Experimental investigation of leading-edge roughness effects on stationary crossflow instability of a swept wing

AbstractWind tunnel experiments were conducted to evaluate surface pressure distribution over a semi span swept wing with a sweep angle of 33°. The wing section has a laminar flow airfoil similar to that of the NACA 6-series. The tests were conducted at speeds ranging from 50 to 70 m/s with and without surface roughness. Surface static pressure was measured on the wing upper surface at three different chordwise rows located at the inboard, middle, and outboard stations. The differences between pressure distributions on the three sections of the wing were studied and the experimental results showed that roughness elements do not influence the pressure distribution significantly, except at the inboard station. On the other hand, spectral analysis of the pressure–time signals acquired from the pressure orifices over the wing upper surface showed that roughness had significantly affected the zero frequency amplitude. In this study, the zero frequency amplitude and its variations with roughness elements was investigated at three different chordwise positions; inboard, middle, and outboard stations. Results showed that the 3-D roughness elements amplified zero frequency amplitude over the wing surface. Zero frequency distribution at the inboard station, closer to the wing root, in comparison with the middle station, was reduced after an initial amplification along the chord. Moreover, the effect of roughness on the zero frequency instability at the first section was negligible due to the narrow instability amplification region. On the other hand, at the outboard station, closer to the wing tip, the instabilities were amplified over a larger region, with respect to the middle station

An experimental study of the effects of swept angle on the boundary layer of the 2D wing

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.dc201

Experimental investigation of shock-buffet criteria on a pitching airfoil

An experimental investigation of the shock-buffet phenomenon subject to unsteady pitching supercritical airfoil around its quarter chord has been conducted in a transonic wind tunnel. The model was equipped with pressure taps connected to the fast response pressure-transducers. Measurements were conducted at different free-stream Mach number from 0.61 to 0.76. The principle goal of this investigation was to experimentally discuss the shock-buffet criterion over a SC(2)-0410 supercritical pitching related to the hysteresis loops of total drag and trailing edge pressure, the behaviour of the shock wave foot location, the pressure distribution over the upper surface, and by implementing the wavelet analysis of the normal force. To ensure capturing the buffet phenomenon by utilizing these criteria, a pressure port has been drilled exactly at the trailing edge of the airfoil where its output was used to detect the buffet phenomenon for different conditions. Visual representation of the flow using the shadow graph flow visualization technique for different test cases is further used to illustrate the unsteady shock wave motion. A comparative analysis of experimental measurements shows that the conducted criteria confirm each other when the buffet phenomenon occurs at the position of the oscillating cycle

Optimization of Power and Levelized Cost for Shrouded Small Wind Turbine

Nowadays, by increasing energy demand and considering the importance of environmental issues in recent decades, the use of renewable energies is expanding. Among renewable energies, wind power and its technology are growing and evolving more rapidly. Resource assessment in Iran has revealed the significant potential of wind energy around the country. To further develop wind energy in the country and create large-scale wind power plants, the consideration of distributed power generation using small wind turbines for applications in agricultural and residential use is needed. Conventional small wind turbines and small wind lens turbines have been developed in recent years. In this research project, a small wind lens turbine is designed. The advantages of this turbine are an increased production capacity and reduced cut-in speed and noise pollution. In this study, a lens (or shroud) is added to a small turbine, and the maximized annual energy production (AEP) and minimization of the levelized cost of energy (LCOE) are modeled. We applied the NSGA-II algorithm for optimization to find the best answer. The input parameters in the objective function of the AEP are cut-in, cut-out, rated speeds, scale factor, and shape factor. Additionally, the input parameters in the objective function of the LCOE are the power production, initial capital cost, annual operating expenses, and balance of energy. The results indicate that installing a wind lens turbine in Kish Island led to an LCOE decrease of 56% on average, and we can see an 83% increase in the AEP. In the Firoozkooh area, an average reduction of 59% in the LCOE and 74% increase in the AEP for a wind lens turbine is observed

Effect of second wing on the surface pressure of an MAV model

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.In this study surface pressure distribution over a Zimmerman type wing generally used for the MAV models in the presence of a second wing located on the top of the main wing was experimentally investigated. The model was tested in a low speed, low turbulence tunnel. Surface pressure data for various angles of attack and Reynolds numbers in the presence of the second wing is obtained. In addition, all data were repeated for the different locations, vertical and horizontal, positions of the second wing. The data are compared with those of the main wing alone. By comparing the surface pressure data for various cases one can clearly identify the best location, vertical and longitudinal, of the second wing. From the pressure data, it is seen that addition of the second wing affects the flow field over the main wing considerably. It increases the surface pressure distribution in front portion of the main wing, unfavourable effect, while it has a favourable effect in the rear portion of the wing.dc201

An experimental study on boundary layer transition detection over a pitching supercritical airfoil using hot-film sensors

