Passive Control Method Research Articles

Research on the aerodynamic performance of the wind turbine blades with leading-edge protuberances

The aerodynamic performance loss of wind turbine blades caused by severe flow separation is one of the main reasons for hindering the utilization of offshore wind energy. The leading-edge protuberances (LEPs) have been shown to be an effective passive control method with suppressed flow separation. This paper proposes a method for predicting the effect of the LEPs on the aerodynamic performance of the wind turbine airfoil and develops an optimized design method for the parameters of the LEPs. The GH-Bladed platform is used to verify the influence of the LEPs method on the load performance of the blades. The study found that the developed method can realize the optimization design of the aerodynamic performance for the wind turbine airfoil with LEPs, and obtain the structural parameters of the LEPs to improve the value CL/CD by 2%–11% in the post-stall region. Moreover, the average load and the standard deviation of the load for the blades with LEPs are reduced by 7% and 17% respectively near the rated wind speed of 8.7 m/s. This study realized the feasibility of the optimal design of the wind turbine airfoil with LEPs and verified the effectiveness of the LEPs technology applied to wind turbine blades.

Self-adaptive turbulence eddy simulation of flow control for drag reduction around a square cylinder with an upstream rod

The use of an upstream circular rod to control the flow around a downstream square cylinder is found to efficiently reduce the drag of the square cylinder. The complex flow characteristics and mechanism of the rod-square system in tandem arrangement as a passive flow control method for various centre-to- centre gap ratios (L/D) are investigated by numerical simulation. Turbulence modelling of the rod-square cylinder system is challenging. To select a suitable turbulence modelling, the recently developed Self-Adaptive Turbulence Eddy Simulations (SATES), as well as IDDES (Improved Delayed Detached Eddy Simulation) and SBES (Stress Blended Eddy Simulation) are first assessed for single circular and single square cylinder flow test cases. The SATES method performs best among the three models for bluff body flow simulation and is thus used in the drag flow control study. For the rod-square flow control system, the Reynolds number is 34000 based on freestream velocity U0 and the edge length of the square cylinder D. The diameter of the control rod is kept constant at d/D = 0.18. The flow characteristics and mechanism are explored in detail, varying the rod and square cylinder distance of L/D = 1.5, 2.0, 2.5and 3.0. According to the absence or presence of vortex shedding from the upstream rod cylinder, two flow patterns (pattern I and pattern II) are observed. Large drag reduction is observed for all the simulation cases the maximum drag reduction is approximately 63% with L/D = 2.0, and the minimum drag reduction approximately 53% with L/D = 3.0. The secondary lock-frequency, which presents as pattern II, is caused by the excitation of upstream vortices. It is found that the side recirculation is associated with the wake recirculation length of the square cylinder, which is similar to the elongated cylinder in the flow pattern I. The flow mechanism of suppression of the vortices from the rod can be attributed to the effective diffusion of vorticity in the separating shear layer caused by the presence of the front wall of the square cylinder.

Flow and acoustic characteristics of convergent-divergent nozzle with and without wedges

The advancements in flight have increased over the years to achieve and provide comfortable flights to passengers. In addition to shorter travel time, passengers expect good comfort and an eco-friendly environment with no noise around them. Most of the present turbofan engines are producing much noise due to the supersonic jets created at the nozzle. By increasing the mixing rate at the exit, it is possible to reduce the noise and increase the performance. The enhanced flow mixing can be achieved by using many methods such as active and passive control methods including co-flow jets and tabs. Here in this research, the selected method to provide the controlled jet was using wedges. The significance of using this method is its mixing efficiency by following the principle of entrainment of atmospheric air into the exit jet. The wedges used here act as a vortex generator. These produced vortices weaken the shocks and the shear layer thus the potential core length is reduced. The CFD analysis and experimental analysis were also done and the results were compared. The experimental analysis was carried out without and with a wedge nozzle. In experimental analysis 2 bar and 4.74, bar gauge pressure was used and for both cases and the Mach Number was 1.8. The high-speed jet facility schlieren flow visualization and acoustic analysis were carried out. In CFD analysis flow characteristics of 2 bar gauge pressure such as contours and graphs were obtained for both with and without wedge nozzle. From the results, it is clear that the second shock-cell length was reduced with the use of wedges.

