Staggered Array Configuration Research Articles

Tidal turbine array modelling using goal-oriented mesh adaptation

To examine the accuracy and sensitivity of tidal array performance assessment by numerical techniques applying goal-oriented mesh adaptation. The goal-oriented framework is designed to give rise to adaptive meshes upon which a given diagnostic quantity of interest (QoI) can be accurately captured, whilst maintaining a low overall computational cost. We seek to improve the accuracy of the discontinuous Galerkin method applied to a depth-averaged shallow water model of a tidal energy farm, where turbines are represented using a drag parametrisation and the energy output is specified as the QoI. Two goal-oriented adaptation strategies are considered, which give rise to meshes with isotropic and anisotropic elements. We present both fixed mesh and goal-oriented adaptive mesh simulations for an established test case involving an idealised tidal turbine array positioned in a channel. With both the fixed meshes and the goal-oriented methodologies, we reproduce results from the literature which demonstrate how a staggered array configuration extracts more energy than an aligned array. We also make detailed qualitative and quantitative comparisons between the fixed mesh and adaptive outputs. The proposed goal-oriented mesh adaptation strategies are validated for the purposes of tidal energy resource assessment. Using only a tenth of the number of degrees of freedom as a high-resolution fixed mesh benchmark and lower overall runtime, they are shown to enable energy output differences smaller than 2% for a tidal array test case with aligned rows of turbines and less than 10% for a staggered array configuration.

Thermal Performance of Double-Sided, Partial Height Strip Fin Arrays in a High Aspect Ratio, Rectangular Channel

Abstract Friction loss and heat transfer enhancement measurements were obtained for double-sided, partial height, strip fin arrays in a high aspect ratio (AR = 8), rectangular channel. Fins were arranged in a staggered array configuration with channel height to fin thickness ratio H/W = 9.6, spanwise spacing distance to fin thickness ratio S/W = 8.0, and streamwise spacing distance to fin length ratio X/L = 1.0. Within the channel, shortened strip fins of equal length are positioned directly opposite to each other on two heat transfer surfaces with three gap size to channel height ratios considered G/H = 0.2, 0.3, and 0.4, respectively. The thermal performance of each fin configuration is determined from the measured pressure drop across the array and regionally averaged heat transfer coefficients at flow Reynolds numbers ranging Re = 20,000–80,000. Partial height strip fin results are compared to the baseline cases of full height strip fins and the smooth channel. Correlations of friction loss, heat transfer enhancement, and thermal performance are provided as functions of flow Reynolds numbers for all cases. Full height strip fins provide the greatest heat transfer enhancement of all cases but introducing a gap size can significantly reduce friction losses. The thermal performance is greatest when using full height strip fins for Reynolds numbers ranging Re = 20,000–30,000 and using partial height strip fins with the gap size of G/H = 0.3 for Re = 40,000–80,000.

Optimization study of solar farm layout for concentrator photovoltaic system on azimuth-elevation sun-tracker

Inappropriate space allocation for concentrator photovoltaic (CPV) systems in the solar farm causes optical losses via shadowing between adjacent CPV systems, which leads to the deterioration of the overall electrical generation of solar power plant (SPP). The deterioration of the overall electrical generation can be reduced by increasing the separation distance between adjacent CPV systems. However, it causes an increase in land-related costs due to ineffectiveness in land utilization. Therefore, it is important to focus on the layout design optimization in the SPP to attain the best trade-off between land usage and energy generation. In order to captivate the interest of investors in the future development of solar energy, levelized cost of electricity (LCOE) of the SPP needs to be competitive. A newly developed computational algorithm has been introduced to perform the optimization of the CPV field layout system by utilizing the local weather data with the consideration of shadowing effect, edge effect, land aspect ratio (LAR) and land cost. A case study has been conducted in Kota Kinabalu, Malaysia to evaluate the performance of CPV system in the SPP based on different conditions such as Dew/L ratio, Dns/L ratio, spacing angle, LAR and land cost for both square array and staggered array configuration. From the case study, the results show that the optimized field layout for the CPV systems for LAR of 1 is a staggered array layout configuration with Dew/L ratio of 2.50 at spacing angle of 45°, which accommodates the lowest value of LCOE.

Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array

Tidal stream turbines are subject to complex flow conditions, particularly when installed in staggered array configurations where the downstream turbines are affected by the wake and/or bypass flow of upstream turbines. This work presents, for the first time, methods for and results from the physical testing of three 1/15 scale instrumented turbines configured in a closely-spaced staggered array, and demonstrates experimentally that increased power extraction can be achieved through reduced array separation. A comprehensive set of flow measurements was taken during several weeks testing in the FloWave Ocean Energy Research Facility, with different configurations of turbines installed in the tank in a current of 0.8 m/s, to understand the effect that the front turbines have on flow through the array and on the inflow to the centrally placed rearmost turbine. Loads on the turbine structure, rotor, and blade roots were measured along with the rotational speed of the rotor to assess concurrently in real-time the effects of flow and array geometry on structural loading and performance. Operating in this closely-spaced array was found to improve the power delivered by the rear turbine by 5.7–10.4% with a corresponding increase in the thrust loading on the rotor of 4.8–7.3% around the peak power operating point. The experimental methods developed and results arising from this work will also be useful for further scale-testing elsewhere, validating numerical models, and for understanding the performance and loading of full-scale tidal stream turbines in arrays.

Analyzing the Near-Field Effects and the Power Production of an Array of Heaving Cylindrical WECs and OSWECs Using a Coupled Hydrodynamic-PTO Model

The Power Take-Off (PTO) system is the key component of a Wave Energy Converter (WEC) that distinguishes it from a simple floating body because the uptake of the energy by the PTO system modifies the wave field surrounding the WEC. Consequently, the choice of a proper PTO model of a WEC is a key factor in the accuracy of a numerical model that serves to validate the economic impact of a wave energy project. Simultaneously, the given numerical model needs to simulate many WEC units operating in close proximity in a WEC farm, as such conglomerations are seen by the wave energy industry as the path to economic viability. A balance must therefore be struck between an accurate PTO model and the numerical cost of running it for various WEC farm configurations to test the viability of any given WEC farm project. Because hydrodynamic interaction between the WECs in a farm modifies the incoming wave field, both the power output of a WEC farm and the surface elevations in the ‘near field’ area will be affected. For certain types of WECs, namely heaving cylindrical WECs, the PTO system strongly modifies the motion of the WECs. Consequently, the choice of a PTO system affects both the power production and the surface elevations in the ‘near field’ of a WEC farm. In this paper, we investigate the effect of a PTO system for a small wave farm that we term ‘WEC array’ of 5 WECs of two types: a heaving cylindrical WEC and an Oscillating Surge Wave Energy Converter (OSWEC). These WECs are positioned in a staggered array configuration designed to extract the maximum power from the incident waves. The PTO system is modelled in WEC-Sim, a purpose-built WEC dynamics simulator. The PTO system is coupled to the open-source wave structure interaction solver NEMOH to calculate the average wave field η in the ‘near-field’. Using a WEC-specific novel PTO system model, the effect of a hydraulic PTO system on the WEC array power production and the near-field is compared to that of a linear PTO system. Results are given for a series of regular wave conditions for a single WEC and subsequently extended to a 5-WEC array. We demonstrate the quantitative and qualitative differences in the power and the ‘near-field’ effects between a 5-heaving cylindrical WEC array and a 5-OSWEC array. Furthermore, we show that modeling a hydraulic PTO system as a linear PTO system in the case of a heaving cylindrical WEC leads to considerable inaccuracies in the calculation of average absorbed power, but not in the near-field surface elevations. Yet, in the case of an OSWEC, a hydraulic PTO system cannot be reduced to a linear PTO coefficient without introducing substantial inaccuracies into both the array power output and the near-field effects. We discuss the implications of our results compared to previous research on WEC arrays which used simplified linear coefficients as a proxy for PTO systems.

Experimental study of wake characteristics in tidal turbine arrays

Abstract For the successful deployment of large scale tidal turbine arrays occupying a large part of tidal channels, understanding the effects of wake interaction in densely spaced arrays is of importance. A comprehensive set of experiments has been conducted with scaled tidal turbines to investigate the resulting wake characteristics in a number of different staggered array configurations with up to four turbines on a designated support frame. Wake velocity deficits and turbulence intensities at a number of locations within and downstream of the array are presented and in addition the flow field recordings from Particle Image Velocimetry (PIV) measurements are presented for visual investigation of the resulting wake field and wake characteristics along the array centre line. The experiments show that lateral and longitudinal spacing variations of the individual devices vary the resulting flow field downstream of the array section significantly. Lateral spacing can be optimised to result in beneficial flow effects that accelerate the downstream wake recovery. Very close spacing however leads to significantly reduced velocity recovery. Longitudinal spacing shows less significant influence, especially for configurations with wide lateral distances. Differences in wake velocity deficit of up to 10% have been identified and suggest array wake recovery in and downstream of staggered sections, in areas of lower ambient turbulence levels, to be more significantly influenced by the lateral spacing especially towards the front rows of the array. With every additional array section the increasing turbulence intensity within the array is anticipated to reduce this effect.

