Onset conditions for vortex breakdown in supersonic flows

2018 ◽  
Vol 840 ◽  
Author(s):  
Toshihiko Hiejima
Keyword(s):  
Mach Number ◽  
Numerical Simulations ◽  
Stagnation Point ◽  
Vortex Breakdown ◽  
Three Dimensional ◽  
Supersonic Flows ◽  
Numerical Results ◽  
Comprehensive Approach ◽  
Onset Condition ◽  
Swirl Parameter

This study proposes an onset condition of shock-free supersonic vortex breakdown from the axial momentum variation, which applies in the presence or absence of a stagnation point. The condition is derived from a comprehensive approach to vortex breakdown. Supersonic breakdown appeared when the swirl parameter and Mach number were small. Moreover, bubble-type breakdowns with a stagnation point, which occur in subsonic conditions, could not occur under the supersonic condition in the present analysis. The predicted breakdowns under this condition were consistent with the results of the three-dimensional numerical simulations for Mach numbers ranging from 1.5 to 5.0. Supersonic vortex breakdowns were clearly captured by the helicity contours in the numerical results. The threshold of the downstream Mach number required for spiral breakdown with no stagnation point was also theoretically derived and verified in numerical results. These findings provide new insights into vortex breakdown in supersonic flows.

Dye visualization near a three-dimensional stagnation point: application to the vortex breakdown bubble

2009 ◽  
Vol 622 ◽  
pp. 177-194 ◽  
Author(s):  
M. BRØNS ◽  
M. C. THOMPSON ◽  
K. HOURIGAN
Keyword(s):  
Stagnation Point ◽  
Vortex Breakdown ◽  
Axisymmetric Flow ◽  
Three Dimensional ◽  
Planck Equation ◽  
Meridional Plane ◽  
Low Reynolds Number Flows ◽  
Dye Visualization ◽  
Visualization Techniques ◽  
Reynolds Number Flows

An analytical model, based on the Fokker–Planck equation, is constructed of the dye visualization expected near a three-dimensional stagnation point in a swirling fluid flow. The model is found to predict dye traces that oscillate in density and position in the meridional plane in which swirling flows are typically visualized. Predictions based on the model are made for the steady vortex breakdown bubble in a torsionally driven cylinder and compared with computational fluid dynamics predictions and experimental observations. Previous experimental observations using tracer visualization techniques have suggested that even for low-Reynolds-number flows, the steady vortex breakdown bubble in a torsionally driven cylinder is not axisymmetric and has an inflow/outflow asymmetry at its tail. Recent numerical and theoretical studies show that the asymmetry of the vortex breakdown bubble, and consequently its open nature, can be explained by the very small imperfections that are present in any experimental rig. Distinct from this, here it is shown that even for a perfectly axisymmetric flow and breakdown bubble, the combined effect of dye diffusion and the inevitable small errors in the dye injection position lead to the false perception of an open bubble structure with folds near the lower stagnation point. Furthermore, the asymmetries in the predicted flow structures can be remarkably similar to those observed in flow observations and computational predictions with geometric asymmetries of the rig. Thus, when interpreting dye-visualization patterns in steady flow, even if axisymmetric flow can be achieved, it is important to take into account the relative diffusivity of the dye and the accuracy of its injection.

Numerical Simulations of Sloshing in Rectangular Tanks

2006 ◽  
Author(s):  
Samuel R. Ransau ◽  
Ernst W. M. Hansen
Keyword(s):  
Numerical Simulations ◽  
Small Amplitude ◽  
Three Dimensional ◽  
Numerical Results ◽  
Experimental Results ◽  
Non Linear ◽  
Forced Excitation

Simulations of two- and three-dimensional sloshing in rectangular tanks are performed using the commercial CFD code FLOW3D. Small amplitude freely oscillating sloshing and non-linear sloshing due to forced excitation were investigated. The results are compared to both experimental results and other numerical results; and tests are made with different grids. The purpose of this study was the validation of the new VOF algorithm under development at Flow Science and implemented in FLOW3D.

