Effect of Wave Instabilities in Thermal and Solutal Mixing of Double-Diffusive Opposed Jets Impinging in a Passive-Mixer

2021 ◽  
Author(s):  
Saleem Anwar Khan ◽  
Nadeem Hasan
Keyword(s):  
Unsteady Flow ◽  
Flow Regime ◽  
Landau Theory ◽  
Travelling Waves ◽  
Unsteady Flows ◽  
Boussinesq Approximation ◽  
Bulk Velocity ◽  
Flow Mode ◽  
Passive Mixer ◽  
Neutral Curves

Abstract 2-D numerical experiments are performed to investigate the flow instabilities and mixing of different non-isothermal counterflowing jets in a Passive-Mixer. The fluid is modelled as a binary mixture with thermal and solutal buoyancy effects considered through the Boussinesq approximation. The streams are arranged in a thermal and solutal buoyancy aiding configuration. Computations are carried out for three different ratios of the upper jet bulk velocity to the lower jet bulk velocity (VR), namely, VR = 0.5, 1.0 and 2. Within the parametric domain of RiT and RiC defined by region (RiT + RiC) = 3, the instability causing transition from steady to unsteady flow regime is observed for VR = 1 and 2 while no transition is found to occur at VR = 0.5. Using Landau theory, it is established that the transition from steady to unsteady flow regime is a supercritical Hopf bifurcation. A complete regime map identifying the steady and unsteady flow regimes, within the parametric space of the present study, is obtained by plotting the neutral curves of RiC and RiT (obtained using Landau theory) for different values of VR. POD analysis of the unsteady flows at VR = 1, establishes the presence of standing waves. However, for VR = 2, the presence of degenerate pairs in the POD eigenspectrum ascertains the presence of travelling waves in the unsteady flows. The standing wave unsteady flow mode is found to yield the highest rate of mixing.

Grid adaptation for unsteady flow computations

1997 ◽  
Vol 211 (4) ◽  
pp. 237-250 ◽  
Author(s):  
C B Allen
Keyword(s):  
Unsteady Flow ◽  
Unsteady Flows ◽  
Processing Unit ◽  
Flow Solver ◽  
Transfinite Interpolation ◽  
Central Processing ◽  
Grid Adaptation ◽  
Euler Flows ◽  
Adaptation Procedure ◽  
Grid Points

A grid adaptation procedure suitable for use during unsteady flow computations is described. Transfinite interpolation is used to generate structured grids for the computation of steady and unsteady Euler flows past aerofoils. This technique is well suited to unsteady flows, since instantaneous grid positions and speeds required by the flow solver are available directly from the algebraic mapping. A different approach to grid adaptation is described, wherein adaptation is performed by redistributing the interpolation parameters, instead of the physical grid positions. This results in the adapted grid positions, and hence speeds, still being available algebraically. Grid adaptation during an unsteady computation is performed continuously by imposing an ‘adaptation velocity’ on grid points, thereby applying the adaptation over several time steps and avoiding the interpolation of the solution from one grid to another, which is associated with instantaneous adaptation. For both steady and unsteady flows the adapted grid technique is shown to produce sharper shock resolution for a very small increase in CPU (central processing unit) requirements.

Predicting Bladerow Interactions Using a Multistage Time-Linearized Navier-Stokes Solver

2003 ◽  
Vol 125 (1) ◽  
pp. 25-32 ◽  
Author(s):  
W. Ning ◽  
Y. S. Li ◽  
R. G. Wells
Keyword(s):  
Unsteady Flow ◽  
Frequency Domain ◽  
Test Data ◽  
Computational Efficiency ◽  
Unsteady Flows ◽  
Navier Stokes ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Flow Solver ◽  
Time Marching

A multistage frequency domain (time-linearized/nonlinear harmonic) Navier-Stokes unsteady flow solver has been developed for predicting unsteady flows induced by bladerow interactions. In this paper, the time-linearized option of the solver has been used to analyze unsteady flows in a subsonic turbine test stage and the DLR transonic counter-rotating shrouded propfan. The numerical accuracy and computational efficiency of the time-linearized viscous methods have been demonstrated by comparing predictions with test data and nonlinear time-marching solutions for these two test cases. It is concluded that the development of efficient frequency domain approaches enables unsteady flow predictions to be used in the design cycles to tackle aeromechanics problems.

scholarly journals Unsteady Flow of a Nanofluid over a Sphere with Nonlinear Boussinesq Approximation

