Inviscid-Viscous Coupled Solution for Unsteady Flows Through Vibrating Blades: Part 2—Computational Results

1993 ◽  
Vol 115 (1) ◽  
pp. 101-109 ◽  
Author(s):  
L. He ◽  
J. D. Denton
Keyword(s):  
Unsteady Flow ◽  
Transonic Flow ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Computational Results ◽  
Flow Conditions ◽  
Viscous Effects ◽  
Blade Flutter ◽  
Coupled Solution

A quasi-three-dimensional inviscid-viscous coupled approached has been developed for unsteady flows around oscillating blades, as described in Part 1. To validate this method, calculations for several steady and unsteady flow cases with strong inviscid-viscous interactions are performed, and the results are compared with the corresponding experiments. Calculated results for unsteady flows around a biconvex cascade and a fan tip section highlight the necessity of including viscous effects in predictions of turbomachinery blade flutter at transonic flow conditions.

Inviscid-Viscous Coupled Solution for Unsteady Flows Through Vibrating Blades: Part 2 — Computational Results

1991 ◽  
Author(s):  
L. He ◽  
J. D. Denton
Keyword(s):  
Unsteady Flow ◽  
Transonic Flow ◽  
Unsteady Flows ◽  
Computational Results ◽  
Flow Conditions ◽  
Viscous Effects ◽  
Blade Flutter ◽  
Coupled Solution

A quasi 3-D inviscid-viscous coupled approach has been developed for unsteady flows around oscillating blades, as described in Part 1. To validate this method, calculations for several steady and unsteady flow cases with strong inviscid-viscous interactions are performed, and the results are compared with the corresponding experiments. Calculated results for unsteady flows around a bi-convex cascade and a fan tip section highlight the necessity of including viscous effects in predictions of turbomachinery blade flutter at transonic flow conditions.

scholarly journals Investigation of the Unsteady Flow Behaviour on a Wind Turbine Using a BEM and a RANSE Method

2016 ◽  
Vol 2016 ◽  
pp. 1-12
Author(s):  
Israa Alesbe ◽  
Moustafa Abdel-Maksoud ◽  
Sattar Aljabair
Keyword(s):  
Unsteady Flow ◽  
Wind Turbine ◽  
Pressure Distribution ◽  
Three Dimensional ◽  
Panel Method ◽  
Flow Behaviour ◽  
Viscous Effects ◽  
Horizontal Axis Wind Turbine ◽  
Local Flow ◽  
Ranse Solver

Analyses of the unsteady flow behaviour of a 5 MW horizontal-axis wind turbine (HAWT) rotor (Case I) and a rotor with tower (Case II) are carried out using a panel method and a RANSE method. The panel method calculations are obtained by applying the in-house boundary element method (BEM) panMARE code, which is based on the potential flow theory. The BEM is a three-dimensional first-order panel method which can be used for investigating various steady and unsteady flow problems. Viscous flow simulations are carried out by using the RANSE solver ANSYS CFX 14.5. The results of Case I allow for the calculation of the global integral values of the torque and the thrust and include detailed information on the local flow field, such as the pressure distribution on the blade sections and the streamlines. The calculated pressure distribution by the BEM is compared with the corresponding values obtained by the RANSE solver. The tower geometry is considered in the simulation in Case II, so the unsteady forces due to the interaction between the tower and the rotor blades can be calculated. The application of viscous and inviscid flow methods to predict the forces on the HAWT allows for the evaluation of the viscous effects on the calculated HAWT flows.

Non-Equilibrium Relaxing Gas Flow Behind Three Dimensional Unsteady Curved Shock Wave

1980 ◽  
Vol 35 (11) ◽  
pp. 1166-1170
Author(s):  
V. D. Sharma ◽  
Radhe Shyam
Keyword(s):  
Shock Wave ◽  
Unsteady Flow ◽  
Gas Flow ◽  
Three Dimensional ◽  
Flow Conditions ◽  
Shock Surface ◽  
Flow Parameters ◽  
Upstream Flow ◽  
Relaxing Gas ◽  
Non Equilibrium

Abstract A shock wave is assumed to exist in a three-dimensional unsteady flow of a relaxing gas. The variation of flow parameters at any point behind the shock surface is determined in terms of the shock geometry and the upstream flow conditions. The expressions for the vorticity and the curvature of a streak line at the rear of the shock surface are also determined in terms of the known quantities.

scholarly journals A Linearized Euler Analysis of Unsteady Transonic Flows in Turbomachinery

1993 ◽  
Author(s):  
Kenneth C. Hall ◽  
William S. Clark ◽  
Christopher B. Lorence
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Computational Method ◽  
Shock Capturing ◽  
Flow Conditions ◽  
Mean Flow ◽  
Transonic Flows ◽  
Linearized Euler Equations ◽  
Volume Equations

A computational method for efficiently predicting unsteady transonic flows in two- and three-dimensional cascades is presented. The unsteady flow is modelled using a linearized Euler analysis whereby the unsteady flow field is decomposed into a nonlinear mean flow plus a linear harmonically varying unsteady flow. The equations that govern the perturbation flow, the linearized Euler equations, are linear variable coefficient equations. For transonic flows containing shocks, shock capturing is used to model the shock impulse (the unsteady load due to the harmonic motion of the shock). A conservative Lax-Wendroff scheme is used to obtain a set of linearized finite volume equations that describe the harmonic small disturbance behavior of the flow. Conditions under which such a discretization will correctly predict the shock impulse are investigated. Computational results are presented that demonstrate the accuracy and efficiency of the present method as well as the essential role of unsteady shock impulse loads on the flutter stability of fans.

