Browsing by Author "Delgado, A."

Now showing 1 - 10 of 10

Metadata only
A Complete procedure for predicting and improving the performance of HAWT's
(IOP Publishing, 2014) Al-Abadi, A.; Ertunç, Özgür; Sittig, F.; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
A complete procedure for predicting and improving the performance of the horizontal axis wind turbine (HAWT) has been developed. The first process is predicting the power extracted by the turbine and the derived rotor torque, which should be identical to that of the drive unit. The BEM method and a developed post-stall treatment for resolving stall-regulated HAWT is incorporated in the prediction. For that, a modified stall-regulated prediction model, which can predict the HAWT performance over the operating range of oncoming wind velocity, is derived from existing models. The model involves radius and chord, which has made it more general in applications for predicting the performance of different scales and rotor shapes of HAWTs. The second process is modifying the rotor shape by an optimization process, which can be applied to any existing HAWT, to improve its performance. A gradient- based optimization is used for adjusting the chord and twist angle distribution of the rotor blade to increase the extraction of the power while keeping the drive torque constant, thus the same drive unit can be kept. The final process is testing the modified turbine to predict its enhanced performance. The procedure is applied to NREL phase-VI 10kW as a baseline turbine. The study has proven the applicability of the developed model in predicting the performance of the baseline as well as the optimized turbine. In addition, the optimization method has shown that the power coefficient can be increased while keeping same design rotational speed.
Metadata only
A design and optimization method for matching the torque of the wind turbines
(AIP Publishing, 2015) Al-Abadi, A.; Ertunç, Özgür; Weber, H.; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
An aerodynamic shape optimization method for a horizontal axis wind turbine is developed and verified through experimentation with a laboratory-scale wind turbine. Our method is based on matching the rotor's and the coupled generator's torque. Prior to shape optimization, an initial rotor design is established with a hybrid use of Schmitz and blade element momentum theories. The experimental verification of the developed method is conducted with a small-scale wind turbine; thus, the operating Reynolds number is one order of magnitude lower than large-scale wind turbines. Therefore, a high-lift low-Re airfoil, namely, SG6043, is selected for the blade along the whole span. The shape is optimized by determining the optimum chord and cumulative pitch angle distributions by manipulating the tapering and twisting of the blade. The objective of the optimization is to maximize the turbine's power coefficient Cp , while maintaining the torque equal to that of the generator. The generator's characteristics are found through experimentations which are conducted apart from the wind tunnel experiments. During the optimization process, the local aerodynamic forces on the blade are calculated by interfacing the optimization program with XFOIL; thus, the torque and power can be calculated for the rotor at each iteration step. The optimized turbine performance is evaluated under a design and off-design operating condition. The performance verification experiments are carried out in the wind tunnel with a specially designed setup. A comparison of the measured and computed performance shows good agreement.
Metadata only
From passive to active pitch regulation of wind turbines: Optimization method with numerical validation
(ASME, 2015) Al-Abadi, A.; Kim, Y.; Park, J.-Y.; Kang, H.; Ertunç, Özgür; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
An optimization method that changes the control strategy of the Horizontal Axis Wind Turbine (HAWT) from passive- to active-pitch has been developed. The method aims to keep the rated power constant by adjusting the blade pitch angle while matching the rotor and the drive torques. The method is applied to an optimized wind turbine model. Further, numerical simulations were performed to validate the developed method and for further investigations of the flow behavior over the blades.
Metadata only
High-speed visualization of acoustically excited cavitation bubbles in a cluster near a rigid boundary
(Springer Berlin Heidelberg, 2017) Vaidya, H. A.; Ertunç, Özgür; Lichtenegger, T.; Hachmann, J.; Delgado, A.; Skupin, A.; Mechanical Engineering; ERTUNÇ, Özgür
In the present work, high-speed visualizations at one million frames/s have been used to study the oscillation characteristics of acoustic cavitation bubbles. The bubbles are generated by acoustic cavitation using an ultrasound transducer with an excitation frequency of 75 kHz near a rigid surface and the medium used is deionized water. The cavitation bubbles tend to collect in clusters near solid boundaries, where they are visualized using a high-speed camera. The collective oscillations give rise to many interesting phenomena like bubble collapse, coalescence, fragmentation and bubble translation. The image sequences provided here contribute to the better understanding of the entire lifecycle of acoustic cavitation bubbles.
