Investigation of Flutter Mechanisms of a Contra-Rotating Open Rotor

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Sina C. Stapelfeldt ◽  
Anthony B. Parry ◽  
Mehdi Vahdati
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Suction Side ◽  
Numerical Approach ◽  
Torsional Mode ◽  
Nodal Diameter ◽  
Aerodynamic Damping ◽  
Pressure Profiles ◽  
Open Rotor ◽  
State Mixing

The growing pressure to reduce fuel consumption and cut emissions has triggered renewed interest in contra-rotating open rotor (CROR) technologies. One of their potential issues is self-excited or forced vibration of the unducted, light-weight, highly swept blades. This paper presents a numerical study into the flutter behavior of a CROR rig at take-off conditions. The study presented in this paper aimed to validate the numerical approach and provide insights into the flutter mechanisms of the open rotor under investigation. For the initial validation, pressure profiles and thrust coefficients from steady-state mixing plane calculations were compared against rig measurements. A full domain unsteady analysis predicted front rotor instability at low advance ratios. Flutter occurred in the first torsional mode in 0 and 1 nodal diameter (ND) which agreed with experimental observations. Subsequent unsteady computations focused on the isolated front rotor and first torsional mode. The flow field and aerodynamic damping over a range of advance ratios were studied. It was found that minimum aerodynamic damping occurred at low advance ratios when the flow was highly three-dimensional on the suction side. A correlation between the quasi-steady loading on the blade and aeroelastic stability was made and related to the numerical results. The effects of variations in frequency were then investigated by linking local aerodynamic damping to the unsteady pressure on the blade surface.

Investigation of Flutter Mechanisms of a Contra-Rotating Open Rotor

2015 ◽  
Author(s):  
Sina C. Stapelfeldt ◽  
Mehdi Vahdati ◽  
Anthony B. Parry
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Suction Side ◽  
Numerical Approach ◽  
Torsional Mode ◽  
Aerodynamic Damping ◽  
Initial Validation ◽  
Pressure Profiles ◽  
Open Rotor ◽  
State Mixing

The growing pressure to reduce fuel consumption and cut emissions has triggered renewed interest in contra-rotating open rotor technologies. One of their potential issues is self-excited or forced vibration of the unducted, light-weight, highly swept blades. This paper presents a numerical study into the flutter behaviour of a contra-rotating open rotor rig at take-off conditions. The study presented in this paper aimed to validate the numerical approach and provide insights into the flutter mechanisms of the open rotor under investigation. For the initial validation, pressure profiles and thrust coefficients from steady state mixing plane calculations were compared against rig measurements. A full domain unsteady analysis predicted front rotor instability at low advance ratios. Flutter occured in the first torsional mode in 0ND and 1ND which agreed with experimental observations. Subsequent unsteady computations focussed on the isolated front rotor and first torsional mode. The flow field and aerodynamic damping over a range of advance ratios was studied. It was found that minimum aerodynamic damping occured at low advance ratios when the flow was highly three-dimensional on the suction side. A correlation between the quasi-steady loading on the blade and aeroelastic stability was made and related to the numerical results. The effects of variations in frequency were then investigated by linking local aerodynamic damping to the unsteady pressure on the blade surface.

Thermal jet drilling of granite rock: a numerical 3D finite-element study

2021 ◽  
Vol 379 (2196) ◽  
pp. 20200128
Author(s):  
Timo Saksala ◽  
Reijo Kouhia ◽  
Ahmad Mardoukhi ◽  
Mikko Hokka
Keyword(s):  
Finite Elements ◽  
Numerical Study ◽  
Thermal Flux ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Mass Scaling ◽  
Granite Rock ◽  
Fracture Dynamics ◽  
Rock Heterogeneity ◽  
Thermal Drilling

This paper presents a numerical study on thermal jet drilling of granite rock that is based on a thermal spallation phenomenon. For this end, a numerical method based on finite elements and a damage–viscoplasticity model are developed for solving the underlying coupled thermo-mechanical problem. An explicit time-stepping scheme is applied in solving the global problem, which in the present case is amenable to extreme mass scaling. Rock heterogeneity is accounted for as random clusters of finite elements representing rock constituent minerals. The numerical approach is validated based on experiments on thermal shock weakening effect of granite in a dynamic Brazilian disc test. The validated model is applied in three-dimensional simulations of thermal jet drilling with a short duration (0.2 s) and high intensity (approx. 3 MW m −2 ) thermal flux. The present numerical approach predicts the spalling as highly (tensile) damaged rock. Finally, it was shown that thermal drilling exploiting heating-forced cooling cycles is a viable method when drilling in hot rock mass. This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.

