Numerical Modelling of Fluid-Structure Interaction in a Turbine Stage for 3D Viscous Flow in Nominal and Off- Design Regimes

2010 ◽  
Author(s):  
Romuald Rzadkowski ◽  
Vitaly Gnesin ◽  
Lubov Kolodyazhnaya
Keyword(s):  
Boundary Layer ◽  
Viscous Flow ◽  
Gas Turbines ◽  
Element Model ◽  
Boundary Layer Separation ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Flow Distortion ◽  
Boundary Layer Interaction

In recent years there have been major developments in turbomachinery aeroelasticity methods. There are now greater possibilities to predict blade vibrations arising from self-excitation or inlet flow distortion. This is not only important with regard to aircraft compressor and fan blade rows, but also in the case of the last stages of steam and gas turbines working in highly loaded off-design conditions. In order to predict the unsteady pressure loads and aeroelastic behaviour of blades (including the computation of shock waves, shock/boundary layer interaction and boundary layer separation), complete Reynolds-averaged Navier-Stokes (RANS) equations are used in modelling complex and off-design cases of turbomachinery flows. In this paper the 3D RANS solver, including a modified Baldwin and Lomax algebraic eddy viscous turbulence model, is presented to calculate unsteady viscous flow through the turbine stage, while taking into account the blade oscillations but without the separating of outer excitation and unsteady effects caused by blade motion. The numerical method uses the second order by time and coordinates an explicit finite-volume Godunov’s type difference scheme and a moving H-O structured grid. The structure analysis uses the modal approach and a 3D finite element model of blade. To validate the numerical viscous code, the numerical calculation results were compared with the 11th Standard Configuration measurements. Presented here are the numerical analysis results for the aeroelastic behaviour of a steam turbine last stage with 760 mm rotor blades in a nominal and an off-design regime.

Unsteady Operation of a Highly Supersonic Organic Rankine Cycle Turbine

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Enrico Rinaldi ◽  
Rene Pecnik ◽  
Piero Colonna
Keyword(s):  
Boundary Layer ◽  
Organic Rankine Cycle ◽  
Suction Side ◽  
Rankine Cycle ◽  
Boundary Layer Separation ◽  
Expansion Ratio ◽  
Ideal Gas ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Shock Interactions

Organic Rankine cycle (ORC) turbogenerators are the most viable option to convert sustainable energy sources in the low-to-medium power output range (from tens of kWe to several MWe). The design of efficient ORC turbines is particularly challenging due to their inherent unsteady nature (high expansion ratios and low speed of sound of organic compounds) and to the fact that the expansion encompasses thermodynamic states in the dense vapor region, where the ideal gas assumption does not hold. This work investigates the unsteady nonideal fluid dynamics and performance of a high expansion ratio ORC turbine by means of detailed Reynolds-averaged Navier–Stokes (RANS) simulations. The complex shock interactions resulting from the supersonic flow (M ≈ 2.8 at the vanes exit) are related to the blade loading, which can fluctuate up to 60% of the time-averaged value. A detailed loss analysis shows that shock-induced boundary layer separation on the suction side of the rotor blades is responsible for most of the losses in the rotor, and that further significant contributions are given by the boundary layer in the diverging part of the stator and by trailing edge losses. Efficiency loss due to unsteady interactions is quantified in 1.4% in absolute percentage points at design rotational speed. Thermophysical properties are found to feature large variations due to temperature even after the strong expansion in the nozzle vanes, thus supporting the use of accurate fluid models in the whole turbine stage.

Effect of Scaling of Blade Row Sectors on the Prediction of Aerodynamic Forcing in a Highly-Loaded Transonic Turbine Stage

2011 ◽  
Author(s):  
Seyed Mohammad Hosseini ◽  
Florian Fruth ◽  
Damian M. Vogt ◽  
Torsten H. Fransson
Keyword(s):  
Structural Characteristics ◽  
High Sensitivity ◽  
Element Model ◽  
General Purpose ◽  
Forced Response ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Reference Case ◽  
Scaling Technique

The viability of a scaling technique in prediction of forced response of the stator and rotor blades in a turbine stage has been examined. Accordingly the so called parameter, generalized force, is defined which describes the excitation of a modeshape due to the unsteady flow forces at a certain frequency. The capability of this method to accurately predict the generalized forces serves as the viability criterion. The scaling technique modifies the geometry to obtain an integer stator, rotor blade count ratio in an annulus section while maintaining steady aerodynamic similarity. A non-scaled configuration is set up to serve as the reference case. Further configurations with different scaling ratios are also generated for accuracy comparison. Unsteady forces are calculated through 3D Navier-Stokes simulations by VolSol, which is based on an explicit, time-marching. A general purpose finite element model of blades is also provided to enable modal analysis with the harmonic forces. The generalized forces of stator and rotor blades revealed high sensitivity towards modification of stator blades while acceptable accuracy was obtained by moderate modifications of the rotor blades for first harmonic forces. Moreover the influence of variable blade’s structural characteristics proved to be remarkable.

