Pulsed Suction Research Articles

Experimental study on pulsed suction under different momentum coefficients in variable compressor cascade with annular gaps

Variable Stator Vanes (VSVs) with penny cavities are crucial in the compressors of variable cycle engines, where complex interactions between annular and radial gaps can adversely affect aerodynamic performance. Unsteady active flow control techniques have significant potential for reducing secondary flow losses in compressors. This research investigates the internal flow characteristics of a variable compressor cascade with penny cavities using low-speed wind tunnel experiments and flow visualization techniques. This study is the first to experimentally explore the relationship between loss reduction and momentum coefficient using pulsed suction (PS) compared to steady continuous suction (SCS), evaluating the effects of various excitation frequencies. The findings show that at a momentum coefficient of 0.11 and an excitation frequency of 100 Hz, PS achieves optimal aerodynamic performance, reducing total pressure losses by 11.59 %, marking a 92.59 % improvement over SCS. As the momentum coefficient increases, the effectiveness of PS control significantly improves, whereas the changes in SCS effectiveness are less pronounced. The control effects of PS under varying excitation frequencies are complex and influenced by multiple factors. At higher momentum coefficients, the loss reduction effectiveness of PS is strongly correlated with excitation frequency, while at lower coefficients, performance changes due to frequency variations are minimal. This study provides valuable guidance for the design of modern multistage variable compressors.

Pulsed suction towards unsteady active flow control in an axial compressor cascade including clearance leakage effects

Tip leakage flow (TLF) induced by the gap between the stationary and rotating components brings complex flow structures, and this leads to a considerable loss in the compressor. Boundary layer suction is considered an efficient method to compensate the disadvantages brought by the TLF. In this study, the effect of hole-type pulsed suction (PS) on the TLF in a compressor cascade is investigated through a series of wind-tunnel experiment. PS is a more advanced technology over the constant suction (CS), and it considers improving of the compressor flow field from both spatial and frequency domain. The results indicate that the optimal aerodynamic performance is obtained when using PS at 25 % cx with a mass flow rate of 0.66 % and an excitation frequency of 100 Hz. First, flow control mechanisms are analyzed in terms of flow structures based on oil visualization and dynamic pressure results. The PS technique can induce significant periodic features and increase local intermittently momentum exchange. A connection between the local intensity of the excitation frequency and loss reduction at the cascade outlet is observed. Subsequently, the influence of the PS hole axial position is investigated, and the PS is found to contribute further control to the vortex structures than the CS. Finally, the effectiveness of the PS technique at different tip clearance sizes and inlet incidences is assessed to confirm its superiority over the CS technique in controlling TLF.

Active Flow Control Based Bleed in an Axial Compressor Cascade Using Large Eddy Simulation

The performance of the compressor is of great importance in developing advanced engine technology, and it dramatically influences the cycle efficiency and safety of the engine. The compressor bleed requires a part of the main flow extraction from the passage, and the removal of the airflow plays an essential role in the performance of the compressor. The influence of the constant suction and pulsed suction on the flow structures and the aerodynamic performance in a compressor cascade, and the control mechanisms are numerically studied using large eddy simulation. At a suction mass flow rate of 0.25% of the main flow rate, constant suction leads to a 9.36% reduction in Cpt, while pulsed suction gains 24% more benefit in Cpt reduction on the basis of the constant suction with an excitation frequency of 100 Hz. It indicates that the pulsed suction has more significant potential to control the loss generation in the compressor. Afterward, the flow field of the baseline, constant suction, and pulsed suction are compared to find out the flow control mechanisms of the constant suction and pulsed suction. Two different formation mechanisms of the passage vortex are found due to the excitation effect of the pulsed suction. Besides, the results of proper orthogonal decomposition and dynamic mode decomposition show that the pulsed suction can simplify and stabilize the compressor flow field, which could lead to a further benefit in Cpt.

Analysis of pulsed suction flow control behavior based on a nonlinear reduced-order model

The use of pulsed suction is an effective unsteady flow control method. However, compared with steady suction, which simply eliminates low-energy boundary layer, pulsed suction flow control presents unique phenomena and complex control mechanisms that are not explained fully. Thus, in this paper, pulsed suction flow control in a compressor cascade is investigated by numerical simulation. Numerical results show that the control performance depends on the suction frequency, momentum, and location, as any unsteady active flow control method. To further reveal the mechanism and explain the phenomena of pulsed suction, a nonlinear reduced-order model for pulsed suction flow control is established on the basis of the Navier–Stokes equation, Stuart vortex row model, Oseen vortex model, and Stuart–Landau equation. The entrainment degree and maximal Lyapunov exponent are used as indices to evaluate the flow losses and control performance in this model. By solving the equations of this model under different parameters, the model presents similar phenomena as found in the numerical simulations with various suction frequencies, momentum, and locations. