Claire Deschênes

Flow simulation and efficiency hill chart prediction for a Propeller turbine

In the present paper, we focus on the flow computation of a low head Propeller turbine at a wide range of design and off-design operating conditions. First, we will present the results on the efficiency hill chart prediction of the Propeller turbine and discuss the consequences of using non-homologous blade geometries for the CFD simulation. The flow characteristics of the entire turbine will be also investigated and compared with experimental data at different measurement planes. Two operating conditions are selected, the first one at the best efficiency point and the second one at part load condition. At the same time, for the same selected operating points, the numerical results for the entire turbine simulation will be compared with flow simulation with our standard stage calculation approach which includes only guide vane, runner and draft tube geometries.

Academic Mentoring and Dropout Prevention for Students in Math, Science and Technology

In this study, we examined the impact of a new academic mentoring program aimed at preventing student dropout in math, science and technology. The MIRES program entails bimonthly meetings between students entering college and university students completing their undergraduate degree in science and engineering. A randomized pretest-posttest control group design was used to evaluate the program’s short-term impact. At the end of the program, mentees (n = 150) presented significantly higher levels of motivation, a more positive career decision profile and enhanced institutional attachment and social adjustment than students in the control group (n = 157). MIRES mentees also showed success and persistence rates (mainly male participants) that were significantly higher than those of students in the control group.

Numerical prediction of a bulb turbine performance hill chart through RANS simulations

Within the framework of an international research consortium on low-head hydraulic turbine flow dynamics, the predictive behavior of Reynolds Averaged Navier-Stokes (RANS) simulations of the efficiency (η) hill chart of a bulb turbine is investigated. The paper presents the impacts of the blade tip gap and the hub gaps on performance predictions.

A finite element formulation of compressible flows using various sets of independent variables

Abstract This paper presents a finite element method for the simulation of compressible flows. The Navier–Stokes and Euler equations are solved in the conservation form using various sets of independent variables. A variational formulation is developed based upon a variant of the Petrov–Galerkin method, and uses a shock-capturing operator. An adaptive algorithm based on a particular residual norm is proposed. Several numerical examples are presented to demonstrate the performances of each set of variables in solving compressible high-speed flows.

Draft tube flow phenomena across the bulb turbine hill chart

In the framework of the BulbT project launched by the Consortium on Hydraulic Machines and the LAMH (Hydraulic Machine Laboratory of Laval University) in 2011, an intensive campaign to identify flow phenomena in the draft tube of a model bulb turbine has been done. A special focus was put on the draft tube component since it has a particular importance for recuperation in low head turbines. Particular operating points were chosen to analyse flow phenomena in this component. For each of these operating points, power, efficiency and pressure were measured following the IEC 60193 standard. Visualizations, unsteady wall pressure and efficiency measurements were performed in this component. The unsteady wall pressure was monitored at seven locations in the draft tube. The frequency content of each pressure signal was analyzed in order to characterize the flow phenomena across the efficiency hill chart. Visualizations were recorded with a high speed camera using tufts and cavitation bubbles as markers. The predominant detected phenomena were mapped and categorized in relation to the efficiency hill charts obtained for three runner blade openings. At partial load, the vortex rope was detected and characterized. An inflection in the partial load efficiency curves was found to be related to complex vortex rope instabilities. For overload conditions, the efficiency curves present a sharp drop after the best efficiency point, corresponding to an inflection on the power curves. This break off is more severe towards the highest blade openings. It is correlated to a flow separation at the wall of the draft tube. Also, due to the separation occurring in these conditions, a hysteresis effect was observed on the efficiency curves.

Experimental Investigation of Draft Tube Inlet Velocity Field of a Propeller Turbine

The draft tube of reaction hydraulic turbines is subject to numerous investigations since it accounts for a significant portion of the energy recovery. But even with up-to-date computational fluid dynamics methodologies, simulating the draft tube flow remains highly challenging since it is a diverging swirling flow that may undergo flow separations and become dominated by unsteady secondary flows. Within the framework of a collaborative research project on the flow dynamics of a propeller turbine model, the flow at the inlet region of the draft tube was studied using 2D-laser Doppler velocimetry (2D-LDV). Measurements were used to detect and characterize the flow structures at three operating conditions: partial discharge, near best efficiency, and full-load conditions. The paper presents analysis based on phased-averaged velocity fields to yield information on fluctuations and dominant frequencies according to runner positions. The main features detected are the flow nonuniformity at the runner exit and the secondary flow structures associated with the runner hub wake. Those results are part of a larger database aimed at providing test cases for the validation of numerical simulation strategies.

Modern challenges for flow investigations in model hydraulic turbines on classical test rig

The BulbT project involved several investigations of flow phenomena in different parts of a model bulb turbine installed on the test rig of Laval University Laboratory. The aim is to create a comprehensive data base in order to increase the knowledge of the flow phenomena in this type of turbines and to validate or improve numerical flow simulation strategies. This validation being based on a kinematic comparison between experimental and numerical data, the project had to overcome challenges to facilitate the use of the experimental data for that purpose. Many parameters were checked, such as the test bench repeatability, the intrusiveness of a priori non-intrusive methods, the geometry of the runner and draft tube. This paper illustrates how some of those problematic were solved.

Monitoring of velocity and pressure fields within an axial turbine

In the framework of the consortium of R&D on hydraulic machines launched by the LAMH (Hydraulic Machines Laboratory of Laval University) in November 2007, a five holes unsteady pressure probe using embedded pressure sensors has been developed. Such probe allows us to obtain the unsteady static pressure, total pressure and the three flow velocity components. This paper aims to present this new five holes unsteady pressure probe, used and results for a propeller turbine.

Numerical and Experimental Investigation of Rotor-Stator Interactions in an Axial Turbine: Numerical Interface Assessment

In this paper, the rotor-stator interaction in an axial hydraulic turbine is studied with the help of a 2D test case and validation with experimental data. The computational method is presented in the first part of the paper along with the results from the shedding flow behind a square cylinder to investigate a numerical interface between non-matching meshes. The turbulent kinetic energy budget and the centerline velocity past the interface are analyzed and compared with literature. In the second part of the paper, knowledge gained from the 2D test case is applied to 3D simulation of a hydraulic turbine model. Potential interactions are studied using FFT of the time signal on different positions upstream and downstream of a sliding mesh interface. The wake dissipation is investigated for several meridional positions downstream of the turbine guide vanes. The numerical flow field is compared against 2D-LDV experimental measurements at the runner outlet. Numerical results are in good agreement with experimental data.Copyright

Experimental investigation of the draft tube inlet flow of a bulb turbine

In the BulbT project framework, a bulb turbine model was studied with a strongly diverging draft tube. At high discharge, flow separation occurs in the draft tube correlated to significant efficiency and power drops. In this context, a focus was put on the draft tube inlet flow conditions. Actually, a precise inlet flow velocity field is required for comparison and validation purposes with CFD simulation. This paper presents different laser Doppler velocimetry (LDV) measurements at the draft tube inlet and their analysis. The LDV was setup to measure the axial and circumferential velocity on a radius under the runner and a diameter under the hub. A method was developed to perform indirect measurement of the mean radial velocity component. Five operating conditions were studied to correlate the inlet flow to the separation in the draft tube. Mean velocities, fluctuations and frequencies allowed characterizing the flow. Using this experimental database, the flow structure was characterized. Phase averaged velocities based on the runner position allowed detecting the runner blade wakes. The velocity gradients induced by the blade tip vortices were captured. The guide vane wakes was also detected at the draft tube inlet. The recirculation in the hub wake was observed.