In the present work, experimental tests are conducted to study boundary layer transition over a supercritical airfoil undergoing pitch oscillations using hot-film sensors. Tests have been undertaken at an incompressible flow. Three reduced frequencies of oscillations and two mean angles of attack are studied and the influences of those parameters on transition location are discussed. Different algorithms are examined on the hot-film signals to detect the transition point. Results show the formation of a laminar separation bubble near the leading edge and at relatively higher angles of attack which leads to the transition of the boundary layer. However, at lower angles of attack, the amplification of the peaks in voltage signal indicate the emergence of the vortical structures within the boundary layer, introducing a different transition mechanism. Moreover, an increase in reduced frequency leads to a delay in transition onset, postponing it to a higher angle of attack, which widens the hysteresis between the upstroke and downstroke motions. Rising the reduced frequency yields in weakening or omission of vortical disturbances ensuing the removal of spikes in the signals. Of the other important results observed, is faster movement of the relaminarization point in the higher mean angle of attack. Finally, a time–frequency analysis of the hot-film signals is performed to investigate evolution of spectral features of the transition due to the pitching motion. An asymmetry is clearly observed in frequency pattern of the signals far from the bubble zone towards the trailing edge; this may reflect the difference between the transition and relaminarization physics. Also, various ranges of frequency were obtained for different transition mechanisms

TRACTOR: Traffic‐aware and power‐efficient virtual machine placement in edge‐cloud data centers using artificial bee colony optimization

Technology providers heavily exploit the usage of edge‐cloud data centers (ECDCs) to meet user demand while the ECDCs are large energy consumers. Concerning the decrease of the energy expenditure of ECDCs, task placement is one of the most prominent solutions for effective allocation and consolidation of such tasks onto physical machine (PM). Such allocation must also consider additional optimizations beyond power and must include other objectives, including network‐traffic effectiveness. In this study, we present a multi‐objective virtual machine (VM) placement scheme (considering VMs as fog tasks) for ECDCs called TRACTOR, which utilizes an artificial bee colony optimization algorithm for power and network‐aware assignment of VMs onto PMs. The proposed scheme aims to minimize the network traffic of the interacting VMs and the power dissipation of the data center's switches and PMs. To evaluate the proposed VM placement solution, the Virtual Layer 2 (VL2) and three‐tier network topologies are modeled and integrated into the CloudSim toolkit to justify the effectiveness of the proposed solution in mitigating the network traffic and power consumption of the ECDC. Results indicate that our proposed method is able to reduce power energy consumption by 3.5% while decreasing network traffic and power by 15% and 30%, respectively, without affecting other QoS parameters

Performance optimization of a dual-rotor ducted wind turbine by using response surface method

The presented study evaluates and optimizes the performance of dual-rotor wind turbines installed inside a developed duct. The effect of different operating conditions on the extracted power was compared between dual-rotor wind turbines (DRWT) and single rotor wind turbines (SRWT). These operating conditions include the type of dual-rotor wind turbines installed in the throat section of the duct, the distance between the two rotors of a turbine, and the flow velocity through the duct throat that were evaluated by the multivariate statistical method response surface methodology. The central composite design of the response surface method was utilized to fit the designed model based on the least-squares method. Also, the multiple regression method was applied for the empirical data to match variable operating conditions with the developed model by analysis of variance (ANOVA). Afterward, some experiments were carried on to validate this method. The results showed a maximum power ratio of about 55% at the optimized conditions for dual rotor wind turbines. Determined P-values for designed parameters of models were less than 0.05, which makes its effect on the model significant. Furthermore, the power ratio obtained from empirical data was compatible with the considered model

An experimental study of sweep angle effects on the transition point on a 2D wing by using hot-film sensor

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Location of transition point over a 2-D swept wing was investigated. A series of wind tunnel tests were performed to predict the transition location over three models of swept wing having same aspect ratio, and at various angles of attack and sweep angles by hot-film anemometer. Two flat plates were used at the ends of the models to prevent the flow to roll up and to reduce the boundary layer effect of the test section on the models, but the flow field on the model was still 3D because of the swept angle effects that led to formation of cross flow over the wing surface. Due to the complexity of the calibration of the hot film sensors, as well as various sources of errors in the calibration process, the hot film sensors were not calibrated and their signal is qualitatively investigated. Data obtained from the hot film sensor signal indicates that as the swept angle increases, the position of transition moves toward the leading edge of the wing due to strengthening of the cross flow about the leading edge, and transition occurs at a smaller angle of attack. Increasing the angle of attack also moved the position of transition point closer to the leading edge of the wing. The transition line is approximately parallel to the x/c local line which may indicate that the strength of cross flow is nearly constant on each line parallel to the c/4 local line.dc201

Correction to: Improved Butterfly Optimization Algorithm for Data Placement and Scheduling in Edge Computing Environments (Journal of Grid Computing, (2021), 19, 2, (14), 10.1007/s10723-021-09556-0)

A Correction to this paper has been published: https://doi.org/10.1007/s10723-021-09562-2. © 2021, Springer Nature B.V