Field test study for evaluation of vibration control capacity of cracked mass concrete layer

Passive control is typically implemented to regulate ground vibration in advanced ultra-precision and large-scale synchrotron radiation facilities. This paper presents the field test to evaluate the influence of cracks on the vibration control capacity of a mass concrete layer used as a passive control method of an advanced synchrotron radiation facility. Simplified finite element model (FEM) analysis is utilized to simulate the cracks and analyze the key factor that influences the vibration control capacity of the mass concrete layer. In the field test, cracks are artificially formed by creating cuts in two orthometric directions on the surface of a 3-m-thick concrete layer. Measurement points and a vibrator capable of generating simple harmonic excitation (1–100 Hz) are positioned along a straight line. Velocity signals vertical to the ground are obtained to study the vibration attenuation in the vertical direction. Test results indicate that the velocity signals on the concrete layer are sensitive to the cracks; the vibration control ability of the concrete layer is slightly affected by the depth, length and location of the cracks in the frequency band of 1–100 Hz. The proposed simplified FEMs can reflect the cracked concrete layer’s vibration control ability from 1 to 100 Hz. Numerical study results indicate that the thickness of the concrete layer rather than the density or elastic modulus is the key factor in vibration control ability.

Investigation for the effect of the column step on the flow-induced motion of a TLP

Significant flow-induced motion (FIM) can severely threaten the security of large marine floaters, which has brought paid more and more attention in academia and engineering. It is necessary to study the effective control methods to mitigate the FIM, commonly divided into active control and passive control methods. In this study, seven different column step variations including three parameters (cross section shapes, circumferential coverage and radial thickness), are presented as passive control methods to break the coherence of the vortex structures along the columns, and FIM responses are expected to be mitigated. To investigate the suppression effect of these various column steps on the FIM behaviors of a Tension Leg Platform (TLP), experimental tests were conducted in a towing tank. Three typical incident angles, i.e., 0∘, 45∘, and 90∘-incidences were tested. The results showed that the mitigation effect of each column step on the transverse motion response varied with the type of the column step and the incident angle. The column steps produced the most significant reduction in the transverse motions at 0∘-incidence, while the reduction was the most negative at 90∘. However, the drag coefficient did not show a big difference at 0∘ and 90∘, rather than the transverse motion. In addition, only the FSAS (with the column steps of 90∘ circumferential coverage, 1/4 column diameter for radial thickness, and arc shape) exhibited positive mitigation effect at all tested current incidences for the transverse FIM response.

Study on enhanced heat transfer of a phase change material slurry in transverse corrugated tubes

Enhancing the heat transfer of ice slurry is a key to improving its application. The outward transverse corrugated tube (OTCT) presents a better heat transfer enhancement as an effective passive flow control method. In this paper, the thermo-fluidic performance and enhanced heat transfer mechanism of ice slurry in OTCT are numerically studied using Euler-Euler multiphase model. The results indicated that turbulent vortex of ice slurry in OTCT is enhanced with the rise in the ratio of corrugation height to diameter (H/D), and declined with rising the of ratio corrugation pitch to diameter (P/D), and ratio of corrugation pitch to width (W/D). The ice concentration presents a periodic fluctuation along the flow direction. The values of H/D, W/D, and P/D have a significant influence on the mass transfer for ice slurry. And the ice particle concentration displays more even distribution as increasing H/D, and decreasing W/D and the P/D. The average flow resistance (fave) and Nusselt number (Nuave) increase with the increasing H/D and decreasing P/D, and decrease with increasing W/D. Nuave presents a linear increase with Re. For the inlet ice volume fraction of αin = 10%, Nuave enlarges significantly by increasing the Re from 4950 to 9540 for different H/D, P/D, and W/D values. The performance evaluation criterion (PEC) reaches a maximum value for different H/D and P/D at Re = 9540 when W/D = 0.4, αin = 10%. For bigger inlet ice particle concentration, the increment of Nuave of ice slurry in OTCT is more significant at higher Re compared with the smooth tube. Meanwhile, under higher ice concentration, the overall heat transfer performance is more prominent at large Re. Finally, the empirical correlations of the fave and Nuave are established to predict the thermal–hydraulic performance of ice slurry flowing through OTCT.