2019 ◽  
Vol 33 (2) ◽  
pp. 343-355 ◽  
Author(s):  
B. Vasu ◽  
Rama Subba Reddy Gorla ◽  
O. Anwar Bég ◽  
P. V. S. N. Murthy ◽  
V. R. Prasad ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Boussinesq Approximation

Numerical Investigation of Sub-Iteration Criterions for Unsteady Flow Computations with Dual-Time Method

2013 ◽  
Vol 432 ◽  
pp. 189-195
Author(s):  
Guang Ning Li ◽  
Min Xu
Keyword(s):  
Unsteady Flow ◽  
Unsteady Flows ◽  
Numerical Results ◽  
Iteration Step ◽  
Convergence Criterion ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Physical Time ◽  
New Criterion

The convergence of sub-iteration with the dual-time method is very important for the prediction of unsteady flow field. The influence of sub-iteration step number, criterion of sub-iteration convergence and the choice of physical time step size on the calculation results are discussed by solving of the two-dimensional unsteady Euler equations. A new convergence criterion (named residual criterion) of sub-iteration for unsteady flows is proposed, and the unsteady flow test case AGARD-CT5 is calculated to verify the new criterion. The results show that, with the same criterion of sub-iteration, the results from different physical time step sizes are in agreement with each other. The difference between the experiment data and the numerical results are small, and if the sub-iteration criterion used is reasonable and small enough, the dependence of numerical results of unsteady flows on the physical time step will be decreased as possible. The new criterion of sub-iteration for dual-time step unsteady calculations can be used for engineering problem.

Predicting Bladerow Interactions Using a Multistage Time-Linearized Navier-Stokes Solver

2002 ◽  
Author(s):  
W. Ning ◽  
Y. S. Li ◽  
R. G. Wells
Keyword(s):  
Unsteady Flow ◽  
Frequency Domain ◽  
Test Data ◽  
Computational Efficiency ◽  
Unsteady Flows ◽  
Navier Stokes ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Flow Solver ◽  
Time Marching

A multistage frequency domain (time-linearized/nonlinear harmonic) Navier-Stokes unsteady flow solver has been developed for predicting unsteady flows induced by bladerow interactions. In this paper, the time-linearized option of the solver has been used to analyze unsteady flows in a subsonic turbine test stage and the DLR transonic counter-rotating shrouded propfan. The numerical accuracy and computational efficiency of the time-linearized viscous methods have been demonstrated by comparing predictions with test data and nonlinear time-marching solutions for these two test cases. It is concluded that the development of efficient frequency domain approaches enables unsteady flow predictions to be used in the design cycles to tackle aeromechanics problems.

Inviscid-Viscous Coupled Solution for Unsteady Flows Through Vibrating Blades: Part 2—Computational Results

1993 ◽  
Vol 115 (1) ◽  
pp. 101-109 ◽  
Author(s):  
L. He ◽  
J. D. Denton
Keyword(s):  
Unsteady Flow ◽  
Transonic Flow ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Computational Results ◽  
Flow Conditions ◽  
Viscous Effects ◽  
Blade Flutter ◽  
Coupled Solution

A quasi-three-dimensional inviscid-viscous coupled approached has been developed for unsteady flows around oscillating blades, as described in Part 1. To validate this method, calculations for several steady and unsteady flow cases with strong inviscid-viscous interactions are performed, and the results are compared with the corresponding experiments. Calculated results for unsteady flows around a biconvex cascade and a fan tip section highlight the necessity of including viscous effects in predictions of turbomachinery blade flutter at transonic flow conditions.

Inviscid-Viscous Coupled Solution for Unsteady Flows Through Vibrating Blades: Part 2 — Computational Results

1991 ◽  
Author(s):  
L. He ◽  
J. D. Denton
Keyword(s):  
Unsteady Flow ◽  
Transonic Flow ◽  
Unsteady Flows ◽  
Computational Results ◽  
Flow Conditions ◽  
Viscous Effects ◽  
Blade Flutter ◽  
Coupled Solution

A quasi 3-D inviscid-viscous coupled approach has been developed for unsteady flows around oscillating blades, as described in Part 1. To validate this method, calculations for several steady and unsteady flow cases with strong inviscid-viscous interactions are performed, and the results are compared with the corresponding experiments. Calculated results for unsteady flows around a bi-convex cascade and a fan tip section highlight the necessity of including viscous effects in predictions of turbomachinery blade flutter at transonic flow conditions.

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