Influence of Acoustic Blockage on Flutter Instability in a Transonic Nozzle

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Quentin Rendu ◽  
Yannick Rozenberg ◽  
Stéphane Aubert ◽  
Pascal Ferrand
Keyword(s):  
Active Control ◽  
Separated Flow ◽  
Compressor Blade ◽  
Navier Stokes ◽  
Pressure Waves ◽  
Aeroelastic Stability ◽  
Design And Optimization ◽  
Flutter Instability ◽  
Unstable Configuration ◽  
Low Amplitude

In order to predict oscillating loads on a structure, time-linearized methods are fast enough to be routinely used in design and optimization steps of a turbomachine stage. In this work, frequency-domain time-linearized Navier–Stokes computations are proposed to predict the unsteady separated flow generated by an oscillating bump in a transonic nozzle. The influence of regressive pressure waves on the aeroelastic stability is investigated. This case is representative of flutter of a compressor blade submitted to downstream stator potential effects. The influence of frequency is first investigated on a generic oscillating bump to identify the most unstable configuration. Introducing backward traveling pressure waves, it is then showed that aeroelastic stability of the system depends on the phase shift between the wave's source and the bump motion. Finally, feasibility of active control through backward traveling pressure waves is evaluated. The results show a high stabilizing effect even for low amplitude, opening new perspectives for the active control of choke flutter.

Investigation of Shock-Wave/Boundary-Layer Interaction on Aeroelastic Stability: Towards Active Control

2016 ◽  
Author(s):  
Quentin Rendu ◽  
Yannick Rozenberg ◽  
Stéphane Aubert ◽  
Pascal Ferrand
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Pressure Fluctuations ◽  
Strong Shock ◽  
Separated Flow ◽  
Navier Stokes ◽  
Pressure Waves ◽  
Aeroelastic Stability ◽  
Design And Optimization ◽  
Boundary Layer Interaction

In order to predict oscillating loads on a structure, time-linearized methods are fast enough to be routinely used in design and optimization steps of a turbomachine stage. In this work, frequency-domain time-linearized Navier-Stokes computations are proposed to predict the unsteady separated flow generated by an oscillating bump in a transonic nozzle. We also investigate the interaction of backward traveling pressure waves and moving surface on the unsteady behavior of a strong shock-wave with separated boundary-layer. This case is representative of transonic stall flutter of a compressor blade submitted to downstream stator potential effects. The influence of frequency is first investigated on a generic oscillating bump to identify the most unstable configuration. Introducing back pressure fluctuations, we then show that the aeroelastic stability of the system depends on the phase-shift between the fluctuations and the bump motion. Finally, we propose to actively control the instability by generating backward traveling pressure waves at prescribed amplitude, frequency and phase.

scholarly journals Numerical analysis of high-lift configurations with oscillating flaps

2021 ◽  
Author(s):  
Johannes Ruhland ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Separated Flow ◽  
Navier Stokes ◽  
Rotational Axis ◽  
High Lift ◽  
Hinge Point ◽  
Reduced Frequency ◽  
Flap Deflection ◽  
The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

Computational Fluid Dynamic Applications for Jet Propulsion System Integration

1991 ◽  
Vol 113 (1) ◽  
pp. 40-50 ◽  
Author(s):  
R. H. Tindell
Keyword(s):  
System Integration ◽  
Fluid Dynamic ◽  
Low Cost ◽  
Separated Flow ◽  
Propulsion System ◽  
Navier Stokes ◽  
Aerospace Vehicles ◽  
Design Engineers ◽  
Flow Phenomena ◽  
The Impact

The impact of computational fluid dynamics (CFD) methods on the development of advanced aerospace vehicles is growing stronger year by year. Design engineers are now becoming familiar with CFD tools and are developing productive methods and techniques for their applications. This paper presents and discusses applications of CFD methods used at Grumman to design and predict the performance of propulsion system elements such as inlets and nozzles. The paper demonstrates techniques for applying various CFD codes and shows several interesting and unique results. A novel application of a supersonic Euler analysis of an inlet approach flow field, to clarify a wind tunnel-to-flight data conflict, is presented. In another example, calculations and measurements of low-speed inlet performance at angle of attack are compared. This is highlighted by employing a simplistic and low-cost computational model. More complex inlet flow phenomena at high angles of attack, calculated using an approach that combines a panel method with a Navier-Stokes (N-S) code, is also reviewed. The inlet fluid mechanics picture is rounded out by describing an N-S calculation and a comparison with test data of an offset diffuser having massively separated flow on one wall. Finally, the propulsion integration picture is completed by a discussion of the results of nozzle-afterbody calculations, using both a complete aircraft simulation in a N-S code, and a more economical calculation using an equivalent body of revolution technique.

