Evaluation of flow characteristics that give higher mixing performance in the 3-D T-mixer versus the typical T-mixer

This document is the Accepted Manuscript of the following article: Cesar Augusto Cortes-Quiroz, Alireza Azarbadegan, and Mehrdad Zangeneh, ‘Evaluation of flow characteristics that give higher mixing performance in the 3-D T-mixer versus the typical T-mixer’, Sensors and Actuators B: Chemical, Vol. 202: 1209-1219, October 2014, DOI: https://doi.org/10.1016/j.snb.2014.06.042, made available under the the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License CC BY NC-ND 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).A 3-D configuration of a T-mixer is evaluated under normal operating conditions of the called convective micromixers. The design has been called 3-D T-mixer in our previous work [1] as it adopts a three-dimensional structure at the T-junction. This design feature has been found that it exerts a strong effect on the flow characteristics in the device downstream in the mixing channel. A numerical study has been carried out in the 3-D T-mixer and the typical T-mixer, being these modelled with equal dimensions of channel lengths and cross sections and operated with the same flow rates. The flow analysis in the 3-D T-mixer reveals the quick formation of vortical flow structures composed of intertwined fluid filaments which increase drastically the fluids interface to enhance mixing. The flow patterns in the mixing channel vary with Reynolds number (Re) in the range 100-500. This study shows that the 3-D T-mixer provides a significant enhancement of mixing and presents lower pressure loss and similar level of shear stress compared to a typical T-mixer, in the whole range of Re used to characterize the flow. It has a simple channel configuration which is easy to fabricate and effective for mixing of continuous fluid and potentially particles. The 3-D T-mixer is called to be tested and applied for improving the efficiency of systems which have a T-junction in their design and require fast mixing with high throughput.Peer reviewedFinal Accepted Versio

A robust inverse design solver for controlling the potential aggressiveness of cavitating flow on hydrofoil cascades

This article presents the development of a new inverse design algorithm capable of generating blade geometries for cavitating cascade flows. With this methodology, we demonstrate the controllability of the pressure distribution in and around the cavity and thereby provide a means to regulate the aggressiveness of blade cavitation phenomena. The solver proposed here uses the Tohoku–Ebara equation of state to model phase change, combined with bespoke preconditioning and multigrid methods designed to handle the system's ill conditioning and cope with the hypersonic flow regime of the mixture, respectively. Blade geometries and the cavitating flow field are calculated simultaneously in a robust and efficient manner, with a blade loading that matches the target distribution. In this article, the accuracy of the cavitating flow solver is first demonstrated for the NACA0015 hydrofoil case and associated experimental data. The inverse design procedure is then applied to a typical axial flow pump cascade: a new blade profile is generated with a topology that successfully reduces the gradient of the pressure jump at cavity closure

Numerical analysis of an initial design of a counter-rotating pump-turbine

Renewable sources of energy are on the rise and will continue to increase the coming decades. A common problem with the renewable energy sources is that they rely on effects which cannot be controlled, for instance the strength of the wind or the intensity of the sunlight. The ALPHEUS Horizon 2020 EU project has the aim to develop a low-head hydraulic pump-turbine which can work as a grid stabilising unit. This work presents numerical results of an initial hub-driven counter-rotating pump-turbine design within ALPHEUS. Computational fluid dynamics simulations are carried out in both prototype and model scale, for pump and turbine modes, and under steady-state and unsteady conditions. The results indicate that the initial design have a hydraulic efficiency of roughly 90 % in both modes and for a wide range of operating conditions. The unsteady simulations reveal a complex flow pattern downstream the two runners and frequency analysis show that the dominating pressure pulsations originates from the rotor dynamics. Given the promising high efficiency, this initial design makes an ideal platform to continue the work to optimise efficiency and transient operations further

Experimental analysis of shock smoothing design strategy for reducing cavitation erosion aggressiveness

This article presents the experimental analysis of cavitation erosion for two cascade hydrofoil profiles. The aim is to evaluate the change in erosive intensity between a conventional smooth blade surface and one generated by the means of inverse design specifically to reduce cavitation aggressiveness. The applied design strategy consists in imposing a reduced amplitude and gradient at the cavity closure pressure jump in order to bring down the potential energy contained in the vapor sheet. The result is a unique geometry that presents a surface kink located at cavity closure, which successfully smoothes the pressure jump according to computational fluid dynamics (CFD) verification analysis. Here, an experimental rig is constructed and equipped with a pressure sensing system and high-speed imaging to capture the flow field. The measurements for both geometries are first compared against a set of steady-state CFD solutions, which demonstrate the reliability of the inverse design solver for generating targeted flow characteristics in non-cavitating and cavitating conditions. Visual recordings also reveal significant changes in the aspect of the vapor sheet between the two blades indicating a shift in its dynamic behavior. Erosion intensity levels are then measured by paint method at identical conditions. The outcome of the experiment is highly conclusive as a marked reduction in paint erosion is observed for the design geometry. The measured data also serve as a benchmark test for predictive cavitation erosion models by comparing the measured erosion distributions for each blade to those obtained numerically from unsteady CFD