Utilizing Bi-Stability to Improve the Performance of Wake-Galloping Energy Harvesters in Unsteady Flow

2016 ◽  
Author(s):  
Ali H. Alhadidi ◽  
Mohammed F. Daqaq ◽  
Hamid Abderrahmane
Keyword(s):  
Wind Tunnel ◽  
Unsteady Flow ◽  
Output Power ◽  
Bluff Body ◽  
Unsteady Flows ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Restoring Force ◽  
Energy Harvesters ◽  
Piezoelectric Cantilever

This paper investigates exploiting a bi-stable restoring force to enhance the transduction of wake-galloping energy harvesters in unsteady flows. To that end, a harvester consisting of a piezoelectric cantilever beam augmented with a square-sectioned bluff body at the free end is considered. Two repulsive magnets located at the tip of the beam are used to introduce the bi-stable restoring force. Unsteadiness is generated in a wind tunnel using static-grid structures located in the upstream of the bluff body. Three different mesh screens with square bars are designed with different bar and mesh widths to control the Reynolds numbers and associated unsteadiness. A series of wind tunnel tests are then used to experimentally investigate the response of the harvester with and without the tip magnets. Results demonstrate that the bi-stable restoring force can be used to improve the output power of the harvester under unsteady flow conditions.

M. J. Hartmann Memorial Session Paper: A Review of Research on Turbomachinery at MIT Traceable to Support From Mel Hartmann

1994 ◽  
Vol 116 (4) ◽  
pp. 570-580 ◽  
Author(s):  
J. L. Kerrebrock
Keyword(s):  
Transonic Flow ◽  
Flux Distribution ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Faculty Members ◽  
Heat Flux Distribution ◽  
Blow Down ◽  
Session Paper ◽  
Support Of Research

Research conducted at MIT since 1968 stemming from early initiatives on the Blow-down Compressor Experiment and on transonic three-dimensional CFD is reviewed from the viewpoint of the consequences of enlightened support of research by exceptionally capable leaders of government research. Among the consequences in this case are development of detailed understanding of the unsteady flows in transonic compressors and their contribution to losses, and the ability to compute the three-dimensional transonic flow in such machines. Analogous results for turbines include the ability to measure and compute the unsteady heat flux distribution on turbine blades and vanes as well as the flow field. In addition to these research results, the programs traceable to Mel Hartmann’s early support have produced more than seven faculty members who continue to teach and conduct research in aircraft propulsion and closely related fields, and a corresponding number of students.

Calculation of Three-Dimensional Unsteady Flows in Turbomachinery Using the Linearized Harmonic Euler Equations

1993 ◽  
Vol 115 (4) ◽  
pp. 800-809 ◽  
Author(s):  
K. C. Hall ◽  
C. B. Lorence
Keyword(s):  
Unsteady Flow ◽  
Euler Equations ◽  
Small Perturbation ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Large Error ◽  
Surface Boundary ◽  
Mean Flow ◽  
Airfoil Surface ◽  
Acceleration Techniques

An efficient three-dimensional Euler analysis of unsteady flows in turbomachinery is presented. The unsteady flow is modeled as the sum of a steady or mean flow field plus a harmonically varying small perturbation flow. The linearized Euler equations, which describe the small perturbation unsteady flow, are found to be linear, variable coefficient differential equations whose coefficients depend on the mean flow. A pseudo-time time-marching finite-volume Lax-Wendroff scheme is used to discretize and solve the linearized equations for the unknown perturbation flow quantities. Local time stepping and multiple-grid acceleration techniques are used to speed convergence. For unsteady flow problems involving blade motion, a harmonically deforming computational grid, which conforms to the motion of the vibrating blades, is used to eliminate large error-producing extrapolation terms that would otherwise appear in the airfoil surface boundary conditions and in the evaluation of the unsteady surface pressure. Results are presented for both linear and annular cascade geometries, and for the latter, both rotating and nonrotating blade rows.

scholarly journals Validation of a Nonlinear Unsteady Aerodynamic Simulator for Vibrating Blade Rows

1996 ◽  
Author(s):  
Timothy C. Ayer ◽  
Joseph M. Verdon
Keyword(s):  
Unsteady Flows ◽  
Harmonic Component ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Accurate Analysis ◽  
Transonic Flows ◽  
Unsteady Aerodynamic ◽  
Unsteady Surface Pressure ◽  
Blade Flutter ◽  
Displacement Effects

