Search results

1 – 10 of 225
Article
Publication date: 29 August 2019

Bo Zhang, Xiaoqing Qiang, Shaopeng Lu and Jinfang Teng

The purpose of this paper is to numerically investigate the effect of guide vane unsteady passing wake on the rotor blade tip aerothermal performance with different tip clearances.

Abstract

Purpose

The purpose of this paper is to numerically investigate the effect of guide vane unsteady passing wake on the rotor blade tip aerothermal performance with different tip clearances.

Design/methodology/approach

The geometry and flow conditions of the first stage of GE-E3 high-pressure turbine have been used to obtain the blade tip three-dimensional heat transfer characteristics. The first stage of GE-E3 high-pressure turbine has 46 guide vanes and 76 rotor blades, and the ratio of the vane to the blade is simplified to 38:76 to compromise the computational resources and accuracy. Namely, each computational domain comprises of one guide vane passage and two rotor blade passages. The investigations are conducted at three different tip gaps of 1.0, 1.5 and 2.0 per cent of the average blade span.

Findings

The results show that the overall discrepancy of the heat transfer coefficient between steady results and unsteady time-averaged results is quite small, but the dramatic growth of the instantaneous heat transfer coefficient along the pressure side is in excess of 20 per cent. The change of the aerothermal performance is mainly driven by turbulence-level fluctuations of the unsteady flow field within gap regions. In addition, the gap size expansion has a marginal impact on the variation ratio of tip unsteady aerothermal performances, even though it has a huge influence on the leakage flow state within the tip region.

Originality/value

This paper emphasizes the change ratio of unsteady instantaneous heat transfer characteristics and detailed the mechanism of blade tip unsteady heat transfer coefficient fluctuations, which provide some guidance for the future blade tip design and optimization.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 29 March 2011

J.M. Fernández Oro, K.M. Argüelles Diaz, C. Santolaria Morros and M. Galdo Vega

The purpose of this paper is to focus on the analysis of the dynamic and periodic interaction between both fixed and rotating blade rows in a single‐stage turbomachine.

Abstract

Purpose

The purpose of this paper is to focus on the analysis of the dynamic and periodic interaction between both fixed and rotating blade rows in a single‐stage turbomachine.

Design/methodology/approach

A numerical three‐dimensional (3D) simulation of the complete stage is carried out, using a commercial code, FLUENT, that resolves the 3D, unsteady turbulent flow inside the passages of a low‐speed axial flow fan. For the closure of turbulence, both Reynolds‐averaged Navier‐Stokes modeling and large eddy simulation (LES) techniques are used and compared. LES schemes are shown to be more accurate due to their good description of the largest eddy structures of the flow, but require careful near‐wall treatment.

Findings

The main goal is placed on the characterization of the unsteady flow structures involved in an axial flow blower of high reaction degree, relating them to working point variations and axial gap modifications.

Research limitations/implications

Complementarily, an experimental facility was developed to obtain a physical description of the flow inside the machine. Both static and dynamic measurements were used in order to describe the interaction phenomena. A five‐hole probe was employed for the static characterization, and hot wire anemometry techniques were used for the instantaneous response of the interaction.

Originality/value

The paper describes development of a methodology to understand the flow mechanisms related to the blade‐passing frequency in a single rotor‐stator interaction.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 21 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 30 October 2018

Jesús Manuel Fernandez Oro, Andrés Meana-Fernández, Monica Galdo Vega, Bruno Pereiras and José González Pérez

The purpose of this paper is the development of a CFD methodology based on LES computations to analyze the rotor–stator interaction in an axial fan stage.

Abstract

Purpose

The purpose of this paper is the development of a CFD methodology based on LES computations to analyze the rotor–stator interaction in an axial fan stage.

