Sahan Wasala | Trinity College Dublin (original) (raw)

Papers by Sahan Wasala

NOISE-CON ... proceedings, Nov 29, 2023

2023 29th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)

IEEE Transactions on Components, Packaging and Manufacturing Technology

This study aims to complete and validate a recently developed reduced-order model for the fast pr... more This study aims to complete and validate a recently developed reduced-order model for the fast prediction of aerodynamic performance (P-Q) curve of electronics cooling fans, taking into account the real fan geometry and the tip clearance effect. The effect of tip clearance on tip vortex generation and fan performance was revealed by an experimentally validated 3D computational fluid dynamics (CFD) method. Six different tip clearance ratios ranging from 0% to 12.7% were investigated. The tip clearance was found to have a strong effect on tip vortex generation, which significantly affects the aerodynamic performance of the fan. Fan efficiency increased by up to 7% by reducing the tip clearance ratio by 2.5%. The tip clearance effect was successfully included by the analytical method combined with a correlation equation developed based on the CFD study. The results show that the combined reduced-order model can produce reasonably accurate predictions for fan P-Q curve with errors less than 7.1% compared to CFD results, while having a wide valid range of tip clearance ratio up to 10%. The precision of this model was further validated against experimental results for eight commercial fans. The computational speed of this model is more than three orders of magnitude faster than a steady-state CFD study, making it highly appropriate for fast analysis of fan performance and thermal-flow co-design. Index Terms-Electronics cooling, fan curve, blade element theory, tip clearance, tip vortex. I. INTRODUCTION F ORCED air cooling continues to play an essential role in modern electronics, where high-power density devices and enclosures generate heat that must be dissipated [1]. Electronics cooling fans are widely used in various industrial applications, such as information technology, telecom, automotive, and aerospace [2]. However, with the continuing trend towards compact packaging and high-density thermal management, fan energy consumption and acoustic noise emission are becoming a critical concern for these applications [3]-[5]. Therefore, improving cooling efficiency and reducing fan noise are crucial to extending the life of air-cooling systems [6]. The aerodynamic characteristics of a fan are crucial information for designing and optimising air-cooling systems. Fan manufacturers typically provide this information based on a standardised testing method, consisting of several fan curves that describe the relationship between static pressure, power demand, speed, and efficiency values as a function of Manuscript received xx; revised xx.

INTER-NOISE and NOISE-CON Congress and Conference Proceedings

Axial cooling fans are widely used in data center dense Hard Disk Drive (HDD) storage systems. Ho... more Axial cooling fans are widely used in data center dense Hard Disk Drive (HDD) storage systems. However, these fans emit high noise levels and degrade HDD performance at certain frequencies. Flow at the fan's inlet can be highly turbulent due to the wake generated by fan components such as struts, finger guards, stators/guide vanes, shrouds, and other external system components such as connectors and mounts, power cables and components, circuits etc. The wake-fan interaction also causes high tonal noise. Therefore a proper understanding of this noise mechanism will help optimize the cooling system in next-generation high-performance HDD enclosure systems. This paper focuses on studying this phenomenon using numerical simulations of a typical data center cooling fan combined with various simplified strut geometries as the obstacle. The high-fidelity Computational Fluid Dynamic (CFD) method, Large Eddy Simulation (LES), was used to obtain a transient flow field. The Ffowcs-Williams...

2022 28th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)

48th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2019 MADRID, Madrid, 2019

Aeroacoustic noise, generated by aircraft landing gears during the take-off or landing manoeuvres... more Aeroacoustic noise, generated by aircraft landing gears during the take-off or landing manoeuvres, is considered excessive, causing environmental concerns for the people living close to airports. Therefore, there is an increasing need to innovate new technologies to reduce landing gear noise. For noise reduction, it is primarily important to understand the mechanism of flow-induced landing-gear noise generation and, further, to adapt relevant new technologies to the system in order to reduce noise levels by means of effective manipulation of related aerodynamic flow features. Dielectric Barrier Discharge (DBD) plasma actuators have shown efficiency to control flow separation from bluff bodies, consequently, mitigating subsequent vortex motions and noise generation. In the present paper, a simplified landing-gear model represented by a tandem-cylinders configuration has been used. The airflow has been simulated using hybrid RANS/LES. Effects of the plasma actuation are modelled using two different models. These include the Suzen & Huang model, which solves for the electric field and charge density fields in order to obtain the body force, and the Greenblatt model, which simply assumes that the body force decays exponentially both downstream and normal to the actuator

25th AIAA/CEAS Aeroacoustics Conference, 2019

Airframe is considered to be one of the primary noise sources during aircraft take off and landin... more Airframe is considered to be one of the primary noise sources during aircraft take off and landing maneuvers, causing disturbance to the people living vicinity to airports. With the increasing demand for air transportation, there is need to innovate new technologies to reduce airframe noise. High lift device noise, in particular the wing-flap noise, gives a considerable contribution to the total airframe noise levels. This paper investigates the noise from a simplified wing-flap configuration and possibility of reducing the noise with the use of a Dielectric Barrier Discharge (DBD) plasma actuator. A compressible SST k-ω based Improved Delayed Detached Eddy Simulation (IDDES) has been used to simulate the unsteady flow field. The Ffowcs-Williams & Hawkings (FW-H) acoustic analogy has been used to predict the far field noise. The effects of plasma has been modeled as volumetric body force source, based on the Suzen and Huang model. Results indicate a noise reduction of about 2.5 dB at frequencies below 1 kHz, as electric potential increases to 20 kV. Nomenclature C p = pressure coefficient C Pr ms = coefficient of pressure fluctuations C f lap = chord of the flap [m] C wing = chord of the wing [m] ∆t = time step [s] ì E = electric field [N/C] ì f b = body force vector due to plasma [N/m 3 ] ρ c = charge density [C/m 3 ]

Noise is one of the main reasons for public objection to new wind farm projects. Aeroacoustic noi... more Noise is one of the main reasons for public objection to new wind farm projects. Aeroacoustic noise has been identified as the main noise generation mechanism from wind turbines. Studies show that trailing edge noise is the major noise source from an aerofoil. However, in a highly turbulent environment, leading edge sources could contribute to the far field noise significantly. Therefore it is important to precisely identify the significance noise sources and their distribution. A geometric improvement to the blade shapes could lead to reduction in noise generation. A numerical noise prediction model using an annular section of a wind turbine blade is validated in the present work. The same model is then used to simulate a modified blade geometry. Far field noise results are presented showing noise reduction for the modified blade.

Noise disturbance is one of the major factors considered in the development of wind farms near ur... more Noise disturbance is one of the major factors considered in the development of wind farms near urban areas, and therefore an accurate estimate of the noise levels generated by wind turbines is required before production and installation. Horizontal-axis wind turbines are the most popular type of turbines and the aeroacoustic noise generated by their rotating blades is known to be their most significant source of noise. The region of the turbine blade that produces the strongest acoustic sources has been identified in published acoustic camera measurements and is the 75% – 95% region of blade span. In the present work, a Large Eddy Simulation (LES) of this region is carried out using an annular computational domain, which leads to a significant reduction of computational expense compared to full blade simulations. The Ffowcs Williams and Hawkings (FWH) acoustic analogy is then used to predict the far field sound. Numerical results for a simulation of the CART-2 wind turbine show good...

