Three-dimensional Separated Flow Topology

2013 ◽  
Keyword(s):  
Three Dimensional ◽  
Separated Flow ◽  
Flow Topology

scholarly journals Separated Flow Topology in Compressors

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
James V. Taylor
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Separated Flow ◽  
Cell Behavior ◽  
Blade Design ◽  
Flow Topology ◽  
Design Point ◽  
Topological Reasoning ◽  
Blade Row ◽  
Different Response

Abstract When a multistage high-speed compressor is operated away from its design point, extreme incidence is caused in some blade rows. This results in large, localized separations that are three dimensional in nature. In this paper, topological reasoning is used to describe the behavior of these three-dimensional separations. It is shown that two classes of separation exist: one in which the flow progresses from attached to separate in a smooth way and another where there is a discontinuity in the response of the flow topology. It is shown that the global structure of the flow depends on the type of topological response that occurs. When the response is discontinuous, nonaxisymmetric cells of separated blades are formed. When the response is smooth, the resultant separated flow is axisymmetric. The paper is split into two broad sections: The first section presents examples of the two different classes of topological response that can occur in a single blade row, and it also shows how an engineer can achieve a different response by altering the blade design. The second section covers the analysis of a multistage high-speed compressor. The compressor initially presents the discontinuous behavior with rotating cells of separations. It is then redesigned to reduce the severity of the cell behavior or remove it entirely.

Three-Dimensional and Rotational Aerodynamics on the NREL Phase VI Wind Turbine Blade

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Alvaro Gonzalez ◽  
Xabier Munduate
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Separated Flow ◽  
Leading Edge ◽  
Wind Turbine Blade ◽  
Trailing Edge ◽  
Rotating Blade ◽  
Nrel Phase Vi ◽  
Edge Separation

This work undertakes an aerodynamic analysis over the parked and the rotating NREL Phase VI wind turbine blade. The experimental sequences from NASA Ames wind tunnel selected for this study respond to the parked blade and the rotating configuration, both for the upwind, two-bladed wind turbine operating at nonyawed conditions. The objective is to bring some light into the nature of the flow field and especially the type of stall behavior observed when 2D aerofoil steady measurements are compared to the parked blade and the latter to the rotating one. From averaged pressure coefficients together with their standard deviation values, trailing and leading edge separated flow regions have been found, with the limitations of the repeatability of the flow encountered on the blade. Results for the parked blade show the progressive delay from tip to root of the trailing edge separation process, with respect to the 2D profile, and also reveal a local region of leading edge separated flow or bubble at the inner, 30% and 47% of the blade. For the rotating blade, results at inboard 30% and 47% stations show a dramatic suppression of the trailing edge separation, and the development of a leading edge separation structure connected with the extra lift.

Experiments on the stability of sinusoidal flow over a circular cylinder

2002 ◽  
Vol 457 ◽  
pp. 157-180 ◽  
Author(s):  
TURGUT SARPKAYA
Keyword(s):  
Stokes Flow ◽  
Coherent Structures ◽  
High Speed ◽  
Three Dimensional ◽  
Separated Flow ◽  
Circular Cylinders ◽  
Centrifugal Forces ◽  
Complex Interactions ◽  
Sinusoidal Flow ◽  
The Stability

The instabilities in a sinusoidally oscillating non-separated flow over smooth circular cylinders in the range of Keulegan–Carpenter numbers, K, from about 0.02 to 1 and Stokes numbers, β, from about 103 to 1.4 × 106 have been observed from inception to chaos using several high-speed imagers and laser-induced fluorescence. The instabilities ranged from small quasi-coherent structures, as in Stokes flow over a flat wall (Sarpkaya 1993), to three-dimensional spanwise perturbations because of the centrifugal forces induced by the curvature of the boundary layer (Taylor–Görtler instability). These gave rise to streamwise-oriented counter-rotating vortices or mushroom-shaped coherent structures as K approached the Kh values theoretically predicted by Hall (1984). Further increases in K for a given β led first to complex interactions between the coherent structures and then to chaotic motion. The mapping of the observations led to the delineation of four states of flow in the (K, β)-plane: stable, marginal, unstable, and chaotic.

Aeroelastic Stability of Lifting Surfaces in High-Density Fluids

1959 ◽  
Vol 3 (01) ◽  
pp. 10-21 ◽  
Author(s):  
Charles J. Henry ◽  
John Dugundji ◽  
Holt Ashley
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Separated Flow ◽  
High Density ◽  
Aeroelastic Stability ◽  
Free Surfaces ◽  
Elastic Systems ◽  
Static Instability ◽  
Theoretical Evidence ◽  
Lifting Surfaces

The large increases anticipated in speeds of vehicles towed or propelled underwater suggests a re-examination of the problem of stability of flexible lifting surfaces mounted thereon. Experimental and theoretical evidence is assembled which suggests that oscillatory aeroelastic instability (flutter) is very unlikely at the structural-to-fluid mass ratios typical of hydrodynamic operation. It is shown that static instability (divergence) is the more important practical problem but that its occurrence can be predicted with greater confidence. Flutter data obtained in high-density fluids are reviewed, and various sources of inaccuracy in their theoretical prediction are analyzed. The need is expressed for more precise means of analytically representing both dynamic-elastic systems and three-dimensional unsteady hydrodynamic loads. For a simple hydrofoil with single degrees of freedom in bending and torsion, the theoretical influence of several significant parameters on high-density flutter is calculated and discussed. Recommendations are made for refinements to existing techniques of analysis to include the presence of channel boundaries, free surfaces, cavitation or separated flow.

scholarly journals Numerical Study of Branched Turboprop Inlet Ducts Using a Multiple Block Grid Procedure

1991 ◽  
Author(s):  
Anil K. Tolpadi ◽  
Mark E. Braaten
Keyword(s):  
Numerical Solutions ◽  
Numerical Study ◽  
Three Dimensional ◽  
Separated Flow ◽  
Experimental Tests ◽  
Spherical Particles ◽  
Branch Duct ◽  
Pressure Losses ◽  
Overlapping Grids ◽  
Inlet Duct

An important requirement in the design of an inlet duct of a turboprop engine is the ability to provide foreign object damage protection. A possible method for providing this protection is to include a bypass branch duct as an integral part of the main inlet duct. This arrangement would divert ingested debris away from the engine through the bypass. However, such an arrangement could raise the possibility of separated flow in the inlet, which in turn can increase pressure losses if not properly accounted for during the design. A fully elliptic three-dimensional body-fitted computational fluid dynamics (CFD) code based on pressure correction techniques has been developed that has the capability of performing multiple block grid calculations compatible with present day turboshaft and turboprop branched inlet ducts. Calculations are iteratively performed between sets of overlapping grids with one grid representing the main duct and a second grid representing the branch duct. Both the grid generator and the flow solver have been suitably developed to achieve this capability. The code can handle multiple branches in the flow. Using the converged flow field from this code, another program was written to perform a particle trajectory analysis. Numerical solutions were obtained on a supercomputer for a typical branched duct for which experimental flow and pressure measurements were also made. The flow separation zones predicted by the calculations were found to be in good agreement with those observed in the experimental tests. The total pressure recovery factors measured in the experiments were also compared with those obtained numerically. Within the limits of the grid resolution and the turbulence model, the agreement was found to be fairly good. In order to simulate the path of debris entering the duct, the trajectories of spherical particles of different sizes introduced at the inlet were determined.

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