Design/methodology/approach

A wall-modeled large eddy simulation (WMLES) has been performed for a spanwise 3D extrusion of the central section of the fan stage. Computations were performed for three different operating conditions, from nominal (Q_N) to off-design (85 per cent Q_N and 70 per cent Q_N) working points. Circumferential periodic conditions were introduced to reduce the extent of the computational domain. The post-processing procedure enabled the segregation of unsteady deterministic features and turbulent scales. The simulations were experimentally validated using wake profiles and turbulent scales obtained from hot-wire measurements.

Findings

The transport of rotor wakes and both wake–vane and wakewake interactions in the stator flow field have been analyzed. The description of flow separation, particularly at off-design conditions, is fully benefited from the LES performance. Rotor wakes impinging on the stator vanes generate a coherent large-scale vortex shedding at reduced frequencies. Large pressure fluctuations in the stagnation region on the leading edge of the vanes have been found.

Research limitations/implications

LES simulations have shown to be appropriate for the assessment of the design of an axial fan, especially for specific operating conditions for which a URANS model presents a lower performance for turbulence description.

Originality/value

This paper describes the development of an LES-based simulation to understand the flow mechanisms related to the rotor–stator interaction in axial fan stages.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 11 January 2020

Adrián Vazquez Gonzalez, Andrés Meana-Fernández and Jesús Manuel Fernández

The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF…

Abstract

Purpose

The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan.

Design/methodology/approach

A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region.

Findings

It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes.

Research limitations/implications

Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy.

Originality/value

The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 10
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 February 2022

Surekha Rathi Samundi D. and Rajasekar R.

This study aims to investigate the wake behind an oscillating airfoil at a various angle of incidence and Reynolds number in a deep dynamic stall condition.

Abstract

Purpose

This study aims to investigate the wake behind an oscillating airfoil at a various angle of incidence and Reynolds number in a deep dynamic stall condition.

Design/methodology/approach

NACA 0012 airfoil is allowed to undergo harmonic pitching motion about the quarter chord axis at Reynolds numbers of 0.5 * 105, 1.17 * 105, 1.7 * 105 and 2.12 * 105, and the reduced frequency of 0.1. The experiments are conducted at a set of mean and amplitude angle of attack that covered the angle of incidence from −5° to 25°. The wake rake is placed at a distance of one chord from the trailing edge of the airfoil.

Findings

The hysteresis of the flow during the upstroke and the downstroke motion are captured. The huge growth in the velocity defect and the wake thickness beyond the angle of attack of 15° explicate the appearance of the strong unsteady effects on the wake. The results also show that at the reduced frequency of 0.1, the wake structure is of drag producing type due to the momentum deficit.

Originality/value

Streamwise velocity profile and the turbulent intensity profiles are presented to show the effects of Reynolds number and angle of incidence on the wake behind the oscillating airfoil at the reduced frequency of 0.1, and in the intermediate range of Reynolds number is the novelty of the study.

Details

Aircraft Engineering and Aerospace Technology, vol. 94 no. 6
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 4 September 2017

Anton Stephan, Frank Holzäpfel and Stefan Zholtovski

This study aims to investigate the effect of gusts on aircraft wake vortices. Aircraft wake vortices present a potential risk to following aircraft, particularly during final…

Abstract

Purpose

This study aims to investigate the effect of gusts on aircraft wake vortices. Aircraft wake vortices present a potential risk to following aircraft, particularly during final approach and landing, as wake vortices may remain in the flight corridor for a long time. Wind and turbulence are key factors that influence the wake vortex evolution and the wake vortex generation in the aircraft. Flying through a gust influences the wake vortex roll-up process and its evolution. Note that vertical and lateral gusts may affect counter-rotating wake vortices differently. Both vortices influence each other by inducing a downward velocity. Disturbances may therefore lead to local vortex tilting and later to a complex three-dimensional deformation. This work uses two different hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation (RANS-LES) approaches to investigate the effect of gusts on wake vortex evolution. In a one-way coupling, a pre-calculated RANS velocity field of the aircraft’s near-field is being swept through an LES domain. The effect of a sine gust on the turbulent wake is modeled by manipulating the RANS-field accordingly. As a more sophisticated approach, the concept of a two-way coupling is being presented. Here an LES solver is bi-directionally coupled with an unsteady RANS (URANS) solver, exchanging values at every physical time step of the simulation.

