A review of methods for vortex identification in hydroturbines

Zhang, Yuning; Liu, Kaihua; Xian, Haizhen; Du, Xiaoze

doi:10.1016/j.rser.2017.05.058

Cited by 207 publications

(68 citation statements)

References 62 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Therefore, the vortices have to be identified using a suitable criterion. Among the criteria suggested in [9], an iso-surface of Q-criterion has been used to identify coherent vortices, because this criterion is particularly adapted to the identification of large scale vortices in a turbulent flow.…”

Section: Validation Of the Modelmentioning

confidence: 99%

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Doussot¹,

Balarac²,

Brammer³

et al. 2020

IJFMS

View full text Add to dashboard Cite

Hydraulic machines are designed to operate in flow conditions close to the best efficiency point. However, to respond to the increasing demand for flexibility mainly due to the integration of renewable energy in the electric grid, the operating range of Francis turbines has to be extended towards smaller discharge levels without restriction. When Francis turbines are operated typically between 30% and 60% of the rated output power, the flow field is characterized by the appearance of inter-blade vortices in the runner. In these off-design operating conditions and due to these phenomena, dynamic stresses level can increase, and potentially lead to fatigue damage of the mechanical structure of the machine. The objective of this paper is to present investigations on the dynamic behaviour of the inter-blade vortices and their impact on the runner by using numerical simulations. Computations were performed with different turbulence modelling approaches to assess their relevance and reliability: Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES). Computations aimed to better understand the emergence condition of the inter-blade vortices. The analysis showed that vortices can be generated due to poor inlet adaptation at part load, however other vortices can also be due to a local backflow in the runner. The competition between these both phenomena leads to various topologies of the inter-blade vortices. The numerical results were compared to experimental visualizations performed on scaled model as well as to previous numerical studies results. The impact of these inter-blade vortices on the runner were also investigated by considering the pressure fluctuations induced on the blades. The dynamic loading on the blade has to be known in order to evaluate the lifetime of the runner by mechanical analysis. Different operating conditions have been simulated to understand how the pressure fluctuations depend on the operating conditions. The localization of the pressure fluctuations and their consequences on the frequency signature of the torque fluctuations have been analyzed. This article is presenting a part of the work presented at the 29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, 2018 [1], and presents another vortex topology and a comparison of LES results of several operating conditions.

show abstract

Section: Validation Of the Modelmentioning

confidence: 99%

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Doussot¹,

Balarac²,

Brammer³

et al. 2020

IJFMS

View full text Add to dashboard Cite

show abstract

“…where (45) tr tr (46) det (47) , and are three invariants. For incompressible flow, according to continuous equation, we have 0.…”

Section: A Eigenvalue-based Criteriamentioning

confidence: 99%

Rortex and comparison with eigenvalue-based vortex identification criteria

2018

View full text Add to dashboard Cite

Most of the current Eulerian vortex identification criteria, including the Q criterion and the criterion, are exclusively determined by the eigenvalues of the velocity gradient tensor or the related invariants and thereby can be regarded as eigenvaluebased criteria. However, these criteria will be plagued with two shortcomings: (1) these criteria fail to identify the swirl axis or orientation;(2) these criteria are prone to severe contamination by shearing. To address these issues, a new vector named Rortex which represents the local fluid rotation was proposed in our previous work. In this paper, an alternative eigenvector-based definition of Rortex is introduced. The direction of Rortex, which represents the possible axis of the local rotation, is determined by the real eigenvector of the velocity gradient tensor. And then the rotational strength obtained in the plane perpendicular to the possible axis is used to define the magnitude of Rortex.This new equivalent definition allows a much more efficient implementation.Furthermore, a systematic interpretation of scalar, vector and tensor versions of Rortex is presented. By relying on the tensor interpretation, the velocity gradient tensor is decomposed to a rigid rotation part and a non-rotational part including shearing, stretching and compression, different from the traditional symmetric and antisymmetric tensor decomposition. It can be observed that shearing always manifests its effect on the imaginary part of the complex eigenvalues and consequently contaminates eigenvalue-based criteria, while Rortex can exclude the shearing contamination and accurately quantify the local rotational strength. In addition, in contrast to eigenvaluebased criteria, not only the iso-surface of Rortex, but also the Rortex vectors and the Rortex lines can be applied to investigate vortical structures. Several comparative

show abstract

“…According to the previous research, the ice mainly accretes on the blade surface of wind turbines [8][9][10]. This will affect the aerodynamic and load distribution, which will decrease the power performance and threaten the safety of wind turbines [11][12][13]. Therefore, it is essential to research ice accretion on blade surfaces of wind turbines [14,15].…”

Section: Introductionmentioning

confidence: 99%

Scaling Method of the Rotating Blade of a Wind Turbine for a Rime Ice Wind Tunnel Test

Sun

Jiang

et al. 2019

Energies

View full text Add to dashboard Cite

In order to research the law of rime ice accretion on different scaling blades surface, a new rime ice scaling method was proposed in this research. According to previous research, there are three kinds of ice types on blade surfaces: rime ice, glaze ice and mixed ice. Under the condition of rime ice, both the freezing fraction and the coefficient of heat transfer between super-cold water droplets and blade are 100%. The heat transfer model of rime ice is simpler than that of glaze ice and mixed ice. In this research, the scaling parameters including flow field, water droplets, temperature, pressure and rotating parameters were defined. The Weber number (We) based on water film thickness as an important parameter was applied in this study. The rotating parameters including rotating speed and radius had been added into the icing scaling method. To verify the effectiveness of the new rime ice scaling method, icing wind tunnel tests were carried out. The NACA0018 airfoil was used for the test blade. Two kinds of scale chord blades were selected, the chord of full-scale blade was 200 mm and of subscale blade was 100 mm. The test temperature was −15 °C. The ice accretion on different scale blades surface were captured by high-speed camera and the icing shapes of different scaling blades were obtained. To quantitatively analyze the similar degree of icing shapes on different scale blades, an evaluation method which included similar degree (Sim) was established based on the typical characteristic parameters proposed by previous research. The results show that the icing shapes of subscale blades are similar to that of full-scale blades. The similar degree is between 75.22% and 93.01%. The icing wind tunnel test indicates that the new rime ice scaling method is an effective method to study the rime ice of large scale rotating blades. This study can be used as a reference for research on anti-icing and de-icing technologies for large-scale HAWTs (Horizontal Axis Wind Turbines).

show abstract

A review of methods for vortex identification in hydroturbines

Cited by 207 publications

References 62 publications

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

Rortex and comparison with eigenvalue-based vortex identification criteria

Scaling Method of the Rotating Blade of a Wind Turbine for a Rime Ice Wind Tunnel Test

Contact Info

Product

Resources

About