Detached-Eddy Simulations Over a Simplified Landing Gear

2002 ◽  
Vol 124 (2) ◽  
pp. 413-423 ◽  
Author(s):  
L. S. Hedges ◽  
A. K. Travin ◽  
P. R. Spalart
Keyword(s):  
Stokes Equations ◽  
Separated Flow ◽  
Flow Fields ◽  
Equation Model ◽  
Landing Gear ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Instantaneous Flow ◽  
Eddy Simulation

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.

Numerical Investigation of Blade Flutter at or Near Stall in Axial Flow Turbomachines

2001 ◽  
Author(s):  
Wolfgang Höhn
Keyword(s):  
Viscous Flow ◽  
Stokes Equations ◽  
Separated Flow ◽  
Parallel Computer ◽  
Navier Stokes ◽  
Computational Domain ◽  
Compressor Cascade ◽  
Governing Equations ◽  
Navier Stokes Equations ◽  
Blade Flutter

During the design of the compressor and turbine stages of today’s aeroengines, aerodynamically induced vibrations become increasingly important since higher blade load and better efficiency are desired. In this paper the development of a method based on the unsteady, compressible Navier-Stokes equations in two dimensions is described in order to study the physics of flutter for unsteady viscous flow around cascaded vibrating blades at stall. The governing equations are solved by a finite difference technique in boundary fitted coordinates. The numerical scheme uses the Advection Upstream Splitting Method to discretize the convective terms and central differences discretizing the viscous terms of the fully non-linear Navier-Stokes equations on a moving H-type mesh. The unsteady governing equations are explicitly and implicitly marched in time in a time-accurate way using a four stage Runge-Kutta scheme on a parallel computer or an implicit scheme of the Beam-Warming type on a single processor. Turbulence is modelled using the Baldwin-Lomax turbulence model. The blade flutter phenomenon is simulated by imposing a harmonic motion on the blade, which consists of harmonic body translation in two directions and a rotation, allowing an interblade phase angle between neighboring blades. Non-reflecting boundary conditions are used for the unsteady analysis at inlet and outlet of the computational domain. The computations are performed on multiple blade passages in order to account for nonlinear effects. A subsonic massively stalled unsteady flow case in a compressor cascade is studied. The results, compared with experiments and the predictions of other researchers, show reasonable agreement for inviscid and viscous flow cases for the investigated flow situations with respect to the Steady and unsteady pressure distribution on the blade in separated flow areas as well as the aeroelastic damping. The results show the applicability of the scheme for stalled flow around cascaded blades. As expected the viscous and inviscid computations show different results in regions where viscous effects are important, i.e. in separated flow areas. In particular, different predictions for inviscid and viscous flow for the aerodynamic damping for the investigated flow cases are found.

scholarly journals Numerical Investigation of Wake Interaction in a Low Pressure Turbine

1998 ◽  
Author(s):  
Frank Eulitz ◽  
Karl Engel
Keyword(s):  
Phenomenological Study ◽  
Separated Flow ◽  
Low Pressure ◽  
Skin Friction Coefficient ◽  
Boundary Layer Transition ◽  
Navier Stokes ◽  
Layer Transition ◽  
Low Pressure Turbine ◽  
Wake Interaction ◽  
Large Fluctuations

A time-accurate Reynolds-averaged Navier-Stokes solver has been extended for a phenomenological study of wake/bladerow interaction in a low pressure turbine near midspan. To qualitatively account for unsteady laminar-turbulent boundary layer transition, a variant of the Abu-Ghanam Shaw transition correlation has been coupled with the Spalart-Allmaras one-equation turbulence model. The method is shown to be capable of capturing separated-flow and wake-induced transition, as well as becalming and relaminarization effects. The model turbine investigated consists of three stator and two rotor rows. Instantaneous Mach number and eddy-viscosity plots are presented to monitor the wake migration and interaction with downstream boundary layers. Especially on the suction sides, very large fluctuations of the skin friction coefficient are observed. Effects of the near and far wakes are identified.

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.

