Effect of Destabilizing Heating on Go¨rtler Vortices

1985 ◽  
Vol 107 (4) ◽  
pp. 877-882 ◽  
Author(s):  
Y. Kamotani ◽  
J. K. Lin ◽  
S. Ostrach
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Nonlinear Effects ◽  
Experimental Investigations ◽  
Wave Form ◽  
Sinusoidal Wave ◽  
Lateral Direction ◽  
Vortex Instability ◽  
Nonlinear Region ◽  
Layer Flow

Experimental investigations of the effect of destabilizing heating on the vortex instability in a laminar boundary-layer flow of air along a concave surface are reported. The ranges of the parameters studied herein are Gr (Grashof number) from 0 to 70 and G (Go¨rtler number) from 0.46 to 9.0. The wavelength of the vortices remains unchanged with heating but the strength of the vortices is enhanced by heating. The amplitude of the vortices increases almost exponentially with the combined parameter (G2 + f Gr)1/2, where f is found to be between 0.3 and 0.4, until the nonlinear effects become important. In the nonlinear region the original sinusoidal wave form of the vortices becomes distorted and they meander in the lateral direction.

Vortex Instability in Buoyancy-Induced Flow over Inclined Heated Surfaces in Porous Media

1979 ◽  
Vol 101 (4) ◽  
pp. 660-665 ◽  
Author(s):  
C. T. Hsu ◽  
Ping Cheng
Keyword(s):  
Boundary Layer ◽  
Inclination Angle ◽  
Boundary Layer Flow ◽  
Heated Surface ◽  
Wave Number ◽  
Heated Plate ◽  
Local Similarity ◽  
Linear Temperature ◽  
Vortex Instability ◽  
Layer Flow

A linear stability analysis is performed for the study of the onset of vortex instability in free convective flow over an inclined heated surface in a porous medium. The undisturbed state is assumed to be the steady two-dimensional buoyancy-induced boundary layer flow which is characterized by a non-linear temperature profile. By a scaling argument, it is shown that the length scales of disturbances are smaller than those for the undisturbed boundary layer flow, thus, confirming the so-called “bottling effects” whereby the disturbances are confined within the boundary layer. By neglecting the lowest order terms in the three-dimensional disturbances equations, the simplified equations are solved based on the local similarity approximations, wherein the disturbances are assumed to have a weak dependence in the streamwise direction. The resulting eigenvalue problem is solved numerically. The critical parameter and the critical wave number of disturbances at the onset of vortex instability are computed for different prescribed wall temperature distribution of the inclined surface. It is found that the larger the inclination angle with respect to the vertical, the more susceptible is the flow for the vortex mode of disturbances; and in the limit of zero inclination angle (i.e., a vertical heated plate) the flow is stable for this form of disturbances.

On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development, and Boundary Layer Flow in An Annular Low-Pressure Turbine Cascade: An Experimental Investigation

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Martin Sinkwitz ◽  
Benjamin Winhart ◽  
David Engelmann ◽  
Francesca di Mare ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Measurement Data ◽  
Separated Flow ◽  
Low Pressure ◽  
Experimental Investigations ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Layer Flow

The experimental results reported in this contribution address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile low-pressure turbine (LPT) stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, nonuniform, increasing pitch across the span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening, and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.

On the Periodically Unsteady Interaction of Wakes, Secondary Flow Development and Boundary Layer Flow in an Annular LPT Cascade: Part 1 — Experimental Investigation

2018 ◽  
Author(s):  
Martin Sinkwitz ◽  
Benjamin Winhart ◽  
David Engelmann ◽  
Francesca di Mare ◽  
Ronald Mailach
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Boundary Layer Flow ◽  
Measurement Data ◽  
Separated Flow ◽  
Experimental Investigations ◽  
Suction Surface ◽  
Time Resolved ◽  
Unsteady Interaction ◽  
Layer Flow

The results reported in this two-part — combined experimental and numerical — paper address the time-dependent impact of periodically unsteady wakes on the development of profile and end wall boundary layers and consequently on the secondary flow system. Experimental investigations are conducted on an annular 1.5 stage axial turbine rig at Ruhr-Universität Bochum’s Chair of Thermal Turbomachines and Aeroengines. The object under investigation is a modified T106 profile LPT stator row at a representative exit flow Reynolds number of 200,000. By making use of an annular geometry instead of a linear cascade, the influence of curvilinear end walls, non-uniform, increasing pitch across span and radial flow migration can be represented. Incoming wakes are generated by a variable-speed driven rotor equipped with cylindrical bars. Special emphasis is put on the wake-induced recurrent formation, suppression, weakening and displacement of individual vortices and separated flow regimes. For this, based on a comprehensive set of time-resolved measurement data, the interaction of impinging bar wakes and boundary layer flow and thus separation and its periodic manipulation along the passage end walls and on the blade suction surface are studied within the frequency domain.

scholarly journals Effect of Variable Viscosity on Vortex Instability of Non-Darcy Mixed Convection Boundary Layer Flow Adjacent to a Nonisothermal Horizontal Surface in a Porous Medium

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
A. M. Elaiw ◽  
A. A. Bakr ◽  
M. A. Alghamdi ◽  
F. S. Ibrahim
Keyword(s):  
Boundary Layer ◽  
Porous Medium ◽  
Mixed Convection ◽  
Boundary Layer Flow ◽  
Variable Viscosity ◽  
Finite Difference Schemes ◽  
Convection Boundary Layer ◽  
Vortex Instability ◽  
Convection Boundary ◽  
Layer Flow

We study the effect of variable viscosity on the flow and vortex instability for non-Darcy mixed convection boundary layer flow on a nonisothermal horizontal plat surface in a saturated porous medium. The variation of viscosity is expressed as an exponential function of temperature. The analysis of the disturbance flow is based on linear stability theory. The base flow equations and the resulting eigenvalue problem are solved using finite difference schemes. It is found that the variable viscosity effect enhances the heat transfer rate and destabilizes the flow for liquid heating, while the opposite trend is true for gas heating.

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