On the Role of Leading-Edge Bumps in the Control of Stall Onset in Axial Fan Blades

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Alessandro Corsini ◽  
Giovanni Delibra ◽  
Anthony G. Sheard
Keyword(s):  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Axial Fan ◽  
Early Recovery ◽  
Viscosity Models ◽  
Flow Mechanisms ◽  
The Impact

Taking a lead from the humpback whale flukes, characterized by a series of bumps that result in a sinusoidal-like leading edge, this paper reports on a three-dimensional numerical study of sinusoidal leading edges on cambered airfoil profiles. The turbulent flow around the cambered airfoil with the sinusoidal leading edge was computed at different angles of attack with the open source solver OpenFOAM, using two different eddy viscosity models integrated to the wall. The reported research focused on the effects of the modified leading edge in terms of lift-to-drag performance and the influence of camber on such parameters. For these reasons a comparison with a symmetric airfoil is provided. The research was primarily concerned with the elucidation of the fluid flow mechanisms induced by the bumps and the impact of those mechanisms on airfoil performance, on both symmetric and cambered profiles. The bumps on the leading edge influenced the aerodynamic performance of the airfoil, and the lift curves were found to feature an early recovery in post-stall for the symmetric profile with an additional gain in lift for the cambered profile. The bumps drove the fluid dynamic on the suction side of the airfoil, which in turn resulted in the capability to control the separation at the trailing edge in coincidence with the peak of the sinusoid at the leading edge.

A numerical study of three-dimensional turbulent channel flow at large Reynolds numbers

1970 ◽  
Vol 41 (2) ◽  
pp. 453-480 ◽  
Author(s):  
James W. Deardorff
Keyword(s):  
Scale Effects ◽  
Numerical Study ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Numerical Approach ◽  
Uniform Grid ◽  
Turbulence Energy ◽  
Vertical Diffusion

The three-dimensional, primitive equations of motion have been integrated numerically in time for the case of turbulent, plane Poiseuille flow at very large Reynolds numbers. A total of 6720 uniform grid intervals were used, with sub-grid scale effects simulated with eddy coefficients proportional to the local velocity deformation. The agreement of calculated statistics against those measured by Laufer ranges from good to marginal. The eddy shapes are examined, and only theu-component, longitudinal eddies are found to be elongated in the downstream direction. However, the lateralveddies have distinct downstream tilts. The turbulence energy balance is examined, including the separate effects of vertical diffusion of pressure and local kinetic energy.It is concluded that the numerical approach to the problem of turbulence at large Reynolds numbers is already profitable, with increased accuracy to be expected with modest increase of numerical resolution.

A Navier–Stokes Analysis of Airfoils in Oscillating Transonic Cascades for the Prediction of Aerodynamic Damping

1997 ◽  
Vol 119 (1) ◽  
pp. 77-84 ◽  
Author(s):  
R. S. Abhari ◽  
M. Giles
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Outer Region ◽  
Navier Stokes ◽  
Compressor Cascade ◽  
Time Step ◽  
Aerodynamic Damping ◽  
Transonic Compressor ◽  
Standard Configuration ◽  
The Impact

