NAM Application for Simulation of Unsteady Separation Flow around Airfoil with Spoiler

2014 ◽  
Vol 598 ◽  
pp. 156-159
Author(s):  
Vladimir A. Frolov ◽  
Ksenia V. Redkina ◽  
Liu He
Keyword(s):  
Complex Variable ◽  
Separated Flow ◽  
Vortex Sheet ◽  
Separation Flow ◽  
Time Step ◽  
Unsteady Separation ◽  
Numerical Analytical Method ◽  
Modeling Behavior ◽  
Separation Zones ◽  
Unsteady Separated Flow

A Numerical-Analytical Method (NAM) and Discrete Vortices Method (DVM) are developed for simulating unsteady separated flow around an airfoil with a spoiler. For flow separated at each sharp edge, such as the spoiler tips and the trailing edge of the airfoil, a vortex sheet is used to feed discrete vortices at each time step. The solution is determined under the assumption of fluid being ideal and incompressible. This paper develops modeling behavior of the vortices around the airfoil with the spoiler. The NAM based into the combination of the DVM and TFCV (Theory Function of Complex Variable) that gives to increase the accuracy of the calculation. In this paper the variation of the separation zones for the unsteady separated flow are shown.

Unsteady Mechanisms of Compressor Corner Separation Over a Range of Incidences Based on Hybrid LES/RANS

2013 ◽  
Author(s):  
Zhong-Nan Wang ◽  
Xin Yuan
Keyword(s):  
Separated Flow ◽  
Suction Side ◽  
Separated Flows ◽  
Resonance Structure ◽  
Separation Flow ◽  
Trailing Edge ◽  
Flow Physics ◽  
Unsteady Separation ◽  
Large Pressure ◽  
Corner Flows

The separation flow pattern in compressor corners is well known but its nature is not fully understood. In this paper, the numerical simulation based on hybrid LES/RANS was performed to improve our understanding about the unsteady separation structure and its dynamic mechanisms of compressor corner flows, subject to a range of incoming flow incidences. In the simulation, the attached boundary layer near the walls was modeled by RANS, while the large separated flows in the corner were resolved by LES. The simulation was carefully validated by the experimental data before flow physics investigation. The unsteady separation structures and its effects were then investigated step by step, from phenomena observation to mechanisms analysis. First, the overall separation behavior and its associated flow physics was visualized and analyzed. It was found that the unsteady separation structure was distinct from the steady view. Some additional vortex structures, normally smeared out in the steady averaging process, were crucial in the unsteady dynamic process. These small but critical vortices corresponded to large intermittency in the separation size and strength. As the incidences increased, the vortex structure became much more complex due to the enhanced interaction of these vortices. Second, the turbulence behavior was examined in the separated regions. Anisotropy and non-equilibrium of turbulence were found to be dominant in the separation region due to non-homogenous shear of the separated flow. It posed a big challenge for conventional RANS prediction. Finally, the unsteadiness of corner separated flows was fully analyzed over a range of incidences. It was found that the unsteadiness came from two sources: the suction side separation and the wake shedding. The unsteadiness increased with the incidences. The two unsteady sources interacted with each other at high incidences, which led to a big unsteady resonance structure near the blade trailing edge. The resonance was responsible for a large pressure variation, implying the enhanced noise generation near the blade trailing edge.

Numerical Study of Unsteady Flow Around Airfoil With Spoiler

1998 ◽  
Vol 65 (1) ◽  
pp. 164-170 ◽  
Author(s):  
Cheng Xu ◽  
W. W. H. Yeung
Keyword(s):  
Numerical Study ◽  
Piecewise Linear ◽  
Separated Flow ◽  
Vortex Sheet ◽  
Time Step ◽  
Discrete Vortex ◽  
Vortex Model ◽  
Bernoulli’S Equation ◽  
Pressure Distributions ◽  
Rapid Deployment

A discrete vortex model based on the panel method has been developed to simulate the two-dimensional unsteady separated flow generated by the rapid deployment of a spoiler on the upper surface of an airfoil. This method represents the boundary surfaces by distributing piecewise linear-vortex and constant source singularities on discrete panels. The wake of the spoiler and airfoil is represented by discrete vortices. At each sharp edge, a vortex sheet is used to feed discrete vortices at every time-step to form the downstream wake. The length and strength of each shed vortex sheet are determined by the continuity equation and a condition such that the flow, the net force, and the pressure difference across the vortex sheet are zero. The flow patterns behind the spoiler at different time-steps are presented. The pressure distributions on the airfoil based on the unsteady Bernoulli’s equation are compared, where possible, with the experimental results and other computational results. The adverse lift effects have been obtained, and similar effects have been measured in experiments.

