Three-dimensional instabilities over a rectangular open cavity: from linear stability analysis to experimentation

2014 ◽  
Vol 748 ◽  
pp. 189-220 ◽  
Author(s):  
J. de Vicente ◽  
J. Basley ◽  
F. Meseguer-Garrido ◽  
J. Soria ◽  
V. Theofilis
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Linear Analysis ◽  
Main Flow ◽  
Open Cavity ◽  
Flow Structures ◽  
Cavity Flows ◽  
Final State ◽  
Wave Properties ◽  
Final Expression

AbstractThree-dimensional instabilities arising in open cavity flows are responsible for complex broad-banded dynamics. Existing studies either focus on theoretical properties of ideal simplified flows or observe the final state of experimental flows. This paper aims to establish a connection between the onset of the centrifugal instabilities and their final expression within the fully saturated flow. To that end, a linear three-dimensional modal instability analysis of steady two-dimensional states developing in an open cavity of aspect ratio $L/D=2$ (length over depth) is conducted. This analysis is performed together with an experimental study in the same geometry adding spanwise endwalls. Two different Reynolds numbers are investigated through spectral analyses and modal decomposition. The physics of the flow is thoroughly described exploiting the strengths of each methodology. The main flow structures are identified and salient space and time scales are characterised. Results indicate that the structures obtained from linear analysis are mainly consistent with the fully saturated experimental flow. The analysis also brings to light the selection and alteration of certain wave properties, which could be caused by nonlinearities or the change of spanwise boundary conditions.

Turbulent Mixing With Density Differences

2011 ◽  
Author(s):  
Jos Derksen
Keyword(s):  
Turbulent Mixing ◽  
Richardson Number ◽  
Kinematic Viscosity ◽  
Three Dimensional ◽  
Flow Regimes ◽  
Reynolds Numbers ◽  
Flow Structures ◽  
Three Dimensional Flow ◽  
Flow Equations ◽  
Miscible Liquids

Homogenization of initially segregated and stably stratified systems consisting of two miscible liquids with different density and the same kinematic viscosity in an agitated tank was studied computationally. Reynolds numbers were in the range of 3,000 to 12,000 so that it was possible to solve the flow equations without explicitly modeling turbulence. The Richardson number that characterizes buoyancy was varied between 0 and 1. The stratification clearly lengthens the homogenization process. Two flow regimes could be identified. At low Richardson numbers large, three-dimensional flow structures dominate mixing, as is the case in non-buoyant systems. At high Richardson numbers the interface between the two liquids largely stays intact. It rises due to turbulent erosion, gradually drawing down and mixing up the lighter liquid.

Evaluation of Compressor Blading With Blade End Slots and Full-Span Slots in a Highly Loaded Compressor Cascade

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Yumeng Tang ◽  
Yangwei Liu ◽  
Lipeng Lu
Keyword(s):  
Incidence Angle ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Main Flow ◽  
The Self ◽  
Flow Structures ◽  
Compressor Cascade ◽  
Corner Separation ◽  
High Incidence ◽  
Highly Loaded

Abstract Blade end slots were proposed to control corner separation in a highly loaded compressor cascade in our previous studies. This study focuses on the evaluation of compressor blading with blade end slots and full-span slots. First, the two-dimensional configuration performance is evaluated both for the datum and slotted profiles. The slotted configuration could effectively suppress separation, especially under positive incidence conditions when the separation is large. Thus, two three-dimensional blading with full-span slots and blade end slots (20% span height from the endwall) are compared. Results show that blading with full-span slots could effectively reduce the loss and enlarge pressure rise under relative high incidence angles, while blading with blade end slots could effectively reduce the loss and enlarge pressure rise above an incidence angle of −4 deg. Blading with slots alters the flow structures and reorganizes the flow in the blade end regions. The self-adaptive jets from the slots reenergize the low-momentum flow downstream and restrain its migration toward the mid-span, so that the corner separation is reduced and the performance is enhanced. The loss for the end slotted blade is lower than that of the full-span slotted blade under incidence angles within 4 deg. This is because the additional mixing loss of the jet and the main flow are caused by the full-span slots at the mid-span regions where the flow remains attached for the blade end slots.