A time-accurate Euler/Navier-Stokes analysis is applied to predict unsteady subsonic and transonic flows through a vibrating cascade. The intent is to validate this nonlinear analysis along with an existing linearized inviscid analysis via result comparisons for unsteady flows that are representative of those associated with blade flutter. The time-accurate analysis has also been applied to determine the relative importance of nonlinear and viscous effects on blade response. The subsonic results reveal a close agreement between inviscid and viscous unsteady blade loadings. Also, the unsteady surface pressure responses are essentially linear, and predicted quite accurately using a linearized inviscid analysis. For unsteady transonic flows, shocks and their motions cause significant nonlinear contributions to the local unsteady response. Viscous displacement effects tend to diminish shock strength and impulsive unsteady shock loads. For both subsonic and transonic flows, the energy transfer between the fluid and the structure is essentially captured by the first-harmonic component of the nonlinear unsteady solutions, but in transonic flows, the nonlinear first-harmonic and the linearized inviscid responses differ significantly in the vicinity of shocks.

Three-Dimensional Unsteady Flow for an Oscillating Turbine Blade and the Influence of Tip Leakage

1998 ◽  
Vol 122 (1) ◽  
pp. 93-101 ◽  
Author(s):  
D. L. Bell ◽  
L. He
Keyword(s):  
Unsteady Flow ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Tip Clearance ◽  
Computational Results ◽  
Blade Loading ◽  
Tip Leakage ◽  
Unsteady Pressure ◽  
Reduced Frequency

The results of two investigations, concerning the aerodynamic response of a turbine blade oscillating in a three-dimensional bending mode, are presented in this paper. The first is an experimental and computational study, designed to produce detailed three-dimensional test cases for aeroelastic applications and examine the ability of a three-dimensional time-marching Euler method to predict the relevant unsteady aerodynamics. Extensive blade surface unsteady pressure measurements were obtained over a range of reduced frequency from a test facility with clearly defined boundary conditions (Bell and He, 1997, ASME Paper No. 97-GT-105). The test data indicate a significant three-dimensional effect, whereby the amplitude of the unsteady pressure response at different spanwise locations is largely insensitive to the local bending amplitude. The computational results, which are the first to be supported by detailed three-dimensional test data, demonstrate the ability of the inviscid method to capture the three-dimensional behavior exhibited by the experimental measurements and a good level of quantitative agreement is achieved throughout the range of reduced frequency. Additional computational solutions, obtained through application of the strip methodology, reveal inadequacies in the conventional quasi-three-dimensional approach to the prediction of oscillating blade flows. The issue of linearity is also considered, and both experimental and computational results indicate a linear behavior of the unsteady aerodynamics. The second, an experimental investigation, addresses the influence of tip leakage upon the unsteady aerodynamic response of an oscillating turbine blade. Results are provided for three settings of tip clearance. The steady flow measurements show marked increases in the size and strength of the tip leakage vortex for the larger settings of tip clearance and deviations are present in the blade loading toward the tip section. The changes in tip clearance also caused distinct trends in the amplitude of the unsteady pressure at 90 percent span, which are observed to correspond with localized regions where the tip leakage flow had a discernible impact on the steady flow blade loading characteristic. The existence of these trends in the unsteady pressure response warrants further investigation into the influence of tip leakage on the local unsteady flow and aerodynamic damping. [S0889-504X(00)01101-6]

A Nonlinear Numerical Simulator for Three-Dimensional Flows Through Vibrating Blade Rows

1998 ◽  
Author(s):  
H. Andrew Chuang ◽  
Joseph M. Verdon
Keyword(s):  
Three Dimensional ◽  
Unsteady Flows ◽  
Operating Characteristics ◽  
Blade Vibration ◽  
Subsonic Flows ◽  
Transonic Flows ◽  
Multi Stage ◽  
Blade Row ◽  
Blade Flutter ◽  
Numerical Simulator

The three-dimensional, multi-stage, unsteady, turbomachinery analysis, TURBO, has been extended to predict the aeroelastic and aeroacoustic response behaviors of a blade row operating within a cylindrical annular duct. In particular, a blade vibration capability has been incorporated so that the TURBO analysis can be applied over a solution domain that deforms with a vibratory blade motion. Also, unsteady far-field conditions have been implemented to render the computational inlet and exit boundaries transparent to outgoing unsteady disturbances and to allow for the prescription of incoming aerodynamic excitations. The modified TURBO analysis has been applied to predict unsteady subsonic and transonic flows. The intent is to partially validate this nonlinear analysis for blade flutter applications via numerical results for benchmark unsteady flows, and to demonstrate this analysis for a realistic fan rotor. For these purposes, we have considered unsteady subsonic flows through a 3D version of the 10th Standard Cascade and unsteady transonic flows through the first stage rotor of the NASA Lewis, Rotor 67 fan. Some general correlations between aeromechanical stabilities and fan operating characteristics will be presented.

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