Open Access
Interaction between free-stream turbulence and tip-vortices of wind turbine blades with and without winglets
(IOP Publishing, 2018) Al-Abadi, A.; Kim, Y.; Ertunç, Özgür; Epple, P.; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
Experimental investigations of the free-stream turbulence impact on the tip-vortices generated in wind turbine blades have been performed. The investigation is done by exposing an efficient laboratory scale wind turbine to different turbulence levels generated by two static grids installed in the cross section of a wind tunnel. Different winglet configurations to figure out the optimum design that can prevent the tip induced flow are studied. The power gained when adding different winglets is measured when exposing the turbine to turbulence. It is found that the strength of the vortices is reduced depending on the turbulence levels. Furthermore, higher power extraction associated with more expansion of wake and wake-border is shown. This is an indication for increasing of the mixing between the free-stream and the wake. Tip-vortex analysis of high turbulence levels has shown additional interaction of large-eddy scales contained in the free-stream turbulence. The turbulence helps to suppress the tip vortices, and thus, reduces the tip losses. Further investigations of the near and far wake-surrounding intersection are performed to understand the energy exchange and the free stream entrainment that help in wake recovery.
Metadata only
Numerical and experimental analysis of impinging synthetic jets for cooling a point-like heat source
(ASME, 2018-05-01) Glowienko, G.; Derlien, H.; Ertunç, Özgür; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
High power light emitting diodes (LEDs) being used for low and high beam in automotive lighting need active cooling of their heat sinks by radial or axial fans. But the moving elements of the fan cause abrasion, noise, and high energy consumption. Synthetic jets can replace conventional fans with their disadvantages and allow the directed cooling of LEDs. Therefore, in this paper, flow and heat transfer characteristics of impinging synthetic jets are investigated numerically and experimentally as an alternative to cooling LEDs with fans. It is shown that the impact plate brings forward the laminar-turbulent transition of the jets temporally and spatially. The impact plate itself should not be positioned in the region of the free jet's transition height. Increasing the frequency of the synthetic jet has a greater influence on the heat transfer compared to an increase in amplitude. The maximum cooling performance is achieved for all jet configurations with moderate distances between the orifice and the impact plate. In this case, the jet reaches its highest mass flow and impulse and its lowest temperature.
Metadata only
Numerical and experimental analysis of the flow and transition of free synthetic jets
(IOP Publishing, 2019-04) Glowienko, R.; Derlien, H.; Ertunç, Özgür; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
In this paper, flow characteristics and the transition of synthetic jets are investigated numerically and experimentally. The investigated synthetic jets have a dimensionsless stroke length L-0/d of 146 and 167, an U-0 of 7.3 and 8.35 m s(-1) and a jet Reynolds number Re-U0 of 471 and 539. Novelty of this paper is the extensive analysis and explanation of why synthetic jets with L-0/d > 70 result to transition and turbulent flow: it is shown that the jets exhibit swirl which originates from the cavity. The rotation results in more rapid divergence and deceleration of the free jets. Both processes initially cause disruptions of the primary vortex and the secondary vortices, also vortex breakdown, and ultimately result in jet turbulence. Extension of the laminar region spatially and temporally is possible by increasing the height of the cavity.