scholarly journals Numerical Simulations of Advanced Transonic Compressor Stages Using an Unsteady Quasi-Three-Dimensional Flow Solver

1995 ◽  
Author(s):  
Gerald J. Micklow ◽  
J. Paul Sauve ◽  
Karthikeyan Shivaraman
Keyword(s):  
Numerical Simulations ◽  
Numerical Scheme ◽  
Stokes Equations ◽  
Computing Time ◽  
Three Dimensional ◽  
Axial Flow ◽  
Numerical Results ◽  
Compressor Stage ◽  
Transonic Compressor ◽  
Exact Geometry

This study presents the results of numerical simulations of single stage transonic axial-flow compressors. The numerical scheme used solves the unsteady quasi-three-dimensional thin-layer Navier-Stokes equations. In the first part of the study, the validation of the numerical scheme for advanced transonic axial-flow compressor stages is presented. The results of a numerical simulation are compared to an experimentally tested transonic compressor stage of DFVLR. Further simulations are performed on an advanced transonic compressor stage design to investigate the effect of airfoil geometry re-scaling, in order to save computing time, on the numerical results. Two cases are simulated: a modified geometry where less stator blades are simulated and an exact geometry where the exact geometry is modeled. Good agreement is obtained between the experimental and numerical results for the first test case, indicating the validity of the quasi-three dimensional method. The last two simulations show that any significant re-scaling of the stage geometry will have an adverse effect on overall results. All of the simulations show that the unsteady rotor-stator interactions have a significant effect on stage performance.

Effects of stator splitter blades on aerodynamic performance of a single-stage transonic axial compressor

2020 ◽  
Vol 14 (4) ◽  
pp. 7369-7378
Author(s):  
Ky-Quang Pham ◽  
Xuan-Truong Le ◽  
Cong-Truong Dinh
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Aerodynamic Performance ◽  
Numerical Results ◽  
Single Stage ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Operating Stability ◽  
Length Coverage

Splitter blades located between stator blades in a single-stage axial compressor were proposed and investigated in this work to find their effects on aerodynamic performance and operating stability. Aerodynamic performance of the compressor was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations using the k-e turbulence model with a scalable wall function. The numerical results for the typical performance parameters without stator splitter blades were validated in comparison with experimental data. The numerical results of a parametric study using four geometric parameters (chord length, coverage angle, height and position) of the stator splitter blades showed that the operational stability of the single-stage axial compressor enhances remarkably using the stator splitter blades. The splitters were effective in suppressing flow separation in the stator domain of the compressor at near-stall condition which affects considerably the aerodynamic performance of the compressor.

Using Ansys for Design and Numerical Study of a Specific Fixed Wing UAV

2018 ◽  
Vol 55 (4) ◽  
pp. 652-657 ◽  
Author(s):  
Gabriel Murariu ◽  
Razvan Adrian Mahu ◽  
Adrian Gabriel Murariu ◽  
Mihai Daniel Dragu ◽  
Lucian P. Georgescu ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Unmanned Aerial Vehicle ◽  
Numerical Study ◽  
Flight Time ◽  
Cluster System ◽  
Numerical Results ◽  
Operational Performance ◽  
Gliding Flight ◽  
Aerial Vehicle ◽  
Constant Altitude

This article presents the design of a specific unmanned aerial vehicle UAV prototype own building. Our UAV is a flying wing type and is able to take off with a little boost. This system happily combines some major advantages taken from planes namely the ability to fly horizontal, at a constant altitude and of course, the great advantage of a long flight-time. The aerodynamic models presented in this paper are optimized to improve the operational performance of this aerial vehicle, especially in terms of stability and the possibility of a long gliding flight-time. Both aspects are very important for the increasing of the goals� efficiency and for the getting work jobs. The presented simulations were obtained using ANSYS 13 installed on our university� cluster system. In a next step the numerical results will be compared with those during experimental flights. This paper presents the main results obtained from numerical simulations and the obtained magnitudes of the main flight coefficients.

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