Unsteady aerodynamic interaction of two annular blade rows of thin lightly loaded blades rotating one relative to the other in a subsonic flow

1991 ◽  
Vol 26 (3) ◽  
pp. 454-462 ◽  
Author(s):  
K. S. Reent
Keyword(s):  
Subsonic Flow ◽  
The Other ◽  
Unsteady Aerodynamic ◽  
Aerodynamic Interaction

scholarly journals Unsteady loads for coaxial rotors in forward flight computed using a vortex particle method

2018 ◽  
Vol 122 (1251) ◽  
pp. 693-714 ◽  
Author(s):  
J. Tan ◽  
Y. Sun ◽  
G. N. Barakos
Keyword(s):  
Flow Model ◽  
Particle Method ◽  
Reversed Flow ◽  
Aerodynamic Loads ◽  
Unsteady Aerodynamic ◽  
Vortex Particle Method ◽  
Coaxial Rotor ◽  
Aerodynamic Interaction ◽  
Coaxial Rotors ◽  
Vortex Particle

ABSTRACTRecent advances in coaxial rotor design have shown benefits of this configuration. Nevertheless, issues related to rotor-head drag, aerodynamic performance, wake interference, and vibration should also be considered. Simulating the unsteady aerodynamic loads for a coaxial rotor, including the aerodynamic interactions between rotors and rotor blades, is an essential part of analysing their vibration characteristics. In this article, an unsteady aerodynamic analysis based on a vortex particle method is presented. In this method, a reversed-flow model for the retreating side of the coaxial rotor is proposed based on an unsteady panel technique. To account for reversed flow, shedding a vortex from the leading edge is used rather than from the trailing edge. Moreover, vortex-blade aerodynamic interactions are accounted for. The model considers the unsteady pressure term induced on a blade by tip vortices of other blades, and thus accounts for the aerodynamic interaction between the rotors and its contribution to the unsteady airloads. Coupling the reversed-flow model and the vortex-blade aerodynamic interaction model with the viscous vortex-particle method is used to simulate the complex wake of the coaxial rotor. The unsteady aerodynamic loads on the X2 coaxial rotor are simulated in forward flight, and compared with the results of PRASADUM (Parallelized Rotorcraft Analysis for Simulation And Design, developed at the University of Maryland) and CFD/CSD computations with the OVERFLOW and the CREATE-AV Helios tools. The results of the present method agree with the results of the CFD/CSD method, and compare to it better than the PRASADUM solutions. Furthermore, the influence of the aerodynamic interaction between the coaxial rotors on the unsteady airloads, frequency, wake structure, induced flow, and force distributions are analysed. Additionally, the results are also compared against computations for a single-rotor case, simulated at similar conditions as the coaxial rotor. It is shown that the effect of tip vortex interaction plays a significant role in unsteady airloads of coaxial rotors at low speeds, while the rotor blade passing effect is obviously strengthened at high-speed.

Unsteady Aerodynamic Characteristics of Oscillating Cascade With Separation Bubble in High Subsonic Flow

2005 ◽  
Author(s):  
Toshinori Watanabe ◽  
Mizuho Aotsuka
Keyword(s):  
Subsonic Flow ◽  
Separation Bubble ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Influence Coefficient ◽  
Unsteady Aerodynamic ◽  
Key Factor ◽  
Influence Coefficient Method ◽  
Airfoil Blades ◽  
High Subsonic Flow

Unsteady aerodynamic characteristics of an oscillating cascade composed of DCA (Double Circular Arc airfoil) blades were studied both experimentally and numerically. The test cascade was operated in high subsonic flow fields with incidence angles up to 5 degrees. Above 3 degrees of the incidence, a separation bubble was produced at the leading edge. The principal concern of the present study was placed on the influence of the separated region on the vibration instability of the cascade blades. The experiment was conducted in a linear cascade wind tunnel in which seven DCA blades were equipped. The central one could be oscillated in a pitching mode. The influence coefficient method was adopted for the measurement, where the unsteady aerodynamic moments were measured on the central blade and neighboring ones. For the numerical analysis, a quasi 3-D N-S code with k–ε turbulence model was developed. The experimental and numerical results complemented each other to obtain detailed understanding of the unsteady aerodynamic behavior of the cascade. It was found that the separation bubble at the leading edge governed the vibration characteristics of blades through the oscillation of the separation bubble itself on the blade surfaces. From the results of parametric studies, the phase shift of the oscillation of the separation bubble was found to be a key factor for determining the unsteady aerodynamic characteristics of the oscillating blades.