An unsteady, compressible, two-dimensional, thin shear layer Navier–Stokes solver is modified to predict the motion-dependent unsteady flow around oscillating airfoils in a cascade. A quasi-three-dimensional formulations is used to account for the stream-wise variation of streamtube height. The code uses Ni’s Lax–Wendroff algorithm in the outer region, an implicit ADI method in the inner region, conservative coupling at the interface, and the Baldwin–Lomax turbulence model. The computational mesh consists of an O-grid around each blade plus an unstructured outer grid of quadrilateral or triangular cells. The unstructured computational grid was adapted to the flow to better resolve shocks and wakes. Motion of each airfoil was simulated at each time step by stretching and compressing the mesh within the O-grid. This imposed motion consists of harmonic solid body translation in two directions and rotation, combined with the correct interblade phase angles. The validity of the code is illustrated by comparing its predictions to a number of test cases, including an axially oscillating flat plate in laminar flow, the Aeroelasticity of Turbomachines Symposium Fourth Standard Configuration (a transonic turbine cascade), and the Seventh Standard Configuration (a transonic compressor cascade). The overall comparison between the predictions and the test data is reasonably good. A numerical study on a generic transonic compressor rotor was performed in which the impact of varying the amplitude of the airfoil oscillation on the normalized predicted magnitude and phase of the unsteady pressure around the airfoil was studied. It was observed that for this transonic compressor, the nondimensional aerodynamic damping was influenced by the amplitude of the oscillation.

Numerical Study of Vortices and Their Interactions in the Passage of Rotor Blade With Tip Gap

2019 ◽  
Author(s):  
Sachin Singh Rawat ◽  
B. V. S. S. S. Prasad
Keyword(s):  
Turbulence Model ◽  
Numerical Study ◽  
Flow Direction ◽  
Three Dimensional ◽  
Suction Side ◽  
Leakage Flow ◽  
Angle Distribution ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage

Abstract A detailed three-dimensional steady-state numerical investigation using ANSYS CFX-18.2 on a high-pressure turbine blade with linear cascade is done for tip leakage flow of an axial gas turbine. Stationary casing with a fixed blade having tip gap is considered for the present study. There is leakage flow from the pressure side to the suction side of the blade which consecutively rolls up in the passage and forms the tip leakage vortex. The formation of vortices and their interaction with each other inside the passage is complex which makes experimental investigation difficult. The effect of tip gap size, off-design incidence angles, outlet Mach number, pitch size and flow path (stagger angle) are several parameters considered during the present study. The strength of tip leakage vortex and the vortex formed inside the gap is maximum. The losses are compared in terms of total pressure loss coefficient. The deviation of the flow direction is measured in terms of yaw angle distribution. Among various turbulence model available in CFX 18.2 the BSL k-ω turbulence model shows the most reliable results with experimental data. The results are compared with the base model without the tip gap. This investigation incites a better design of the blade tip with a precise reduction in losses.

Experimental and Numerical Study of a Subsonic Aspirated Cascade

2012 ◽  
Author(s):  
Antoine Godard ◽  
François Bario ◽  
Stéphane Burguburu ◽  
Francis Lebœuf
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Numerical Study ◽  
Design Method ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Design Feature ◽  
Suction Side ◽  
Compressor Blades ◽  
Pressure Losses

This paper presents the validation of a design method for aspirated compressor blades, combining a passive separation control by blade shaping with an active flow control by aspiration. In a first part, a linear aspirated cascade designed according to this method was built and tested at low speed, without and with aspiration. The latter was only applied on the suction surfaces of the blades. Particle Image Velocimetry measurements performed at mid-span of the cascade, in the central passage, showed a complete reattachment of the separated boundary layer on the suction side of the blade. A flow deflection of approximately 65 degrees was achieved requiring an aspirated mass flow rate of 3.3%. However, boundary layer reattachment is effective in a zone centered at mid-span covering 30% of blade span. Flow visualization revealed large corner separation in the presence of aspiration. This is due to the re-establishment of strong pressure gradient on sidewalls of the cascade. No flow control was applied on these zones for optical access purpose. These secondary-flow regions reduced the diffusion occurring within the cascade by nearly 60% in comparison with the design intent. They also increased the expected level of total pressure losses measured by wake traverses downstream of the cascade. In a second part, numerical simulations of the aforementioned experiment were carried out to help the understanding of the experimental results. The simulations were able to reproduce correctly the characteristic flow features, without and with aspiration, observed and measured during the experiment. Thus, they confirmed the potential of this design method developed for aspirated compressor blades, as well as CFD capabilities to simulate the influence of technological effects like suction slots. A uniform and a non-uniform aspiration distribution along the blade span direction were considered during simulations. Suction distribution was found to have a significant impact on the control by aspiration. This design feature, in addition to flow control on endwalls, has to be taken into account in the three-dimensional design of highly loaded aspirated compressor blades.

