URANS of flow and endwall heat transfer in a pinned passage relevant to gas-turbine blade cooling

This paper presents some results of URANS study of flow and heat transfer in a matrix of wall-bounded 8 × 8 round pins, mimicking internal cooling passage of gas-turbine blades. The focus is on flow unsteadiness, its role in heat transfer and the capabilities of RANS models to reproduce these features in a set-up of industrial relevance. The results for two Reynolds numbers, 10 000 and 30 000, are compared with the available experiments and LES. It is shown that the elliptic-relaxation eddy-viscosity model, ζ-f captures vortex shedding and the consequent gross effects on the flow development. However, a closer look at flow details reveals discrepancies, especially around the first three pin rows, where the unsteadiness reproduced by URANS shows much weaker amplitudes as compared with LES. Only further downstream the succession of forcing from a series of pins produced unsteadiness akin to those captured by LES. The comparison suggests that smaller structures undetected by URANS need to be resolved to capture properly the separation and wake characteristics of each row. At Re = 10 000, the average endwall Nusselt number agrees well with the LES, both being about 20% lower than in the experiment. For Re = 30 000 the URANS Nusselt is within 10% of the experimental value.     

Air-cooled gas-turbine discs: a review of recent research

The flow between corotating compressor or turbine discs and the flow between a turbine disc and an adjacent stationary casing can be respectively modelled by a rotating cavity and by a rotor-stator system. This paper reviews some of the recent experimental and theoretical work on flow and heat transfer in these two classes of rotating-disc systems. Comparisons between the theoretical and measured distributions of velocity, pressure, and Nusselt numbers are made for the rotating cavity with a superimposed radial flow of cooling air. For the rotor-stator system, some recent work on the fluid dynamics is outlined, and particular mention is made of the so-called “ingress problem” and of the use of pre-swirl air to improve the blade-cooling effectiveness.     

Computational fluid dynamics analysis of diffuser performance in gas-powered jet pumps

Jet pump diffuser performance is analyzed, both in terms of past experimental work dealing with the high inlet flow distortions involved and in the sense that this problem is amenable to predictive investigation by computational fluid dynamics techniques. In these highly nonuniform flow conditions, diffusers are seen to justify their inclusion in a jet pump design, for regaining static pressure downstream of the vacuum chamber, even though their performance in effectiveness terms is lowered by about two thirds at high inlet glow distortion levels. A satisfactory correlation has been found between outlet and inlet conditions and diffuser area ratio, extending well beyond past experimental published results for diffuser geometry and distorted inlet flows.     

Nonlinear dynamics of a pipe conveying pulsating fluid with parametric and internal resonances

In this paper, the nonlinear planar vibration of a pipe conveying pulsatile fluid subjected to principal parametric resonance in the presence of internal resonance is investigated. The pipe is hinged to two immovable supports at both ends and conveys fluid at a velocity with a harmonically varying component over a constant mean velocity. The geometric cubic nonlinearity in the equation of motion is due to stretching effect of the pipe. The natural frequency of the second mode is approximately three times the natural frequency of the first mode for a range of mean flow velocity, resulting in a three-to-one internal resonance. The analysis is done using the method of multiple scales (MMS) by directly attacking the governing nonlinear integral-partial-differential equations and the associated boundary conditions. The resulting set of first-order ordinary differential equations governing the modulation of amplitude and phase is analyzed numerically for principal parametric resonance of first mode. Stability, bifurcation, and response behavior of the pipe are investigated. The results show new zones of instability due to the presence of internal resonance. A wide array of dynamical behavior is observed, illustrating the influence of internal resonance.     

Computational fluid dynamics simulations of aerosol behavior in a high-speed (Heubach) rotating drum dustiness tester

Potential exposure from hazardous dust may be assessed by evaluating the dustiness of the powders being handled. Dustiness is the tendency of a powder to aerosolize with a given input of energy. Previously we used computational fluid dynamics (CFD) to numerically investigate the flow inside the European Standard (EN15051) rotating drum dustiness tester during its operation. The present work extends those CFD studies to the widely used Heubach rotating drum. Air flow characteristics are investigated within the Abe-Kondoh-Nagano k-epsilon turbulence model; the aerosol is incorporated via a Euler-Lagrangian multiphase approach. The air flow inside these drums consists of a well-defined axial jet penetrating relatively quiescent air. The spreading of the Heubach jet results in a fraction of the jet recirculating as back-flow along the drum walls; at high rotation rates, the axial jet becomes unstable. This flow behavior qualitatively differs from the stable EN15051 flow pattern. The aerodynamic instability promotes efficient mixing within the Heubach drum, resulting in higher particle capture efficiencies for particle sizes d < 80 μm.     

Compressible, viscous fluid dynamics (review). Part 1

The article is the first part of a survey of problems in compressible, viscous fluid dynamics as related to the dynamics of rigid and elastic bodies in a compressible, viscous fluid in the linearized formulation. The formulation of basic problems is discussed, along with a method of solution based on general solutions of the Navier-Stokes equations in vector and scalar form in dynamical problems. Forced harmonic vibrations of rigid bodies in rest and moving compressible, viscous fluids are discussed. Publications relevant to the stated problems are analyzed. S. P. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev. Translated from Prikladnaya Mekhanika, Vol. 36, No. 1, pp. 25–52, January, 2000. Detailed information about the author can be found in the journalPrikladnaya Mekhanika, Volume 35, No. 1, pp. 104–108 (1999).     