CFD Analysis of Micro-Ramps for Hypersonic Flows

2014 ◽  
Vol 592-594 ◽  
pp. 1962-1966
Author(s):  
Ashish Mogrekar ◽  
Ramasami Sivakumar
Keyword(s):  
Boundary Layer ◽  
Passive Control ◽  
Boundary Layer Separation ◽  
Hypersonic Flows ◽  
Stable Operation ◽  
Cfd Analysis ◽  
Flow Distortion ◽  
Crucial Component ◽  
Study Results ◽  
Boundary Layer Interaction

Air intake is a crucial component for supersonic and hypersonic air breathing propulsion devices. The intake must provide the required mass flow rate of air with minimal loss of stagnation pressure. A major difficulty in the stable operation of an intake is associated with shock wave boundary layer interaction (SBLI). This causes boundary layer separation and adverse pressure gradients which lead to total pressure loss, flow unsteadiness and flow distortion in the intake system. Passive control devices such as micro-ramp, thick-vanes provide better boundary layer control and reduce parasitic drag. The proposed study aims to perform CFD analysis of micro-ramp for hypersonic flows and validate the results with the available experimental data. Two micro ramp models namely MR80 and MR40 are considered for this study. Results obtained show the presence of micro ramp successfully delayed the flow separation and helped to suppress SBLI.

Performance and Boundary Layer Development of a High Turning Compressor Cascade at Sub- and Supercritical Flow Conditions

2012 ◽  
Author(s):  
Christoph Bode ◽  
Dragan Kožulović ◽  
Udo Stark ◽  
Heinz Hoheisel
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Density Ratio ◽  
Boundary Layer Separation ◽  
Experimental Results ◽  
Numerical Code ◽  
Compressor Cascade ◽  
Boundary Layer Development ◽  
Boundary Layer Interaction ◽  
Inlet Angle

Based on current numerical investigations, the present paper reports on new Q2D midspan-calculations and results for the well known high turning (Δβ = 50°) supercritical (Ma1 = 0.85) compressor cascade V2. A Q2D treatment of the problem was chosen in order to avoid the difficult modelling of the porous endwalls in a corresponding 3D approach. All simulations were done with the RANS solver TRACE of the DLR Cologne in combination with modified versions of the Wilcox turbulence model and Langtry/Menter transition model. Existing experimental Q2D midspan-results for the V2 compressor cascade were used to demonstrate the improved ability of the numerical code to determine performance characteristics, blade pressure and Mach number distributions as well as boundary layer parameter and velocity distributions. The loss characteristics show minimum loss regions when plotted against inlet angle or axial velocity density ratio. Within these regions, increasing with decreasing Mach number, the experimental results were adequately predicted. Outside these regions it turned out difficult to reproduce the experimental results due to increasing boundary layer separation. Furthermore, the prediction quality was very good for subsonic conditions (Ma1 = 0.60) and still reasonable for supercritical conditions (Ma1 = 0.85), where shock/boundary layer interaction made the prediction more difficult.

Comparison of Inviscid Computations With Theory and Experiment in Vibrating Transonic Compressor Cascades

1990 ◽  
Author(s):  
G. A. Gerolymos ◽  
E. Blin ◽  
H. Quiniou
Keyword(s):  
Boundary Layer ◽  
Plate Theory ◽  
Strong Shock ◽  
Acoustic Resonance ◽  
Boundary Layer Separation ◽  
Computational Method ◽  
Viscous Effects ◽  
Transonic Compressor ◽  
Boundary Layer Interaction ◽  
Interaction Regions

The prediction of unsteady flow in vibrating transonic cascades is essential in assessing the aeroelastic stability of fans and compressors. In the present work an existing computational code, based on the numerical integration of the unsteady Euler equations, in blade-to-blade surface formulation, is validated by comparison with available theoretical and experimental results. Comparison with the flat plate theory of Verdon is, globally, satisfactory. Nevertheless, the computational results do not exhibit any particular behaviour at acoustic resonance. The use of a 1-D nonreflecting boundary condition does not significantly alter the results. Comparison of the computational method with experimental data from started and unstarted supersonic flows, with strong shock waves, reveals that, notwithstanding the globally satisfactory performance of the method, viscous effects are prominent at the shock wave/boundary layer interaction regions, where boundary layer separation introduces a pressure harmonic phase shift, which is not presicted by inviscid methods.