scholarly journals Numerical study of single bubble mobility in triangular and deltoid microchannels using the boundary element method

2021 ◽  
Vol 2057 (1) ◽  
pp. 012042
Author(s):  
A Z Bulatova ◽  
O A Solnyshkina ◽  
N B Fatkullina
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Complex Geometry ◽  
Numerical Study ◽  
Center Of Mass ◽  
Three Dimensional ◽  
Numerical Approach ◽  
Variable Pressure ◽  
Bubbly Liquid ◽  
Element Method

Abstract The study of bubbly liquid dynamics in microchannels of unconventional shapes is of great importance for different fields of science and industry. This work investigates the dynamics of the incompressible single bubbles in the slow periodic flow of viscous liquid in a triangular channel with a variable pressure gradient. The numerical approach used in this research is based on the boundary element method (BEM). This method is widely used for solving three-dimensional problems and problems in areas with complex geometry. The influence of the bubble’s initial position relative to the channel centerline on the bubble deformation, the relative velocity of the bubble, and its center of mass displacement in the channel are considered.

Numerical Study of Large Diameter Butterfly Valve on Flow Characteristics

2011 ◽  
Vol 236-238 ◽  
pp. 1653-1657 ◽  
Author(s):  
Xiao Dong Wang ◽  
Jing Liang Dong ◽  
Tian Wang
Keyword(s):  
Pressure Drop ◽  
Flow Resistance ◽  
Numerical Study ◽  
Large Diameter ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Numerical Approach ◽  
Resistance Coefficient ◽  
Butterfly Valve ◽  
Dimensional Simulation

A numerical approach was used to investigate the flow characteristics around a butterfly valve with the diameter of 2108 mm by the commercial computational fluid dynamics (CFD) code FLUENT6.3. The simulation was carried out to predict flow field structure, flow resistance coefficient, hydrodynamics torque and so on, when the large diameter butterfly valve operated at various opening degrees. The three-dimensional simulation results shown that there are vortexes presented near valve back region as the opening degree smaller than 40 degree; the flow resistance coefficient reduces rapidly with the increasing of opening degree and the resistance coefficient is quite small as the angle larger than 50 degree; the hydrodynamic torque reduces with the increasing of opening degree and the hydrodynamic torque is smaller than 20% of maximum torque; the torque ratio and the pressure drop ratio are reduce with the increasing of opening degree, the pressure drop ratio reduces rapidly as the opening degree is smaller than 50 degree.

Numerical Study of Instability Mechanisms Leading to Transition in Separation Bubbles

2006 ◽  
Author(s):  
B. R. McAuliffe ◽  
M. I. Yaras
Keyword(s):  
Numerical Simulation ◽  
Numerical Study ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Suction Side ◽  
Inertial Subrange ◽  
Momentum Exchange ◽  
Instability Growth ◽  
Tollmien Schlichting

In this paper, transition in a separation bubble is examined through numerical simulation. The flow Reynolds number and streamwise pressure distribution are typical of the conditions encountered on the suction side of low-pressure turbine blades of gas-turbine engines. The spatial and temporal resolutions utilized in the present computations correspond to a coarse direct numerical simulation, wherein the majority of turbulence scales, including the inertial subrange, are adequately resolved. The accuracy of the simulation results is demonstrated through favorable comparisons with experimental data corresponding to the same flow conditions. The results of the simulation show linear Tollmien-Schlichting (T-S) instability growth downstream of the point of separation, leading to the roll-up of spanwise vorticity into disctete vortical structures, characteristic of Kelvin-Helmholtz (K-H) instability growth. The extent of cross-stream momentum exchange associated with packets of amplified T-S waves is examined, along with details of the time-periodic breakdown into turbulence occurring upon the development of the K-H instability. Reynolds-averaged properties of the separation bubble are presented, and provide evidence of the strong three-dimensional nature of the reattachment process.

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