Numerical Simulation of Incompressible Laminar Flow over Three-Dimensional Rectangular Cavities

2004 ◽  
Vol 126 (6) ◽  
pp. 919-927 ◽  
Author(s):  
H. Yao ◽  
R. K. Cooper ◽  
S. Raghunathan
Keyword(s):  
Reynolds Number ◽  
Incompressible Flow ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Cavity Flow ◽  
External Flow ◽  
Cavity Flows ◽  
Recirculating Flow ◽  
Deep Cavity ◽  
Shallow Cavity

This paper presents results of investigations of unsteady incompressible flow past three-dimensional cavities, where there is a complex interaction between the external flow and the recirculating flow inside the cavity. A computational fluid dynamics approach is used in the study. The simulation is based on the solution of the unsteady Navier-Stokes equations for three-dimensional incompressible flow by using finite difference schemes. The cavity is assumed to be rectangular in geometry, and the flow is assumed to be laminar. Typical results of computation are presented, showing the effects of the Reynolds number, cavity geometry, and inflow condition on the cavity flow fields. The results show that high Reynolds numbers, with deep cavity and shallow cavity flows can become unsteady with Kelvin-Helmholtz instability oscillations and exhibiting a three-dimensional nature, with Taylor-Go¨rtler longitudinal vortices on the floor and longitudinal vortex structures on the shear layer. At moderate Reynolds numbers the shallow cavity flow is more stable than deep cavity flows. For a given Reynolds number the flow structure is affected by the thickness of the inflow boundary layer with a significant interaction between the external flow and the recirculating flow inside the cavity.

On the modulating effect of three-dimensional instabilities in open cavity flows

2014 ◽  
Vol 759 ◽  
pp. 546-578 ◽  
Author(s):  
J. Basley ◽  
L. R. Pastur ◽  
F. Lusseyran ◽  
J. Soria ◽  
N. Delprat
Keyword(s):  
Shear Layer ◽  
Travelling Waves ◽  
Broad Band ◽  
Three Dimensional ◽  
High Energy ◽  
Open Cavity ◽  
Coupling Mechanism ◽  
Cavity Flows ◽  
Low Frequencies ◽  
Sustained Oscillations

AbstractOpen cavity flows are known to select and enhance locked-on modes or tones. High-energy self-sustained oscillations arise within the shear layer, impinging onto the trailing edge of the cavity. These self-sustained oscillations are subject to amplitude modulations (AMs) at multiple low frequencies. However, only a few studies have addressed the identification of the lowest modulating frequencies. The present work brings to light salient AMs of the shear layer waves and identifies their source as three-dimensional dynamics existing inside the cavity. Indeed, the recirculating inner flow gives rise to centrifugal instabilities, which entail broad-band frequencies down two orders of magnitude lower than those of the self-sustained oscillations. Using time-resolved PIV (TRPIV) in two planes, the nonlinearly saturated dynamics is analysed in both space and time by means of proper orthogonal decomposition, global Fourier decomposition and Hilbert–Huang transforms. The inner flow can be decomposed as three-dimensional waves carried by the main recirculation. Bicoherence distributions are computed to highlight the nonlinear interactions between these spanwise-travelling waves inside the cavity and the locked-on modes. The modulated envelope of the shear layer oscillations is extracted and investigated with regards to the inner-flow dynamics. Strong cross-correlations, in time rather than in space, reveal a global coupling mechanism, possibly related to the beating of the spanwise-travelling waves.