Metadata only
The penetration of acoustic cavitation bubbles into micrometer-scale cavities
(Elsevier, 2016) Vaidya, H. A.; Ertunç, Özgür; Lichtenegger, T.; Delgado, A.; Skupin, A.; Mechanical Engineering; ERTUNÇ, Özgür
The penetration of acoustically induced cavitation bubbles in micrometer-scale cavities is investigated experimentally by means of high-speed photography and acoustic measurements. Micrometer-scale cavities of different dimensions (width = 40 μm, 80 μm, 10 mm and depth = 50 μm) are designed to replicate the cross section of microvias in a PCB. The aim here is to present a method for enhancing mass transfer due to the penetration of bubbles in such narrow geometries under the action of ultrasound. The micrometer-scale cavities are placed in a test-cell filled with water and subjected to an ultrasound excitation at 75 kHz. A cavitation bubble cluster is generated at the mouth of the cavity which acts as a continuous source of bubbles that penetrate into the cavity. The radial oscillation characteristics and translation of these bubbles are investigated in detail here. It is observed that the bubbles arrange themselves into streamer-like structures inside the cavity. Parameters such as bubble population and size distribution and their correlation with the phase of the incident ultrasound radiation are investigated in detail here. This provides a valuable insight into the dynamics of bubbles in narrow confined spaces. Mass transfer investigations show that fresh liquid can be continuously introduced in the cavities under the action of ultrasound. Our findings may have important consequences in optimizing the filling processes for microvias with high aspect ratios.
Metadata only
A torque matched aerodynamic performance analysis method for the horizontal axis wind turbines
(Wiley, 2013-11) Al-Abadi, A.; Ertunç, Özgür; Weber, H.; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
An analysis method is developed to test the operational performance of a horizontal axis wind turbines. The rotor is constrained to the torque–speed characteristic of the coupled generator. Therefore, the operational conditions are realized by matching the torque generated by the turbine over a selected range of incoming wind velocity to that needed to rotate the generator. The backbone of the analysis method is a combination of Schmitz' and blade element momentum (BEM) theories. The torque matching is achieved by gradient-based optimization method, which finds correct wind speed at a given rotational speed of the rotor. The combination of Schmitz and BEM serves to exclude the BEM iterations for the calculation of interference factors. Instead, the relative angle is found iteratively along the span. The profile and tip losses, which are empirical, are included in the analysis. Hence, the torque at a given wind speed and rotational speed can be calculated by integrating semi-analytical equations along the blade span. The torque calculation method is computationally cheap and therefore allows many iterations needed during torque matching. The developed analysis method is verified experimentally by testing the output power and rotational speed of an existing wind turbine model in the wind tunnel. The generator's torque rotational speed characteristic is found by a separate experimental set-up. Comparison of experiments with the results of the analysis method shows a good agreement.
Metadata only
Turbulence impact on wind turbines: experimental investigations on a wind turbine model
(IOP Publishing, 2016) Al-Abadi, A.; Kim, Y. J.; Ertunç, Özgür; Delgado, A.; Mechanical Engineering; ERTUNÇ, Özgür
Experimental investigations have been conducted by exposing an efficient wind turbine model to different turbulence levels in a wind tunnel. Nearly isotropic turbulence is generated by using two static squared grids: fine and coarse one. In addition, the distance between the wind-turbine and the grid is adjusted. Hence, as the turbulence decays in the flow direction, the wind-turbine is exposed to turbulence with various energy and length scale content. The developments of turbulence scales in the flow direction at various Reynolds numbers and the grid mesh size are measured. Those measurements are conducted with hot-wire anemometry in the absence of the wind-turbine. Detailed measurements and analysis of the upstream and downstream velocities, turbulence intensity and spectrum distributions are done. Performance measurements are conducted with and without turbulence grids and the results are compared. Performance measurements are conducted with an experimental setup that allow measuring of torque, rotational speed from the electrical parameters. The study shows the higher the turbulence level, the higher the power coefficient. This is due to many reasons. First, is the interaction of turbulence scales with the blade surface boundary layer, which in turn delay the stall. Thus, suppressing the boundary layer and preventing it from separation and hence enhancing the aerodynamics characteristics of the blade. In addition, higher turbulence helps in damping the tip vortices. Thus, reduces the tip losses. Adding winglets to the blade tip will reduce the tip vortex. Further investigations of the near and far wake-surrounding intersection are performed to understand the energy exchange and the free stream entrainment that help in retrieving the velocity.