Experimental investigation on cylinder noise and its reductions by identifying aerodynamic sound sources in flow fields

Through anechoic wind tunnel tests, this study comprehensively investigates the noise and drag reductions on a circular cylinder with dimples. Dimples built on a surface pattern fabric cover the cylinder surface as one of the passive flow control methods. The force, noise, and flow field measurements are performed at diameter-based Reynolds numbers ranging from 3×104 to 1.3×105, covering the sub-critical, critical, and supercritical regimes. The force and noise measurement results show that dimple fabric simultaneously reduces noise and drag in the critical regime. The changes in flow structures were characterized by the Time-resolved Particle Image Velocimetry (TR-PIV) measurements. Based on the vortex sound theory, the flow analysis shows that the dominant sound sources are found to be concentrated near the cylinder surface, which is caused by the unsteady vortex motions near the separation locations during the process of vortex shedding. The cross-correlation between the synchronized TR-PIV and microphone measurements further supports the conclusions. Moreover, the cylinder noise reductions controlled by the dimples are directly associated with the reduced sound sources in the critical and supercritical regimes, corresponding to the reduced strength of the vortex shedding.

Control strategy effect on storage performance for packed-bed thermal energy storage

Energy storage will play an essential role by complementing renewable energy sources, which are central to the decarbonization of the power sector. Sensible thermal energy storage (TES) system through heating materials with high-temperature heat transfer fluid (HTF) is the simplest and most inexpensive TES technology. However, the inherent disadvantage of thermocline degradation makes the packed-bed TES system has several negative consequences. In the present study, a passive thermocline control (TCC) method with a high ratio of height-diameter and an active TCC method by setting an ending charging temperature were proposed. The results showed that the heat transfer between air and solid thermal storage materials was enhanced because of the fast airflow and the long airflow passage of the TES system with the passive TCC method. The utilization factors were about 75%, and thermal energy efficiencies were about 78%–80% under different interval times between charging and discharging. Combined with the active TCC method, the stable discharging duration was 6%–19% longer than just using the passive TCC method.

Passive flow control via tip grooving and stall fencing mechanisms of a marine energy harvesting turbine

Remarkable advancement in wave energy conversion technology has taken place in recent years. Due to its simplicity, the Wells turbine has been one of the most widely used power take-off mechanisms in an oscillating water column type wave-energy conversion device. However, the turbine suffers from several challenges due to its narrow operating range, which hinders the commercial feasibility of the system. Several aerodynamic applications have successfully used passive control methods to modify the flow conditions. This work applied a combination of stall fences and casing grooves for passive flow control of a Wells turbine. The computational fluid dynamics (CFD) technique is used to analyze the modified turbine numerically. The casing groove modified the tip-leakage vortices, interacted with local vortices created by the stall fences, and helped reattach the flow at higher flow coefficients. As a result, the modified turbine increases the operating range up to 33.3%. In addition, the peak-to-average (PTA) power ratio decreased by up to 27.7%.