The Influence of Shrouded Stator Cavity Flows on the Aerodynamic Performance of a High-Speed Multistage Axial-Flow Compressor

2011 ◽  
Author(s):  
Dai Kato ◽  
Mai Yamagami ◽  
Naoki Tsuchiya ◽  
Hidekazu Kodama
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Axial Flow ◽  
Main Flow ◽  
Navier Stokes ◽  
Cavity Flows ◽  
Axial Flow Compressor ◽  
First Case ◽  
Flow Compressor ◽  
Unsteady Effects

This paper investigates numerically the effects of shrouded stator seal cavity flows on a high-speed, six-stage, advanced axial-flow compressor performance. Two cases of fully three-dimensional unsteady Reynolds-averaged Navier-Stokes simulations are performed. The first case includes only the main flow path without cavities, while the second case takes into account the effect of cavities by fully meshing and solving the seal cavity flows under each of the stator vanes. Both simulations included rotor blade tip clearances. The latter case showed 1.7 point degradation in efficiency from the first case. Contributors to the overall performance degradation, such as windage heating, mixing loss due to seal leakage flow with the main flow, and additional loss of the rotors and stators due to alteration in velocity triangles, are identified by comparing the two simulation results. Compared to theoretical or semi-empirical leakage and windage models, higher loss production and temperature rise are found especially in mid to rear stages. Unsteady effects for such differences are discussed.

Evaluation of Compressor Blading With Blade End Slots and Full-Span Slots in a Highly Loaded Compressor Cascade

2019 ◽  
Author(s):  
Yumeng Tang ◽  
Yangwei Liu ◽  
Lipeng Lu
Keyword(s):  
Incidence Angle ◽  
Three Dimensional ◽  
Main Flow ◽  
The Self ◽  
Flow Structures ◽  
Two Dimensional ◽  
Compressor Cascade ◽  
Aero Engine ◽  
Compressor Performance ◽  
Highly Loaded

Abstract High loading design is a permanent pursuit in the field of the modern compressors to reduce the size and weight of the aero-engine. Blading with slots is a potential way to improve compressor performance. An innovative double-slot scheme was proposed and validated to control corner separation in a highly loaded compressor cascade in our previous studies. To evaluate the three-dimensional (3D) performance of blading with slots, the current research compares the performance of blading with full-span slots to that with blade end slots. First, the two-dimensional (2D) configuration performance is evaluated both for the datum and slotted profiles. The slotted configuration could effectively supress separation, especially under positive incidence conditions where the separation of the datum profile is large. Thus, two 3D blading forms, the full-span slots and the blade end slots (covering 20% of the span from the endwall), are compared within. Results show that blading with full-span slots could effectively reduce the loss under positive incidence angles, while blading with blade end slots could effectively reduce the loss above an incidence angle of −4°. The loss for the end slotted blade is lower than that of the full-span slotted blade under most incidence angles (within the range of 4°). The additional mixing loss of the jet and the main flow are caused by the full-span slots at the mid-span regions where the flow remains attached for the unslotted geometry. Blading with slots alters the flow structures and reorganises the flow in the blade end regions. The self-adaptive jets from the slot outlet push the accumulated low-momentum flow downstream and restrain its migration toward the mid-span, such that the uniform main flow in the blade mid-span region is enhanced.

3D simulation of emulsion flow using the boundary element method on the heterogeneous computational systems

2012 ◽  
Vol 9 (1) ◽  
pp. 142-146
Author(s):  
O.A. Solnyshkina
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Problem Size ◽  
Low Reynolds Numbers ◽  
Infinite Domains ◽  
The Matrix ◽  
Computational Systems ◽  
Element Method

In this work the 3D dynamics of two immiscible liquids in unbounded domain at low Reynolds numbers is considered. The numerical method is based on the boundary element method, which is very efficient for simulation of the three-dimensional problems in infinite domains. To accelerate calculations and increase the problem size, a heterogeneous approach to parallelization of the computations on the central (CPU) and graphics (GPU) processors is applied. To accelerate the iterative solver (GMRES) and overcome the limitations associated with the size of the memory of the computation system, the software component of the matrix-vector product

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