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An Unsteady Reynolds‐Averaged Navier‐Stokes (URANS) equation method has been applied to compute the flow over two‐dimensional smooth topography and compared with conventional RANS and large‐eddy simulation (LES) results. The URANS calculation with sufficient grid resolution near solid surface and an appropriate near‐wall model has been shown to simulate much of the large‐scale unsteadiness and some of the turbulent motion for flows with and without separation. Although the results with unadjusted model constants do not show an overwhelming improvement over a standard two‐equation model, it is demonstrated that it may be improved and, more importantly, can be generalized to a new simulation technique by refining the model, considering such factors as grid‐dependent length scales and by making a three‐dimensional calculation.

Understanding the interaction of turbulence and cavitation is an essential step towards better controlling the cavitation phenomenon. The purpose of this paper is to bring out the efficacy of different modelling approaches to predict turbulence and cavitation-induced phase changes.

This paper compares the dynamic cavitation (DCM) and Schnerr–Sauer models. Also, the effects of different modelling methods for turbulence, unsteady Reynolds-averaged Navier–Stokes (URANS) and detached eddy simulations (DES) are also brought out. Numerical predictions of internal flow through a venturi are compared with experimental results from the literature.

The improved predictive capability of cavitating structures by DCM is brought out clearly. The temporal variation of the cavity size and velocity illustrates the involvement of re-entrant jet in cavity shedding. From the vapour fraction contours and the attached cavity length, it is found that the formation of the re-entrant jet is stronger in DES results compared with that by URANS. Variation of pressure, velocity, void fraction and the mass transfer rate at cavity shedding and collapse regions are presented. Wavelet analysis is used to capture the shedding frequency and also the corresponding occurrence of features of cavity collapse.

Based on the performance, computational time and resource requirements, this paper shows that the combination of DES and DCM is the most suitable option for predicting turbulent-cavitating flows.

In recent years, the partially averaged Navier–Stokes (PANS) methodology has earned acceptability as a viable scale-resolving bridging method of turbulence. To further enhance its capabilities, especially for simulating separated flows past bluff bodies, this paper aims to combine PANS with a non-linear eddy viscosity model (NLEVM).

The authors first extract a PANS closure model using the Shih’s quadratic eddy viscosity closure model [originally proposed for Reynolds-averaged Navier–Stokes (RANS) paradigm (Shih et al., 1993)]. Subsequently, they perform an extensive evaluation of the combination (PANS + NLEVM).

The NLEVM + PANS combination shows promising result in terms of reduction of the anisotropy tensor when the filter parameter (f_k) is reduced. Further, the influence of PANS filter parameter f on the magnitude and orientation of the non-linear part of the stress tensor is closely scrutinized. Evaluation of the NLEVM + PANS combination is subsequently performed for flow past a square cylinder at Reynolds number of 22,000. The results show that for the same level of reduction in f_k, the PANS + NLEVM methodology releases significantly more scales of motion and unsteadiness as compared to the traditional linear eddy viscosity model (LEVM) of Boussinesq (PANS + LEVM). The authors further demonstrate that with this enhanced ability the NLEVM + PANS combination shows much-improved predictions of almost all the mean quantities compared to those observed in simulations using LEVM + PANS.

Based on these results, the authors propose the NLEVM + PANS combination as a more potent methodology for reliable prediction of highly separated flow fields.

Combination of a quadratic eddy viscosity closure model with PANS framework for simulating flow past bluff bodies.

The purpose of this paper is to numerically study inflow turbulence effects on the transitional flow in a high pressure linear transonic turbine at the design incidence.

The three‐dimensional (3‐D) compressible turbulent flow in a turbine inlet guide vane is simulated using a finite volume based fluid solver coupled with dynamic large eddy simulation (LES) computations to investigate the effects of varying inflow turbulence length scale and the turbulence intensity on the aero‐thermal flow characteristics and the laminar‐turbulent transition phenomena. The computational analyses are extended to very high exit Reynolds number flow conditions to further study the effect of high exit Reynolds numbers on the transitional behavior of the present flow around the inlet guide vane cascades of the turbine. The calculations are performed with varying degree of inflow turbulence intensity values ranging from 0.8 to 6 percent and the inflow turbulence length scales ranging from one to five percent of pitch for different exit isentropic Mach and Reynolds numbers.

The numerical predictions in comparison with the experimental data demonstrate that the level of inflow turbulence closure provided by the present LES computations offers a reliable framework to predict complex turbulent flow and transition phenomena in high free‐stream turbulence environments of high pressure linear turbines.

This is the first instance in which both artificially modified random flow generation method in association with the dynamic procedure of LES application is employed to represent the realistic inflow turbulence conditions in the high pressure turbine and to resolve the transitional flow in a dynamic approach.