Aerodynamic design and optimization of propellers for multirotor

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Witold Artur Klimczyk
Keyword(s):  
Structural Integrity ◽  
Navier Stokes ◽  
Optimization Approach ◽  
Minimum Thickness ◽  
Design Problems ◽  
Content Type ◽  
Design And Optimization ◽  
Propeller Design ◽  
Unmanned Air Vehicle ◽  
Propeller Blades

Purpose This paper aims to present a methodology of designing a custom propeller for specified needs. The example of propeller design for large unmanned air vehicle (UAV) is considered. Design/methodology/approach Starting from low fidelity Blade Element (BE) methods, the design is obtained using evolutionary algorithm-driven process. Realistic constraints are used, including minimum thickness required for stiffness, as well as manufacturing ones – including leading and trailing edge limits. Hence, the interactions between propellers in hex-rotor configuration, and their influence on structural integrity of the UAV are investigated. Unsteady Reynolds-Averaged Navier–Stokes (URANS) are used to obtain loading on the propeller blades in hover. Optimization of the propeller by designing a problem-specific airfoil using surrogate modeling-driven optimization process is performed. Findings The methodology described in the current paper proved to deliver an efficient blade. The optimization approach allowed to further improve the blade efficiency, with power consumption at hover reduced by around 7%. Practical implications The methodology can be generalized to any blade design problem. Depending on the requirements and constraints the result will be different. Originality/value Current work deals with the relatively new class of design problems, where very specific requirements are put on the propellers. Depending on these requirements, the optimum blade geometry may vary significantly.

Compressor Blade Optimization Using a Continuous Adjoint Formulation

2006 ◽  
Author(s):  
Dimitiros I. Papadimitriou ◽  
Kyriakos C. Giannakoglou
Keyword(s):  
Stokes Equations ◽  
Compressor Blade ◽  
Navier Stokes ◽  
Computational Domain ◽  
Navier Stokes Equations ◽  
Adjoint Formulation ◽  
Design Variables ◽  
Gradient Computation ◽  
Geometrical Constraints ◽  
Continuous Adjoint

In this paper, a constrained optimization algorithm is formulated and utilized to improve the aerodynamic performance of a 3D peripheral compressor blade cascade. The cascade efficiency is measured in terms of entropy generation along the developed flowfield, which defines the field objective functional to be minimized. Its gradient with respect to the design variables, which are the coordinates of the Non-Uniform Rational B-Spline (NURBS) control points defining the blade, is computed through a continuous adjoint formulation of the Navier-Stokes equations based on the aforementioned functional. The steepest descent algorithm is used to locate the optimal set of design variables, i.e. the optimal blade shape. In addition to the well-known advantages of the adjoint method, the current formulation has even less CPU cost for the gradient computation as it leads to gradient expression which is free of field variations in geometrical quantities (such as derivatives of interior grid node coordinates with respect to the design variables); the computation of the latter would be costly since it requires remeshing anew the computational domain for each bifurcated design variable. The geometrical constraints, which depend solely on the blade parameterization, are handled by a quadratic penalty method by introducing additional Lagrange multipliers.

scholarly journals A numerical evaluation of the asymptotic theory of receptivity for subsonic compressible boundary layers

2015 ◽  
Vol 771 ◽  
pp. 520-546 ◽  
Author(s):  
Nicola De Tullio ◽  
Anatoly I. Ruban
Keyword(s):  
Mach Number ◽  
Boundary Layers ◽  
Asymptotic Theory ◽  
Stokes Equations ◽  
Roughness Element ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Compressible Boundary Layers ◽  
Tollmien Schlichting ◽  
Low Amplitude

The capabilities of the triple-deck theory of receptivity for subsonic compressible boundary layers have been thoroughly investigated through comparisons with numerical simulations of the compressible Navier–Stokes equations. The analysis focused on the two Tollmien–Schlichting wave linear receptivity problems arising due to the interaction between a low-amplitude acoustic wave and a small isolated roughness element, and the low-amplitude time-periodic vibrations of a ribbon placed on the wall of a flat plate. A parametric study was carried out to look at the effects of roughness element and vibrating ribbon longitudinal dimensions, Reynolds number, Mach number and Tollmien–Schlichting wave frequency. The flat plate is considered isothermal, with a temperature equal to the laminar adiabatic-wall temperature. Numerical simulations of the full and the linearised compressible Navier–Stokes equations have been carried out using high-order finite differences to obtain, respectively, the steady basic flows and the unsteady disturbance fields for the different flow configurations analysed. The results show that the asymptotic theory and the Navier–Stokes simulations are in good agreement. The initial Tollmien–Schlichting wave amplitudes and, in particular, the trends indicated by the theory across the whole parameter space are in excellent agreement with the numerical results. An important finding of the present study is that the behaviour of the theoretical solutions obtained for $\mathit{Re}\rightarrow \infty$ holds at finite Reynolds numbers and the only conditions needed for the theoretical predictions to be accurate are that the receptivity process be linear and the free-stream Mach number be subsonic.

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