The contribution of low-head pumped hydro storage to a successful energy transition

The pan-European power grid is experiencing an increasing penetration of Variable Renewable Energy (VRE). The fluctuating and non-dispatchable nature of VRE hinders them in providing the Ancillary Service (AS) needed for the reliability and stability of the grid. Today’s grid is reliant on synchronous generators. In case of sudden frequency deviations, the inertia of their rotating masses contributes significantly to the stabilisation of the system. However, as the modern power grid is gravitating towards an inverter-dominated system, these must also be able to replicate this characteristic. Therefore, Energy Storage Systems (ESS) are needed along the VRE. Among the different ESS, Pumped Hydro Storage (PHS) can be identified as particularly convenient, given its cost-effective implementation and considerable lifespan, in comparison to other technologies. PHS is reliant on difference in altitudes, which makes this technology only available if suitable topographic conditions exist. The ALPHEUS project will introduce a low-head PHS for a relatively flat topography. In this paper, a grid-forming controlled inverter coupled with low-head PHS that can contribute to the grid stability is introduced, emphasising its ability to provide different AS, especially frequency control, through the provision of synthetic system inertia, as well as fast Frequency Containment Reserves (fFCR)

The Contribution of Low-Head Pumped Hydro Storage to a successful Energy Transition

The pan-European power grid is experiencing an increasing penetration of Variable Renewable Energy (VRE). The fluctuating and non-dispatchable nature of VRE hinders them in providing the Ancillary Service (AS) needed for the reliability and stability of the grid. Today’s grid is reliant on synchronous generators. In case of sudden frequency deviations, the inertia of their rotating masses contributes significantly to the stabilisation of the system. However, as the modern power grid is gravitating towards an inverter-dominated system, these must also be able to replicate this characteristic. Therefore, Energy Storage Systems (ESS) are needed along the VRE. Among the different ESS, Pumped Hydro Storage (PHS) can be identified as particularly convenient, given its cost-effective implementation and considerable lifespan, in comparison to other technologies. PHS is reliant on difference in altitudes, which makes this technology only available if suitable topographic conditions exist. The ALPHEUS project will introduce a low-head PHS for a relatively flat topography. In this paper, a grid-forming controlled inverter coupled with low-head PHS that can contribute to the grid stability is introduced, emphasising its ability to provide different AS, especially frequency control, through the provision of synthetic system inertia, as well as fast Frequency Containment Reserves (fFCR)

Three-dimensional design of radial-inflow turbines.

This thesis is not available on this repository until the author agrees to make it public. If you are the author of this thesis and would like to make your work openly available, please contact us: [email protected] Library can supply a digital copy for private research purposes; interested parties should submit the request form here: http://www.lib.cam.ac.uk/collections/departments/digital-content-unit/ordering-imagesPlease note that print copies of theses may be available for consultation in the Cambridge University Library's Manuscript reading room. Admission details are at http://www.lib.cam.ac.uk/collections/departments/manuscripts-university-archive

Multi-Point, Multi-Objective Optimization of Centrifugal Fans by 3D Inverse Design Method

Centrifugal fan stages are used in many applications where relatively high pressure rise is required in compact size. The application can vary from household appliances, industrial to airconditioning and data centre cooling applications. In many of these applications the fan stages are required to meet multi-point requirements in terms of both pressure rise and efficiency. In this paper we present the design of a centrifugal fan stage for multi-point and multi-objective requirements. The paper starts from basic requirements for the design such as pressure rise, flow rate and rpm at 2 operating points. The fan stage needs to meet a maximum torque requirement set by the motor power. An initial flow path for the stage is generated by using a meanline code by using one of these operating points. This meridional geometry is then used in a 3D inverse design method in which the 3D blade geometry of the impeller is generated for a given distribution of loading ( or pressure jump) on the blade. The aim of this initial design is to create a baseline for multi-point optimization. For optimization the meridional geometry of the impeller and inlet nozzle are parametrized. The blade loading is also parametrized on one streamwise location in order to meet the requirements for the blade to be manufactured by a metal pressing process. In total 14 parameters are used for meridional shape and blade shape. By using a wide range of variation of these 14 design parameters and Design of Experiments method a design matrix is generated for about 120 fan geometries. These geometries are then run in steady 3D RANS code for the two operating points. The CFD set up used tries to represent the measurement set up and hence covers a suitably large inblock and outblock boundary. Important objectives such as efficiency, pressure rise and torque are then extracted from the CFD solution at the two operating points. These results are then used together with the design matrix in a surrogate model based Kriging method. A multi-objective Genetic Algorithm (MOGA) is then run on the surrogate model to find trade offs between the efficiency and pressure rise at the two operating points subject to constraints on maximum torque and also slope of the pressure rise change between the two operating points. The design with the best efficiency at the two operating points is then exported from the surrogate model and run in CFD. The CFD results confirm significant improvement in efficiency over the baseline design and also show that the actual CFD values for efficiency, torque and pressure rise at the two operating points are very close that predicted by surrogate model. Hence confirming the accuracy of the surrogate model used for design optimization. This process can be used to speed up the design optimization of centrifugal fan for multiple operating points under industrial time scales