Design/methodology/approach

A one-way coupling approach of the LES code MGLET and the RANS code TAU is presented to simulate the gust effect on aircraft wake vortices. Additionally, the concept of the two-way coupling of these two codes incorporating a coupling module.

Findings

The gust effect of wake vortices subjected to a crosswind can be simulated. The vortex physics is analyzed. Unexpected behavior like fast upwind vortex decay is revealed.

Practical implications

The understanding of the aircraft wake vortex physics during landing provides valuable information for wake vortex advisory systems.

Originality/value

The effect of gust on wake vortices during and after landing has not been studied so far. The hybrid one-way coupling approach, as well as the concept of the two-way coupling, are relatively new.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 5
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 8 March 2011

Xiao Yexiang, Wang Zhengwei and Yan Zongguo

The purpose of this paper is to investigate, experimentally and numerically, the pressure pulse characteristics and unsteady flow behavior in a Francis turbine runner for moderate…

Abstract

Purpose

The purpose of this paper is to investigate, experimentally and numerically, the pressure pulse characteristics and unsteady flow behavior in a Francis turbine runner for moderate flow heads. The pressure pulses in the runner blade passage were predicted numerically for both moderate and high heads. The calculations were used to partition the turbine operating regions and to clarify the various for the unsteady flow behavior, especially the blade channel vortex in the runner.

Design/methodology/approach

Experimental and numerical analyses of pressure pulse characteristics at moderate flow heads in a Francis turbine runner were then extended to high heads through numerical modeling with 3D unsteady numerical simulations performed for a number of operating conditions. The unsteady Reynolds‐averaged Navier‐Stokes equations with the k‐ω‐based shear stress transport turbulence model were used to model the unsteady flow within the entire flow passage of a Francis turbine.

Findings

The dominate frequency of the predicted pressure pulses at runner inlet agree with the experimental results in the head cover at moderate flow heads. The influence of the blade passing frequency causes the simulated peak‐to‐peak amplitudes in the runner inlet to be larger than in the head cover. The measured and predicted pressure pulses at different positions along the runner are comparable. At the most unstable operating condition of 0.5a0 guide vane opening, the pressure pulses in the runner blade passage are due to the blade channel vortex and the rotor‐stator interference. The predictions show that the frequency of the blade channel vortex is relatively low and it changes with the operating conditions.

Originality/value

The paper describes a study which experimentally and numerically investigated the pressure pulses characteristics in a Francis turbine runner at moderate flow heads. The pulse characteristics and unsteady flow behavior due to the blade channel vortex in the runner at high heads were investigated numerically, with the turbine operating regions then partitioned to identify safe operating regions.

Details

Engineering Computations, vol. 28 no. 2
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 3 April 2018

Somayeh Harimi, Azam Marjani and Sadegh Moradi

This paper aims to study the fluid flow and forced convection heat transfer from an isothermal circular cylinder with control rods in the laminar unsteady flow regime.

Abstract

Purpose

This paper aims to study the fluid flow and forced convection heat transfer from an isothermal circular cylinder with control rods in the laminar unsteady flow regime.

Design/methodology/approach

The overset grid method was used for accurate simulation of the unsteady flows around different arrangements of the cylinders. Grid generation for overset grids was performed using a general orthogonal boundary fitted coordinate system. The method of solution was based on a finite volume discretization of the Navier-Stokes equations. Simulations were carried out for the Prandtl numbers of 0.7 and 7.0 with the Reynolds numbers ranging from 60 to 300.

Findings

The results indicate that the performance of multiple control rods depends strongly on the spacing ratio. Furthermore, in a manner similar to the flow patterns, four different thermal regimes were recognized based on the variations of mean Nusselt number versus G/D, as the thermal regimes follow the categories of flow regimes at different diameter ratios. However, for different Prandtl numbers, no single trend of heat transfer variation versus the spacing ratio exists for same regime.