Noise disturbance from wind turbines is one of the major factors which slows wind farm developmen... more Noise disturbance from wind turbines is one of the major factors which slows wind farm development near populated areas. Therefore, it is important to have an accurate estimate of the noise generated before production and installation of wind turbines. Large Eddy Simulation (LES) can be used to determine the aerodynamic sound produced by a moving surface, but LES of a whole wind turbine is computationally expensive. However, Oerlemans' field measurements show that most of the noise from wind turbines is generated at 75%-95% of the span of the blade. This suggests that simulation of a section with the most significant noise sources could lead to a useful overall noise estimate in the far field. The present work is focused on noise prediction from a wind turbine using a rotational annulus containing a section of a wind turbine blade, which leads to a significant reduction of computational expense. LES with the Ffowcs-Williams and Hawkings acoustic analogy is used to predict the far field acoustic noise. Initial results with rotational CART-2 wind turbine blade show good agreement with the available experimental data.

Airframe is considered to be one of the primary noise sources during aircraft take off and landin... more Airframe is considered to be one of the primary noise sources during aircraft take off and landing maneuvers, causing disturbance to the people living vicinity to airports. With the increasing demand for air transportation, there is need to innovate new technologies to reduce airframe noise. High lift device noise, in particular the wing-flap noise, gives a considerable contribution to the total airframe noise levels. This paper investigates the noise from a simplified wing-flap configuration and possibility of reducing the noise with the use of a Dielectric Barrier Discharge (DBD) plasma actuator. A compressible SST k- based Improved Delayed Detached Eddy Simulation (IDDES) has been used to simulate the unsteady flow field. The Ffowcs-Williams and Hawkings (FW-H) acoustic analogy has been used to predict the far field noise. The effects of plasma has been modeled as volumetric body force source, based on the Suzen and Huang model. Results indicate a noise reduction of about 2.5 dB ...

INTER-NOISE and NOISE-CON Congress and Conference Proceedings

Hard Disk Drive (HDD) system enclosures in a data center require effective cooling systems to avo... more Hard Disk Drive (HDD) system enclosures in a data center require effective cooling systems to avoid HDD overheating. These systems often rely on air cooling because of their cost effciency and maintainability. Air cooling systems typically consist of an array of axial fans which push or pull the air through the system. These fans emit high level tonal noise particularly at high tip speed ratios. High-capacity HDDs, on the other hand, are sensitive to high acoustic noise, which consequently increases the risk of read/write error and deteriorates drive performance. Therefore, cooling fan noise adversely affects the function of the HDD enclosure systems which emphasizes the need to understand the noise sources and develop methods to mitigate HDD noise exposure.

Acoustics, Apr 1, 2020

The interaction of a turbulent flow with the leading edge of a blade is a main noise source mecha... more The interaction of a turbulent flow with the leading edge of a blade is a main noise source mechanism for fans and wind turbines. Motivated by the silent flight of owls, the present paper describes an experimental study performed to explore the noise-reducing effect of comb-like extensions, which are fixed to the leading edge of a low-speed airfoil. The measurements took place in an aeroacoustic wind tunnel using the microphone array technique, while the aerodynamic performance of the modified airfoils was captured simultaneously. It was found that the comb structures lead to a noise reduction at low frequencies, while the noise at high frequencies slightly increases. The most likely reasons for this frequency shift are that the teeth of the combs break up large incoming turbulent eddies into smaller ones or that they shift turbulent eddies away from the airfoil surface, thereby reducing pressure fluctuations acting on the airfoil. The aerodynamic performance does not change significantly.

22nd AIAA/CEAS Aeroacoustics Conference, 2016

The interaction of a turbulent flow with the leading edge of a blade is a main noise source mecha... more The interaction of a turbulent flow with the leading edge of a blade is a main noise source mechanism especially for wind turbines, which are often exposed to intense atmospheric turbulence with a wide range of length scales. The present paper describes an experimental study performed to explore the noise reducing effect of hook-like extensions, which are fixed to the leading edge of a low speed airfoil. The measurements took place in an aeroacoustic wind tunnel using microphone array technique, while simultaneously the aerodynamic performance of the modified airfoils was captured. It was found that the hook structures lead to a noise reduction at low frequencies, while the noise at high frequencies slightly increases. The aerodynamic performance does not change significantly.