CFD AND CONJUGATE HEAT TRANSFER ANALYSIS OF HEAT SINKS WITH DIFFERENT FIN GEOMETRIES SUBJECTED TO FOCED CONVECTION USED IN ELECTRONICS COOLING

Heat sinks are commonly used for cooling of electronic devices. Heat sinks, an array of heat fins, remove the heat from the surfaces of the chips by enhancing the heat Transfer rate through heat conduction process. Heat can also be removed from the chip surfaces through forced convection heat transfer. In this project work, CFD and conjugate heat transfer analysis is carried out for various fin geometries with Zigzag, Fluted, Slanted mirror, Custom pin fin and staggered array configurations for low thermal resistance and minimum pressure drop. Numerical simulations are carried out for each of the above mentioned fin geometries with common base plate thickness of 2 mm, fin height of 28 mm and fin thickness of 1 mm for three different heat loads namely 50 W, 75 W and 100 W with air flow of 3.933 m/s (15 ft3/min or 15 CFM) and air inlet temperature of 25 o C. The results are compared for thermal performance of a heat sink for each of above geometries and it is observe that the fin with Slanted Mirror geometry gives the best performance among all the other geometries for minimum Pressure drop. The average heat transfer coefficients for fins with slanted mirror geometry, zig zag configuration, fluted type, custom pin fin and staggered array are found to be 215 W/m2K, 164 W/m2K, 164 W/m2K, 157 W/m2K and 145 W/m2K respectively

Atmospheric flow and dispersion through arrays of obstacles

Field experiments have been conducted to investigate flow and dispersion through obstacle arrays. Model obstacles which represent real structures at a nominal scale between 1/10 and 1/20 were used. The main purpose of the experiments was to examine flow and dispersion of contaminants in the vicinity of individual obstacles embedded in an array of cubes. Two array configurations were used, namely the in-line and staggered array configurations. The field experiments were supported by flow visualisation trials performed in the wind tunnel. In the light of the results of these wind tunnel trials, the field experiments were carried out using an array spacing S/H = 1.5 (where S is the space between two consecutive array elements). Dispersion around an isolated model building has already been investigated in the field (Mavroidis and Griffiths, 1996). Thus comparison is allowed between dispersion around an isolated obstacle and around the same obstacle embedded in an array of cubes.

Effects of Pin Detached Space on Heat Transfer and Pin-Fin Arrays

Heat transfer and pressure characteristics in a rectangular channel with pin-fin arrays of partial detachment from one of the endwalls have been experimentally studied. The overall channel geometry (W = 76.2 mm, E = 25.4 mm) simulates an internal cooling passage of wide aspect ratio (3:1) in a gas turbine airfoil. With a given pin diameter, D = 6.35 mm = ¼E, three different pin-fin height-to-diameter ratios, H/D = 4, 3, and 2, were examined. Each of these three cases corresponds to a specific pin array geometry of detachment spacing (C) between the pin tip and one of the endwalls, i.e., C/D = 0, 1, 2, respectively. The Reynolds number, based on the hydraulic diameter of the unobstructed cross-section and the mean bulk velocity, ranges from 10,000 to 25,000. The experiment employs a hybrid technique based on transient liquid crystal imaging to obtain the distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. Experimental results reveal that the presence of a detached space between the pin tip and the endwall has a significant effect on the convective heat transfer and pressure loss in the channel. The presence of pin-to-endwall spacing promotes wall-flow interaction, generates additional separated shear layers, and augments turbulent transport. In general, an increase in detached spacing, or C/D, leads to lower heat transfer enhancement and pressure drop. However, C/D = 1, i.e., H/D = 3, of a staggered array configuration exhibits the highest heat transfer enhancement, followed by the cases of C/D = 0 and C/D = 2, i.e., H/D = 4 or 2, respectively.

An experimental method for evaluating the heat transfer coefficient of liquid-cooled short pin fins using infrared thermography

The aim of this research is to evaluate the convective heat transfer coefficient of liquid cooled short pin fins by means of the infrared thermography. An experimental apparatus was set-up to analyze single, in-line and staggered array configurations of short pin fins. In this work the attention is focused on single pins having different shapes: circular, square, triangular and rhomboidal. The infrared thermography is used to indirectly measure the lateral pin temperature by observing the upper surface temperature of radially heated pins; these are placed in a test section chamber equipped with a Zinc Selenide infrared window. Flow visualizations by means of ink tracers are also carried out to relate the thermal behavior with the flow field. Regressions by the Zukauskas correlation were performed for each shape and new coefficients were carried out; a comparison among the different pin geometries underlines a better thermal exchange for the triangular and rhomboidal pins.