Originality/value

Few studies have been conducted to investigate the heat transfer characteristics from control rods. The results of this study provide a comprehensive knowledge on the dynamical and thermal behavior of the flow around multiple cylinders.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 6 January 2012

Sung In Kim, Hamidur Rahman and Ibrahim Hassan

One of the most critical gas turbine engine components, the rotor blade tip and casing, is exposed to high thermal load. It becomes a significant design challenge to protect the…

Abstract

Purpose

One of the most critical gas turbine engine components, the rotor blade tip and casing, is exposed to high thermal load. It becomes a significant design challenge to protect the turbine materials from this severe situation. The purpose of this paper is to study numerically the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer.

Design/methodology/approach

In this paper, the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer has been studied numerically. Uniform low (LTIT: 444 K) and high (HTIT: 800 K) turbine inlet temperature, as well as non‐uniform inlet temperature have been considered.

Findings

The results showed the higher turbine inlet temperature yields the higher velocity and temperature variations in the leakage flow aerodynamics and heat transfer. For a given turbine geometry and on‐design operating conditions, the turbine power output can be increased by 1.33 times, when the turbine inlet temperature increases 1.80 times. Whereas the averaged heat fluxes on the casing and the blade tip become 2.71 and 2.82 times larger, respectively. Therefore, about 2.8 times larger cooling capacity is required to keep the same turbine material temperature. Furthermore, the maximum heat flux on the blade tip of high turbine inlet temperature case reaches up to 3.348 times larger than that of LTIT case. The effect of the interaction of stator and rotor on heat transfer features is also explored using unsteady simulations. The non‐uniform turbine inlet temperature enhances the heat flux fluctuation on the blade tip and casing.

Originality/value

The increase of turbine inlet temperature is usually proposed to achieve the higher turbine efficiency and the higher turbine power output. However, it has not been reported how much the heat transfer into the blade tip and casing increases with the increased turbine inlet temperature. This paper investigates the heat transfer distributions on the rotor blade tip and casing, associated with the tip leakage flow under high and low turbine inlet temperatures, as well as non‐uniform temperature distribution.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 22 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 2 May 2017

Joshua Gottlieb, Roger Davis and John Clark

The authors aim to present a procedure for the parallel, steady and unsteady conjugate, Navier–Stokes/heat-conduction rotor-stator interaction analysis of multi-blade-row…

Abstract

Purpose

The authors aim to present a procedure for the parallel, steady and unsteady conjugate, Navier–Stokes/heat-conduction rotor-stator interaction analysis of multi-blade-row, film-cooled, turbine airfoil sections. A new grid generation procedure for multiple blade-row configurations, including walls, thermal barrier coatings, plenums, and cooling tubes, is discussed.

Design/methodology/approach

Steady, multi-blade-row interaction effects on the flow and wall thermal fields are predicted using a Reynolds’s-averaged Navier–Stokes (RANS) simulation in conjunction with an inter-blade-row mixing plane. Unsteady, aero-thermal interaction solutions are determined using time-accurate sliding grids between the stator and rotor with an unsteady RANS model. Non-reflecting boundary condition treatments are utilized in both steady and unsteady approaches at all inlet, exit and inter-blade-row boundaries. Parallelization techniques are also discussed.

Findings

The procedures developed in this research are compared against experimental data from the Air Force Research Laboratory’s turbine research facility.

Practical implications

The software presented in this paper is useful as both the design and analysis tool for fluid system and turbomachinery engineers.

Originality/value

This research presents a novel approach for the simultaneous solution of fluid flow and heat transfer in film-cooled rotating turbine sections. The software developed in this research is validated against experimental results for 2D flow, and the methods discussed are extendable to 3D.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 3
Type: Research Article
ISSN: 1748-8842

Keywords

1 – 10 of 225