Aerodynamic characteristics of an unsteady separated flow

1979 ◽  
Author(s):  
M. FRANCIS ◽  
J. KEESEE ◽  
J. LANG ◽  
G. SPARKS ◽  
G. SISSON
Keyword(s):  
Separated Flow ◽  
Aerodynamic Characteristics ◽  
Unsteady Separated Flow

Separated Flow Past a Slender Delta Wing at Incidence

1973 ◽  
Vol 24 (2) ◽  
pp. 120-128 ◽  
Author(s):  
J E Barsby
Keyword(s):  
Delta Wing ◽  
Separated Flow ◽  
Leading Edge ◽  
Vortex Sheet ◽  
Simultaneous Equations ◽  
Delta Wings ◽  
Nested Iteration ◽  
Finite Difference Technique ◽  
Flow Past ◽  
Vortex Systems

SummarySolutions to the problem of separated flow past slender delta wings for moderate values of a suitably defined incidence parameter have been calculated by Smith, using a vortex sheet model. By increasing the accuracy of the finite-difference technique, and by replacing Smith’s original nested iteration procedure, to solve the non-linear simultaneous equations that arise, by a Newton’s method, it is possible to extend the range of the incidence parameter over which solutions can be obtained. Furthermore for sufficiently small values of the incidence parameter, new and unexpected results in the form of vortex systems that originate inboard from the leading edge have been discovered. These new solutions are the only solutions, to the author’s knowledge, of a vortex sheet leaving a smooth surface.Interest has centred upon the shape of the finite vortex sheet, the position of the isolated vortex, and the lift, and variations of these quantities are shown as functions of the incidence parameter. Although no experimental evidence is available, comparisons are made with the simpler Brown and Michael model in which all the vorticity is assumed to be concentrated onto an isolated line vortex. Agreement between these two models becomes very close as the value of the incidence parameter is reduced.

A numerical investigation of the rolling-up of vortex sheets

1980 ◽  
Vol 373 (1752) ◽  
pp. 67-91 ◽  
Keyword(s):  
Numerical Integration ◽  
Numerical Investigation ◽  
Equations Of Motion ◽  
Additional Term ◽  
Vortex Sheet ◽  
Time Step ◽  
Vortex Sheets ◽  
Numerical Instabilities ◽  
Sinusoidal Disturbance ◽  
Induced Velocity

In this paper the development of a vortex sheet due to an initially sinusoidal disturbance is calculated. When determining the induced velocity in points of the vortex sheet, it can be represented by concentrated vortices but it is shown that it is analytically more correct to add an additional term that represents the effect of the immediate neighbourhood of the point considered. The equations of motion were integrated by a Runge-Kutta technique to exclude numerical instabilities. The time step was determined by the requirement that a quantity (Hamiltonian) that remains invariant as a result of the equations of motion, should not change more than a certain amount in the numerical integration of the equations of motion. One difficulty is that if a greater number of concentrated vortices are introduced to represent the vortex sheet, the effect of round-off errors becomes more important. The number of figures retained in the computations limits the number of concentrated vortices. Where the round-off errors have been kept sufficiently small, a process of rolling-up of vorticity clearly occurs. There is no point in pursuing the calculations much beyond this point, first because the representation of the vortex sheet by concentrated vortices becomes more and more inaccurate and secondly because viscosity will have the effect of transforming the rolled-up vortex sheet into a region of vorticity.

Numerical Analysis of Cavitation Inception and Desinence Behind Orifices

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
E. L. Amromin
Keyword(s):  
Experimental Data ◽  
Numerical Analysis ◽  
Separated Flow ◽  
Computational Procedure ◽  
Cavitation Number ◽  
Laminar Flows ◽  
Cavity Pressure ◽  
Cavitation Inception ◽  
Separation Zones

Abstract Experimental results and trends for cavitation inception and desinence behind orifices in microchannels are quite different from the data obtained during previous experiments in much larger facilities. The objective of this paper is to explain these differences via a numerical analysis. The employed computational procedure is divided into two parts. The first part is computation of an axisymmetric separated flow around the orifice. The second part is determination of characteristics of cavities appearing within separation zones. The provided analysis of the experimental data of other researchers pointed out two sources of the above-mentioned differences. First, for larger orifices, the cavities appear in the cores of drifting vortices. For such a situation, cavitation inception and desinence number increases with the inflow speed due to an impact of turbulence, but there is no such an increase for microbubbles with laminar flows. Second, because of the difficulty to measure the cavity pressure in microbubbles, cavitation number is usually defined with employment of the vapor pressure, and this leads to misinterpretation of the measurements and their trends.

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