Journal of Wind Engineering and Industrial Aerodynamics

Noise disturbance is one of the major factors considered in the development of wind farms near ur... more Noise disturbance is one of the major factors considered in the development of wind farms near urban areas, and therefore an accurate estimate of the noise levels generated by wind turbines is required before production and installation. Horizontal-axis wind turbines are the most popular type of turbines and the aeroacoustic noise generated by their rotating blades is known to be the most significant noise source. The region of the turbine blade that produces the strongest acoustic sources has been identified in published acoustic camera measurements. In the present work, a Large Eddy Simulation (LES) of this region is carried out using an annular computational domain, which leads to a significant reduction of computational expense compared to full blade simulations. The Ffowcs-Williams and Hawkings (FW–H) acoustic analogy is then used to predict the far field sound. Numerical results for a simulation of the CART-2 wind turbine show good agreement with the available experimental data.

NOISE-CON ... proceedings, Nov 29, 2023

2023 29th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)

IEEE Transactions on Components, Packaging and Manufacturing Technology

INTER-NOISE and NOISE-CON Congress and Conference Proceedings

2022 28th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC)

48th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2019 MADRID, Madrid, 2019

25th AIAA/CEAS Aeroacoustics Conference, 2019

Airframe is considered to be one of the primary noise sources during aircraft take off and landin... more Airframe is considered to be one of the primary noise sources during aircraft take off and landing maneuvers, causing disturbance to the people living vicinity to airports. With the increasing demand for air transportation, there is need to innovate new technologies to reduce airframe noise. High lift device noise, in particular the wing-flap noise, gives a considerable contribution to the total airframe noise levels. This paper investigates the noise from a simplified wing-flap configuration and possibility of reducing the noise with the use of a Dielectric Barrier Discharge (DBD) plasma actuator. A compressible SST k- based Improved Delayed Detached Eddy Simulation (IDDES) has been used to simulate the unsteady flow field. The Ffowcs-Williams and Hawkings (FW-H) acoustic analogy has been used to predict the far field noise. The effects of plasma has been modeled as volumetric body force source, based on the Suzen and Huang model. Results indicate a noise reduction of about 2.5 dB ...

INTER-NOISE and NOISE-CON Congress and Conference Proceedings

Acoustics, Apr 1, 2020

22nd AIAA/CEAS Aeroacoustics Conference, 2016

The interaction of a turbulent flow with the leading edge of a blade is a main noise source mecha... more The interaction of a turbulent flow with the leading edge of a blade is a main noise source mechanism especially for wind turbines, which are often exposed to intense atmospheric turbulence with a wide range of length scales. The present paper describes an experimental study performed to explore the noise reducing effect of hook-like extensions, which are fixed to the leading edge of a low speed airfoil. The measurements took place in an aeroacoustic wind tunnel using microphone array technique, while simultaneously the aerodynamic performance of the modified airfoils was captured. It was found that the hook structures lead to a noise reduction at low frequencies, while the noise at high frequencies slightly increases. The aerodynamic performance does not change significantly.

Journal of Wind Engineering and Industrial Aerodynamics

Noise disturbance is one of the major factors considered in the development of wind farms near ur... more Noise disturbance is one of the major factors considered in the development of wind farms near urban areas, and therefore an accurate estimate of the noise levels generated by wind turbines is required before production and installation. Horizontal-axis wind turbines are the most popular type of turbines and the aeroacoustic noise generated by their rotating blades is known to be the most significant noise source. The region of the turbine blade that produces the strongest acoustic sources has been identified in published acoustic camera measurements. In the present work, a Large Eddy Simulation (LES) of this region is carried out using an annular computational domain, which leads to a significant reduction of computational expense compared to full blade simulations. The Ffowcs-Williams and Hawkings (FW–H) acoustic analogy is then used to predict the far field sound. Numerical results for a simulation of the CART-2 wind turbine show good agreement with the available experimental data.