A theoretical study on the interplay of thermoacoustic modes with Helmholtz dampers in a longitudinal combustor

Thermoacoustic instabilities often present in gas turbine combustors, especially in land-based heavy-duty gas turbines. Normally, thermoacoustic modes can be classified into two sets: acoustic mode and intrinsic mode (ITA mode). Low order network models are usually used to study thermoacoustic instabilities and passive control methods such as liners and Helmholtz dampers are often used to suppress these instabilities. The addition of Helmholtz dampers could suppress the original thermoacoustic modes. Meanwhile, it could also introduce a new mode, the eigenfrequency of which is related to the parameters of the Helmholtz damper, including its resonant frequency and neck mean flow Mach number. The damping effects depend on the system parameters and could be different on the two categories of original thermoacoustic modes. Based on a rational design, both original modes can be controlled by one damper. The new mode introduced by the damper could interplay with original modes to form new exceptional points with certain parameters. In that case, the eigenfrequency and mode shape of original modes could be vastly influenced. The theoretical results will be verified by numerical simulations.

Impact of Slots on the Aerodynamic Performance of the Variable Inlet Guide Vane Cascade of a Centrifugal Compressor

This study reconstructed the flow field of a symmetrical variable inlet guide vane in a centrifugal compressor through the passive control method of vane slots. Based on the high-fidelity numerical simulation model verified by experiments, the influence of different slot forms on the flow field was investigated, and the passive control mechanism was revealed. The results demonstrated that the vane slot method can effectively suppress the suction surface separation and broaden the range of low-loss incidence angles. Overall, the 50_30 slotted vane achieves the best flow field control, with a 65.6% reduction in the total pressure loss coefficient and a 2.3° reduction in the deviation angle, respectively, at a 25° incidence angle. The linear characteristics of the pre-swirl grade variation curve with variable inlet guide vane incidence angles are also improved. Furthermore, changing the slot outlet angle has the most significant influence on the aerodynamic performance as it changes the throat width of the location, thereby affecting the flow rate and momentum of the jet. Finally, the impact of the velocity varies in the first self-similarity region on the slotted vane. The results indicate that, in contrast to the baseline vane, the suppression effect of the slot jet on the flow separation improves with the inlet velocity, whereas the deviation angle of the slotted vane declines with the inlet velocity. Meanwhile, the higher the incoming flow velocity, the better the slotted jet can inhibition of flow separation.

The effect of the vibrissa shaped cylinder on the aeolian tone mitigation

This paper studies vibrissa shaped cylinder as a passive control method for reducing the aerodynamic noise of the flow past a cylinder. One elliptical cylinder is also investigated for comparison. The far-field noise results show that compared with the cylinder case, the tonal peak almost disappears in the vibrissa shaped cylinder case and the sound pressure level (SPL) could be reduced by up to 30dB within the velocity range from 8m/s to 35m/s. The elliptical cylinder only shows a slight SPL reduction by about 4 dB with a shift in the tonal peak frequency from St=0.2 to St=0.39. Furthermore, some noticeable variations occur in the noise directivity pattern for the vibrissa shaped cylinder case. The shift in the tonal peak frequency, the reduction in noise and modifications in the noise directivity is related to the changing and breakdown of the vortex shedding caused by the interference with the elliptical and vibrissa shaped cylinder surfaces. The LES is conducted to the elliptical and vibrissa cylinder case for the fluid field information to further understand the mechanism of the noise reduction due to the vibrissa shaped cylinder and elliptical cylinder.