Computational aeroelastic analysis of a hovering W3 Sokol blade with gurney flap

This paper demonstrates the potential effect of a gurney flap on the performance of the W3-Sokol rotor blade in hover. A rigid blade was first considered and the calculations were conducted at several thrust settings. The gurney flap was extended from 46%R to 66%R and it was located at the trailing edge of the main rotor blade. Four different sizes of gurney flaps were studied, 2%, 1%, 0.5% and 0.3% of the chord. The biggest flap proved to be the most effective. A second study considered elastic blades with and without the gurney flap. The results were trimmed at the same thrust values as the rigid blade and indicate an increase of aerodynamic performance when the gurney flap is used, especially for high thrust cases.     

The cooling of a low-heat-resistance sheet moving through a fluid: A rejoinder

Zusammenfassung Diese Notiz behandelt einige Kommentare, die kürzlich in dieser Zeitschrift erschienen sind, zu einer früheren Arbeit über die Abkühlung einer gut wärmeleitenden Platte, die durch eine Flüssigkeit bewegt wird. Es wird explizit gezeigt, daß die Reihenentwicklung in unserer früheren Arbeit in der Tat den Abkühlungsprozeß im ganzen Bereich genau beschreibt. Entgegengesetzte Behauptungen durch Afzal und Varshney entbehren der Grundlage wegen falscher Interpretation divergenter Asymptoten und durch den Gebrauch ungenauer numerischer Daten.

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The cooling of a low-heat-resistance sheet moving through a fluid: A rejoinder

This note deals with some of the comments that appeared recently in this journal on earlier work about the cooling of a low-heat-resistance sheet moving through a fluid. It is shown explicitly that the series expansions in our earlier work do indeed describe accurately the heat-transfer process in the complete domain. The recent evidence brought in against it by Afzal and Varshney is shown to be insufficient due to their misinterpretation of divergent asymptotics and their use of inaccurate numerical data.

     

Computational fluid dynamics simulation of hydrodynamics in the riser of an external loop airlift reactor

Local hydrodynamics in the riser of an external loop airlift reactor (EL-ALR) are identified and the performances of three drag models are evaluated in computational fluid dynamics simulation. The simulation results show that the Schiller–Naumann drag model underestimated the local gas holdup at lower superficial gas velocity whereas the Tomiyama drag model overestimated that at higher superficial gas velocity. By contrast, the dual-bubble-size (DBS)-local drag model gave more reasonable radial and axial distributions of gas holdup in all cases. The reason is that the DBS-local drag model gave correct values of the lumped parameter, i.e., the ratio of the drag coefficient to bubble diameter, for varying operating conditions and radial positions. This ratio is reasonably expected to decrease with increasing superficial gas velocity and be smaller in the center and larger near the wall. Only the DBS-local drag model correctly reproduced these trends. The radial profiles of the axial velocity of the liquid and gas predicted by the DBS-local model also agreed well with experimental data.     

The invariant manifold approach applied to nonlinear dynamics of a rotor-bearing system

The invariant manifold approach is used to explore the dynamics of a nonlinear rotor, by determining the nonlinear normal modes, constructing a reduced order model and evaluating its performance in the case of response to an initial condition. The procedure to determine the approximation of the invariant manifolds is discussed and a strategy to retain the speed dependent effects on the manifolds without solving the eigenvalue problem for each spin speed is presented. The performance of the reduced system is analysed in function of the spin speed.     

The cooling of a low-heat-resistance stretching sheet moving through a fluid: A rejoinder

This note deals with the comments of Kuiken that appeared in the journal disputing the accuracy of the solutions of an earlier work on the cooling of a low heat resistance stretching sheet moving through a fluid. It is shown that there is no loss of accuracy in the higher order perturbations, as claimed by Kuiken. Further, a comparison of the results of Euler transformation with those of Kuiken (based on direct and inverse series) show the agreement to four places of decimal for all values of steamwise distances. The results for heat transfer not considered in earlier papers are also presented here.     

Performance assessment of a non-linear eddy-viscosity turbulence model applied to the anisotropic wake flow of a low-pressure turbine blade

The wake flow produced by a low-pressure turbine blade is modeled using a non-linear eddy-viscosity turbulence model. The theoretical benefit of using a non-linear eddy-viscosity model is strongly related to the capability of resolving highly anisotropic flows in contrast to the linear turbulence models, which are unable to correctly predict anisotropy. The main aim of the present work is to practically assess the performance of the model, by examining its ability to capture the anisotropic behavior of the wake-flow, mainly focusing on the measured velocity and Reynolds-stress distributions and to provide accurate results for the turbulent kinetic energy balance terms. Additionally, the contribution of each term of its non-linear constitutive expression for the Reynolds stresses is also investigated, in order to examine their direct effect on the modeling of the wake flow. The assessment is based on the experimental measurements that have been carried-out by the same group in Thessaloniki, Sideridis et al. (2011). The computational results show that the non-linear eddy viscosity model is capable to predict, with a good accuracy, all the flow and turbulence parameters while it is easy to program it in a computer code thus meeting the expectations of its originators.     

Exploring alternative approaches to computational fluid dynamics

This paper discusses advances in two areas which may have the potential to impact future simulation capabilities through advanced algorithms. This includes spectral multigrid (MG) solvers for high-order accurate spatial discretizations and efficient MG solvers for kinetic-based schemes. Preliminiary evidence is given illustrating the promise of these approaches for application to engineering simulations.     

Computational dynamics: theory and applications of multibody systems

Multibody system dynamics is an essential part of computational dynamics a topic more generally dealing with kinematics and dynamics of rigid and flexible systems, finite elements methods, and numerical methods for synthesis, optimization and control including nonlinear dynamics approaches. The theoretical background of multibody dynamics is presented, the efficiency of recursive algorithms is shown, methods for dynamical analysis are summarized, and applications to vehicle dynamics and biomechanics are reported. In particular, the wear of railway wheels of high-speed trains and the metabolical cost of human locomotion is analyzed using multibody system methods.