Stochastic Analysis of a Nonlinear Forced Panel in Subsonic Flow With Random Pressure Fluctuations

2013 ◽  
Vol 80 (4) ◽  
Author(s):  
Peng Li ◽  
Yiren Yang ◽  
Wei Xu ◽  
Guo Chen
Keyword(s):  
Subsonic Flow ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
The Other ◽  
Moment Equations ◽  
Noise Spectral Density ◽  
Aerodynamic Pressure ◽  
Theoretical And Numerical Analysis ◽  
The Stability ◽  
Density Dynamic

The stochastic behavior of a two-dimensional nonlinear panel subjected to subsonic flow with random pressure fluctuations and an external forcing is studied in this paper. The total aerodynamic pressure is considered as the sum of two parts, one given by the random pressure fluctuations on the panel in the absence of any panel motion, and the other due to the panel motion itself. The random pressure fluctuations are idealized as a zero mean Brownian motion. Galerkin method is used to transform the governing partial differential equation to a series of ordinary differential equations. The closed moment equations are obtained by the Itô differential rule and Gauss truncation. The stability and complex responses of the moment equations are presented in theoretical and numerical analysis. Results show that a bifurcation of fixed points occurs and the bifurcation point is determined as functions of noise spectral density, dynamic pressure, and panel structure parameters; the chaotic response regions and periodic response regions appear alternately in parameter spaces, the periodic responses trajectories change rhythmically, and the route from periodic responses to chaos is via doubling-period bifurcation. The treatment suggested in this paper can also be extended for the other fluid-structure dynamic systems.

Comparison of the Unsteady Loads of an Airfoil in the Pitching and Plunging Motions

2006 ◽  
Author(s):  
M. Soltani ◽  
M. Seddighi ◽  
F. Rasi
Keyword(s):  
Subsonic Flow ◽  
Free Stream ◽  
Incident Angle ◽  
Oscillation Amplitude ◽  
Stream Velocity ◽  
Frequency Oscillation ◽  
Aerodynamic Loads ◽  
Unsteady Aerodynamic ◽  
Reduced Frequency ◽  
Series Of Experiments

A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of motion on the unsteady aerodynamic loads of the airfoil at pre-stall, near stall, and post stall conditions. Variations of the aerodynamic coefficients with equivalent angle of attack for both pitching and plunging motions showed strong sensitivity to the reduced frequency, oscillation amplitude, Reynolds number, and mean angles of attack.

Unsteady Aerodynamic Interactions in a Multistage Compressor

1987 ◽  
Vol 109 (3) ◽  
pp. 420-428 ◽  
Author(s):  
V. R. Capece ◽  
S. Fleeter
Keyword(s):  
Axial Flow ◽  
Unsteady Aerodynamic ◽  
Geometric Conditions ◽  
Forcing Function ◽  
Reduced Frequency ◽  
Aerodynamic Interaction ◽  
Blade Row ◽  
Unsteady Interaction ◽  
Multistage Compressor ◽  
Series Of Experiments

The fundamental flow physics of multistage blade row interactions is experimentally investigated, with unique data obtained which quantify the unsteady harmonic aerodynamic interaction phenomena. In particular, a series of experiments is performed in a three-stage axial flow research compressor over a range of operating and geometric conditions at high reduced frequency values. The multistage unsteady interaction effects of the following on each of the three vane rows are investigated: (1) the steady vane aerodynamic loading, (2) the waveform of the aerodynamic forcing function to each vane row, including both the chordwise and traverse gust components.

Experimental Investigation of Multistage Interaction Gust Aerodynamics

1989 ◽  
Vol 111 (4) ◽  
pp. 409-417 ◽  
Author(s):  
V. R. Capece ◽  
S. Fleeter
Keyword(s):  
Axial Flow ◽  
Unsteady Aerodynamics ◽  
Unique Data ◽  
Aerodynamic Loading ◽  
Unsteady Aerodynamic ◽  
Forcing Function ◽  
Reduced Frequency ◽  
Aerodynamic Interaction ◽  
Blade Row ◽  
Potential Interactions

The fundamental flow physics of multistage blade row interactions are experimentally investigated at realistic reduced frequency values. Unique data are obtained that describe the fundamental unsteady aerodynamic interaction phenomena on the stator vanes of a three-stage axial flow research compressor. In these experiments, the effect on vane row unsteady aerodynamics of the following are investigated and quantified: (1) steady vane aerodynamic loading; (2) aerodynamic forcing function waveform, including both the chordwise and transverse gust components; (3) solidity; (4) potential interactions; and (5) isolated airfoil steady flow separation.

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