Unsteady Aerodynamic Design of a Flapping Wing Combined with a Bionic Wavy Leading Edge

Based on the bionic design of the humpback whale fin, a passive flow control method is proposed to obtain greater flapping lift by applying the wavy leading edge structure to the straight symmetrical flapping wing. The leading edge of the conventional flapping wing is replaced by the wavy shape represented by regular trigonometric function to form a special passive flow control configuration imitating the leading edge of the humpback whale fin. The dynamic aerodynamic performance and flow field characteristics of straight wing and wavy leading edge flapping wing with different parameters are compared and analyzed by CFD numerical simulation. The simulation results show that the wavy leading edge structure changes the flow field of the baseline flapping wing and reduces the pressure on the upper surface of the flapping wing during the process of downward flapping, thereby increasing the pressure difference between the upper and lower surfaces of the flapping wing and increasing the lift. The sensitivity analysis of the design parameters shows that in order to obtain the maximum lift coefficient while losing the least thrust, the smaller amplitude should be selected on the premise of selecting the smaller wavelength. Among the configurations of different design parameters calculated in this paper, the optimal wavy leading edge flapping wing configuration increases the time average lift coefficient by 32.86% and decreases the time average thrust coefficient by 14.28%. Compared with the straight wing, it has better low-speed flight and can withstand greater take-off weight.

Fast prediction and uncertainty analysis of film cooling with a semi-sphere vortex generator using artificial neural network

The advancement of aircraft engines relies heavily on film cooling technology. To enhance the film cooling efficiency in high-pressure turbines, many passive flow control methods have been explored. Downstream of the cooling hole, a semi-sphere vortex generator (SVG) decreases the lateral dispersion of the coolant and increases the efficiency of film cooling. To better understand the influence and uncertainty of SVG parameters such as the compound angle, size, and location, a supervised learning-based artificial neural network model is developed to identify the nonlinear mapping between the input parameters and the horizontal-averaged film cooling efficiency. Training data are generated by computational fluid dynamics. The model is quite accurate and stable after sufficient testing and validation. Through Monte Carlo simulations, the framework is used to analyze the thermal and flow characteristics of the film cooling efficiency. The radius of the SVG dominates the film cooling effectiveness at low blowing ratios, whereas at comparatively large blowing ratios, the angular placement of the SVG downstream of the cooling hole is the most important element. The angular position of the SVG has a much stronger impact than the distance at both low and high blowing ratios between the cooling hole and the SVG.

Dynamic kirigami structures for wake flow control behind a circular cylinder

A flow passing through a bluff body can produce Karman shedding vortex streets in its wake flow, resulting in strong unsteady loading and vibration. Existing passive control methods can disturb the wake flow, but are usually effective only under certain conditions and cannot adapt to changing environments due to their fixed topographies. Kirigami structures (the art of paper cutting) demonstrate programable out-of-plane buckling deformation under simple force actuations. By stretching and relaxing these kirigami sheets, an array of tilted surface elements can be easily activated and deactivated on the surface of a bluff body. For the first time, kirigami structures are used to achieve dynamic passive flow control. The control performance on the wake flow of a cylinder is validated in a wind tunnel using particle image velocimetry. Activated kirigami structures can push the shedding vortices further downstream from the cylinder by about four times of the uncontrolled one and reduce peak values of the turbulent intensity and Reynolds shear stress by 70% and 50%, respectively. The control performance is largely dependent on the height and shape of the kirigami structures.

Swing-up design of double inverted pendulum by using passive control method based on operator theory

Swing-up design of double inverted pendulum by using passive control method based on operator theory

A Review Paper on Comparative Analysis on RCC Structure with Energy Dissipation Device and Composite Structure

Abstract: In recent years considerable attention has been paid to research and development of structural vibration control devices with particular emphasis on mitigation of wind and seismic response of buildings. Many vibration-control measures like passive, active, semi-active and hybrid vibration control methods have been developed. Base isolation is a passive vibration control system. The isolator partially reflects and partially absorbs input seismic energy before it gets transmitted to the superstructure. Lead rubber bearing isolators are placed between the superstructure and foundation, which reduces the horizontal stiffness of the system. It thereby increases the time period of the structure and decreases the spectral acceleration of the structure. The superstructure acts like a rigid body, thus inter storey drift is reduced. This study is concerned with the effects of various vertical irregularities on the seismic response of a structure and controls this response using base isolation. The objective of the study is to carry out response spectrum analysis. The predominant lateral loads acting upon building structures are earthquake and wind induced forces. If wind load is much greaterthan earthquake load, the lateral force resisting system required to tackle wind loading may be enough to resist the smaller earthquake load. In this situation, a seismic base isolator will not bring any benefit to the building system. Furthermore, if time period of a building without isolator is greater, incorporation of isolator will not bring much difference to the building behavior with respect to seismic load. Additionally, for buildings with lowerstructural time periods, incorporation of an isolator will greatly alter the seismic behavior