Self-Excited Oscillation of Transonic Flow Around an Airfoil in Two-Dimensional Channel

1989 ◽  
Author(s):  
Kazuomi Yamamoto ◽  
Yoshimichi Tanida
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Transonic Flow ◽  
Stokes Equations ◽  
Flow Region ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Layer Separation ◽  
Excited Oscillation

A self-excited oscillation of transonic flow in a simplified cascade model was investigated experimentally, theoretically and numerically. The measurements of the shock wave and wake motions, and unsteady static pressure field predict a closed loop mechanism, in which the pressure disturbance, that is generated by the oscillation of boundary layer separation, propagates upstream in the main flow and forces the shock wave to oscillate, and then the shock oscillation disturbs the boundary layer separation again. A one-dimensional analysis confirms that the self-excited oscillation occurs in the proposed mechanism. Finally, a numerical simulation of the Navier-Stokes equations reveals the unsteady flow structure of the reversed flow region around the trailing edge, which induces the large flow separation to bring about the anti-phase oscillation.

scholarly journals СНИЖЕНИЕ ВИБРОНАПРЯЖЕННОСТИ ПОПАРНО БАНДАЖИРОВАННЫХ РАБОЧИХ ЛОПАТОК ТУРБИНЫ

2020 ◽  
pp. 52-58
Author(s):  
Юрий Петрович Кухтин ◽  
Руслан Юрьевич Шакало
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Stokes Equations ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Navier Stokes ◽  
Turbine Stage ◽  
Turbine Engine ◽  
Exciting Forces ◽  
Working Blades

To reduce the vibration stresses arising in the working blades of turbines during resonant excitations caused by the frequency of passage of the blades of the nozzle apparatus, it is necessary to control the level of aerodynamic exciting forces. One of the ways to reduce dynamic stresses in rotor blades under operating conditions close to resonant, in addition to structural damping, maybe to reduce external exciting forces. To weaken the intensity of the exciting forces, it is possible to use a nozzle apparatus with multi-step gratings, as well as with non-radially mounted blades of the nozzle apparatus.This article presents the results of numerical calculations of exciting aerodynamic forces, as well as the results of experimental measurements of stresses arising in pairwise bandaged working blades with a frequency zCA ⋅ fn, where fn – is the rotor speed, zCA – is the number of nozzle blades. The object of research was the high-pressure turbine stage of a gas turbine engine. Two variants of a turbine stage were investigated: with the initial geometry of the nozzle apparatus having the same geometric neck area in each interscapular channel and with the geometry of the nozzle apparatus obtained by alternating two types of sectors with a reduced and initial throat area.The presented results are obtained on the basis of numerical simulation of a viscous unsteady gas flow in a transonic turbine stage using the SUnFlow home code, which implements a numerical solution of the Reynolds-averaged Navier-Stokes equations. Discontinuity of a torrent running on rotor blades is aggravated with heat drops between an ardent flow core and cold jets from film cooling of a blade and escapes on clock surfaces. Therefore, at simulation have been allowed all blowngs cooling air and drain on junctions of shelves the impeller.As a result of the replacement of the nozzle apparatus with a constant passage area by a nozzle apparatus with a variable area, a decrease in aerodynamic driving force by 12.5 % was obtained. The experimentally measured stresses arising in a pairwise bandaged blade under the action of this force decreased on average by 26 %.

Analysis of Physical Processes in the Flow Parts of Gas Turbines with Different Blade Chords

2021 ◽  
pp. 40-53
Author(s):  
V.D. Molyakov ◽  
B.A. Kunikeev ◽  
N.I. Troitskiy
Keyword(s):  
Flow Structure ◽  
Gas Turbines ◽  
Relative Elongation ◽  
Experimental Studies ◽  
Flow Path ◽  
Rotor Blades ◽  
Turbine Stage ◽  
Physical Processes ◽  
Integral Characteristics ◽  
Flow Part

Theoretical and experimental studies of the current flowing in the lattices of the turbine stage impeller with a change in the elongation of its blades at constant constraining diameters of the flow part (constant blade lengths) are carried out. Four single-stage turbines with different chords of rotor blades and their relative elongations have been investigated. To explain the nature of the integral characteristics of the turbine stage with a change in the relative elongation of the rotor blades, detailed studies of the spatial flow structure in the gap between wheels and behind the impeller were carried out. The peculiarity of the operation of four impellers in the turbine stage is shown when the geometry of the channels changes along the height of the flow path - from active at the root to highly reactive at the periphery. A characteristic redistribution of the local values of the efficiency and losses along the height of the lattices associated with a change in the elongation of the rotor blades and the rotation of the lattices has been revealed. It was found that with a decrease in the elongation of the rotor blades, the zone with the minimum efficiency moves from the root sections to the peripheral ones with its simultaneous restructuring and an increase in the minimum efficiency in this zone. In this case, the integral values of the efficiency of impellers with different relative elongations of the blades remain the same and sufficiently high.

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