Some recent effort showed that usage of Krueger flaps helps to maintain laminar flow in cruise flight. Such flaps are positioned higher relative to the chord to shield the leading edge from the insect contamination during take-off. The flap passes several through critical intermediate position during the deployment to its design position. The purpose of this paper is to analyse the aerodynamics.

To better understand such flow phenomena, the combined approach of computational fluid dynamics and experimental methods were used. Flow simulation was performed with in-house finite volume Navier–Stokes solver in fully turbulent unsteady RANS regime. The experimental data were obtained by means of force and pressure measurements and some areas of the flow field were examined with 2 C particle image velocimetry.

The airfoil with flap in critical position has a very limited maximum lift coefficient. The maximum achievable lift coefficient during the deployment is significantly affected by the vertical position of the trailing edge of the flap. The most unfavourable position during the deployment is not the flap perpendicular to the chord, but the flap inclined closer to it is the retracted position.

The flap movement was not simulated either in the simulation or in the experiment. Only intermediate static positions were examined.

A better understanding of aerodynamic phenomena connected with the deployment of a Krueger flap can contribute to the simpler and lighter of kinematics and also to decrease time-to-market.

Limited experimental and computational results of Krueger flap in critical positions during the deployment are published in the literature.

In the European project AFLoNext, active flow control (AFC) measures were adopted in the wing tip extension leading edge to suppress flow separation. It is expected that the designed wing tip extension may improve aerodynamic efficiency by about 2 per cent in terms of fuel consumption and emissions. As the leading edge of the wing tip is not protected with high-lift device, flow separation occurs earlier than over the inboard wing in the take-off/landing configuration. The aim of this study is the adoption of AFC to delay wing tip stall and to improve lift-to-drag ratio.

Several actuator locations and AFC strategies were tested with computational fluid dynamics. The first approach was “standard” one with physical modeling of the actuators, and the second one was focused on the volume forcing method. The actuators location and the forcing plane close to separation line of the reference configuration were chose to enhance the flow with steady and pulsed jet blowing. Dependence of the lift-to-drag benefit with respect to injected mass flow is investigated.

The mechanism of flow separation onset is identified as the interaction of slat-end and wing tip vortices. These vortices moving toward each other with increasing angle of attack (AoA) interact and cause the flow separation. AFC is applied to control the slat-end vortex and the inboard movement of the wing tip vortex to suppress their interaction. The separation onset has been postponed by about 2° of AoA; the value of ift-to-drag (L/D) was improved up to 22 per cent for the most beneficial cases.

The AFC using the steady or pulsed blowing (PB) was proved to be an effective tool for delaying the flow separation. Although better values of L/D have been reached using steady blowing, it is also shown that PB case with a duty cycle of 0.5 needs only one half of the mass flow.

Two approaches of different levels of complexity are studied and compared. The first is based on physical modeling of actuator cavities, while the second relies on volume forcing method which does not require detailed actuator modeling. Both approaches give consistent results.

The purpose of this paper devoted to the application of modal analysis to analyze the flow structure of trailing edge cutback film cooling and the effects of vortex structure on the film cooling effectiveness of the cutback surface.

Large eddy simulation (LES) is used to simulate the trailing edge cutback film cooling. The results of LES are analyzed by proper orthogonal decomposition (POD) method and dynamic mode decomposition (DMD) method. The POD method is used to determine the dominated vortex structure and the energy level of these structures. The DMD method is used to analyze the relationship between vortex structures and wall temperature.

The POD method shows that the flow field consists of three main vortices – streamwise vortex, lip vortex and coolant vortex. The DMD results show that the lip vortex mainly acts on the middle section of the cutback surface, while the streamwise vortex mainly acts on the back section of the cutback surface.

The modal analysis is only based on numerical simulation but the modal analysis of experimental results will be further studied in the future.

This paper presents the powerful ability of the modal analysis method to study complex flows in trailing edge cutback film cooling. Establishing the relationship between vortex and wall temperature by modal analysis method can provide a new idea for studying convective heat transfer problems.

The role of streamwise vortex in the flow of the trailing edge cutback cooling and its effect on the cooling effectiveness of the cutback surface is found.

To perform 3D unsteady Reynolds Averaged Navier‐Stokes (URANS) simulations to predict turbulent flow over bluff body.

Turbulence closure is achieved through a non‐linear k−ε model. This model is incorporated in commercial FLUENT software, through user defined functions (UDF).

The study shows that the present URANS with standard wall functions predicts all the major unsteady phenomena, with a good improvement over other URANS reported so far, which incorporate linear eddy viscosity models. The results are also comparable with those obtained by LES for the same test case.

When comparing the computational time required by the present model and by LES, the accuracy achieved is significant and can be used for simulating 3D unsteady complex engineering flows with reasonable success.

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.

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.

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

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

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.

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.

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.

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.

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

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.