Passive Flow Control of Ahmed Body using Control Rod

In the current study, numerical analysis of passive control flow with a control rod for Ahmed body is performed at different slant angles and velocities and placed rod locations on the slant surface. The aim of the study is to improve aerodynamic performance by preventing flow separation on the slant surface of Ahmed body using a control rod. This passive flow control method uses a control rod that has not been applied for simplified ground vehicles before. Therefore, it can be said that this study is a new example in point of a passive flow control application for Ahmed body. The solution of the study is performed by using the Computational Fluid Dynamics (CFD) method. The solutions are firstly performed for baseline geometry, and the results are compared with experimental data reported in the literature for validation. CFD solutions are carried out by means of the ANSYS and RNG k- turbulence model is used to simulate flow-field since it captures the effect of turbulent flow. The solutions used a control rod with a 20 mm diameter performed at a dimensionless location (X/L=0.057 and 0.153) for Ahmed body. The results are presented visually in the figures, and drag coefficient values are also given in Table format. It is concluded that the rod application is useful for some specified slant angles and velocities since flow separation delays and suppresses the slant surface. The maximum drag reduction is achieved at about 6.153% at a slant angle of 35° and 20 m/s velocity of air, and location of control rod of 0.057, while the minimum drag reduction is about 1.048% at slant angle of 25° and velocity of air at 40 m/s and location of control rod of 0.153.

A novel approach for suppressing leakage flow through turbine blade tip gaps

Tip clearance leakage flow of the turbine bade is an important factor limiting the augment of the high pressure turbine efficiency, which should be suppressed utilizing certain methods. However, the passive control method with the traditional structure is more and more difficult to satisfy the suppressing ability of the advanced turbine demand. In the present paper, a synergetic suppressing method by combining the approach of blade shape modification and spontaneous injection is adopted, to construct a novel tip structure. The aerodynamic characteristics of the tip leakage flow (TLF) with different blade tip configurations, such as the squealer, squealer-winglet (SW) and squealer-winglet-spontaneous injection holes (SWS) composite configurations, are numerically investigated. The impacts of several key geometric parameters, such as the winglet width and the space ng of spontaneous injection holes, are also discussed. Due to the adjustment of the winglet, the SW tip configuration can get better suppressing effect on TLF than the squealer tip. The SWS synergetic suppression tip decrease the leakage flow rate and the leakage mixing loss on the basis of the SW tip due to the blocking effect of the spontaneous injection flow. The key geometric parameters study shows that the suppressing effect of the TLF can be improved by reasonably increasing the winglet width and reducing the spacing between spontaneous injection holes.

Parametric Hypercell Mechanism for Adaptive Building Skin: A Case Study in New Administrative Capital, Egypt

The majority of the curtain wall (glazed) facades architectural proposals in the Middle East are double-skin facades with static structures such as utilizing the passive control method to respond to routine or normal conditions of weather. Nevertheless, the microclimate around the building changes dynamically and unpredictably. The study discusses, analyzes, and focuses on the role of designing dynamic parametric adaptive patterns in architecture. Therefore, the problem is how to use the methods of active control technology that could support more versatile interactive features to respond to the variance of climate conditions using parametric design software tools such as Rhino/Grasshopper programs that allow variable geometry to design the adaptive dynamic patterns to obtain thermal comfort inside buildings. The main objective of this study is to create a framework that provides a design strategy of a