Effect of Suction on the Stability of Supersonic Boundary Layers. Part II—First-Mode Waves

1991 ◽  
Vol 113 (4) ◽  
pp. 598-601 ◽  
Author(s):  
J. A. Masad ◽  
A. H. Nayfeh ◽  
A. A. Al-Maaitah
Keyword(s):  
Boundary Layers ◽  
Mass Flux ◽  
Growth Rates ◽  
Two Dimensional ◽  
Viscous Instability ◽  
Dimensional Boundary ◽  
Mach Numbers ◽  
The Stability

The effect of suction on the first mode of instability of compressible two-dimensional boundary layers is investigated. Suction is found to be more effective in stabilizing the viscous instability, and hence it is more effective at low Mach numbers. Suction decreases the amplification rates at all frequencies and narrows down the band of unstable frequencies. Moreover, for a given frequency, suction decreases the amplification rates at all streamwise locations. Variations of the growth rates of the most amplified first-mode waves with mass flux are found to be almost linear.

Effect of Suction on the Stability of Supersonic Boundary Layers. Part I—Second-Mode Waves

1991 ◽  
Vol 113 (4) ◽  
pp. 591-597 ◽  
Author(s):  
A. A. Al-Maaitah ◽  
A. H. Nayfeh ◽  
J. A. Masad
Keyword(s):  
Mach Number ◽  
Boundary Layers ◽  
Mass Flux ◽  
Two Dimensional ◽  
Second Mode ◽  
Wave Numbers ◽  
Stabilizing Effect ◽  
Dimensional Boundary ◽  
The Stability ◽  
And Shifts

The effect of suction on the second (Mack) mode of instability in supersonic and hypersonic two-dimensional boundary layers is investigated. The results show that suction has a stabilizing effect on these waves; it reduces the peak amplification and shifts it toward a higher frequency. In the presence of suction, the most amplified Mack mode remains two-dimensional. The effectiveness of suction in stabilizing Mack waves decreases as the Mach number increases. Variations of the growth rates of the most amplified Mack mode and the corresponding frequencies and wave numbers with mass flux are found to be almost linear. The frequencies and wave numbers corresponding to the most amplified Mack mode increase by increasing the suction level.

On Estimates for Growth Rates of Unstable Azimuthal Disturbances in the Stability Problem of Swirling Flows with Radius- Dependent Density

2017 ◽  
Vol 13 (3) ◽  
pp. 1-12
Author(s):  
Halle Dattu Malai Subbiah
Keyword(s):  
Growth Rate ◽  
Growth Rates ◽  
Stability Problem ◽  
Variable Density ◽  
Swirling Flows ◽  
Wave Number ◽  
Two Dimensional ◽  
Azimuthal Wave Number ◽  
The Stability ◽  
Dependent Density

Estimates for the growth rate of unstable two-dimensional disturbances to swirling flows with variable density are obtained and as a consequence it is proved that the growth rate tends to zero as the azimuthal wave number tends to infinity for two classes of basic flows.

scholarly journals Damage zone propagation and support pressure estimation around two access tunnels of the Barapukuria coalmine in Bangladesh: a two-dimensional numerical modeling approach

2015 ◽  
Vol 3 (2) ◽  
pp. 14
Author(s):  
Md. Rafiqul Islam ◽  
Mohammed Omar Faruque ◽  
Ryuichi Shinjo
Keyword(s):  
Damage Zone ◽  
Support Pressure ◽  
Two Dimensional ◽  
Weak Rocks ◽  
Strength Factor ◽  
Internal Support ◽  
Dimensional Boundary ◽  
Pressure Estimation ◽  
The Stability ◽  
Two Stages

<p>The present study uses a two-dimensional boundary element method (BEM) numerical analysis to predict damage zone propagation associated with the required support pressure estimation around the two access tunnels of Barapukuria coalmine in northwest Bangladesh. Two tunnels at different depths are presented here. The stability of the two tunnels that was driven through the weak rocks' strata of Gondwana formation is examined at depths below the surface 290 m and 453 m. The two tunnels involve horseshoe-shaped design. The shallower tunnels, which are located below the surface 290 m, are presented by model A. The deeper tunnels, which are located below the surface 453 m, are presented by model B. Both tunnels are horseshoe-shaped with a height and span of about 4.5 m and 4 m, respectively. The modeling analysis was carried out in two stages to predict the damage zone and required support pressure. The first stage considered the model without support installation. The second stage measured the model with non-uniform internal support pressure installation. It is reasonable to mention that prior and subsequent to the support pressure estimation, three important parameters, like- strength factor, failure trajectories, and deformation boundaries in the vicinity of the two tunnels have been computed properly. Final results reveal that the strength factor values ranged from 0.33 to 0.99 would create the intense deformation at the roof and sidewalls. The damage zone would be extended from 0.64 to 0.74 m towards the roof and sidewalls. The damage zone would be ranged from 1.95 to 2.21 m, for shallower and deeper tunnels, respectively. For shallower tunnels, the required support pressure would be ranged from 4.0 to 9.0 MPa. For deeper tunnels, the essential support pressure would be ranged from 7.0 to 14 MPa.</p>

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