vorticity Transport ◽  
Rotating Wing ◽  
Rotary Wing

The physics of a rotary wing in forward flight are highly complex, particularly when flow separation is involved. The purpose of this work is to assess the role of three-dimensional (3-D) vortex dynamics, with a focus on Coriolis forces, in the evolution of vortices in the reverse flow region of a rotating wing. High-fidelity numerical simulations were performed to recreate the flow about a representative rotating wing in forward flight. A vorticity transport analysis was performed to quantify and compare the magnitudes of 2-D flow physics, vortex tilting and Coriolis effects in the resulting flow fields. Three-dimensional vortex dynamics was found to have a very small impact on the growth and behaviour of vortices in the reverse flow region; in fact, the rate of vortex growth was successfully modelled using a simple 2-D vortex method. The small role of 3-D physics was attributed to the Coriolis and vortex tilting terms being approximately equal and opposite to one another. This ultimately lead to vortex behaviour that more closely resembled a surging wing as opposed to a conventional rotating wing, a feature unique to the reverse flow region.

Aerodynamic Behavior of Asymmetric Jets in 3-D Furnaces

1994 ◽  
Author(s):  
F. M. El-Mahallawy ◽  
M. A. Hassan ◽  
M. A. Ismail ◽  
H. Zafan
Keyword(s):  
Numerical Simulation ◽  
Flow Pattern ◽  
Numerical Experiments ◽  
Recirculation Zone ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Stabilization Method ◽  
Flow Features

The purpose of this paper is to present and evaluate numerical experiments illustrating the flow features in a 3-D furnace utilizing unconventional asymmetrical jet that creates natural recirculation zone. The numerical simulation of this aerodynamic stabilization method have unveiled the three-dimensional nature of the flow pattern which possesses a quite large reverse flow region. The size and strength of the built recirculation zone would be capable of stabilizing the burning of low-quality fuels.

Pressure-Probe Interference in a Vortex Flow

1978 ◽  
Vol 5 (2) ◽  
pp. 106-110
Author(s):  
O.O. Mojola
Keyword(s):  
Vortex Flow ◽  
Static Pressure ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Flow Region ◽  
Pressure Probe ◽  
Pressure Data ◽  
Pressure Sensing ◽  
Recirculation Flow ◽  
Made In

This paper examines the sensitivity of vortex-flows to disturbances arising from the insertion of conventional pressure-sensing probes into the flows. With a wide variety of pitot-tubes, static-pressure probes, and transverse-cylinder yawmeters, measurements were made in the vortex (recirculation) flow region of a separated, three-dimensional, turbulent boundary layer upstream of a vertical wall. The measurements, which included both local and surface pressure data, have been analysed to reveal how the shape, size, and alignment of probes independently and collectively contribute to the probe interference.

Analysis of the Flow in Vaneless Diffusers With Large Width-to-Radius Ratios

1996 ◽  
Author(s):  
Hua-Shu Dou ◽  
Shimpei Mizuki
Keyword(s):  
Boundary Layer ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Rotating Stall ◽  
Wake Flow ◽  
Layer Versus ◽  
Dimensional Boundary ◽  
Vaneless Diffusers ◽  
Large Width

The flow in vaneless diffusers with large width-to-radius ratios is analyzed by using three-dimensional boundary-layer theory. The variations of the wall shear angle in the layer and the separation radius of the turbulent boundary layer versus various parameters are calculated and compared with experimental data. The effect of the separation point on the performance of vaneless diffusers and the mechanism of rotating stall are discussed. It is concluded that when the flow rate becomes very low, the reverse flow zone on the diffuser walls extends toward the entry region of diffusers. When the rotating jet-wake flow with varying total pressure passes through the reverse flow region near the impeller outlet, rotating stall is generated. The influences of the radius ratio on the reverse flow occurrence as well as on the overall performance are also discussed.

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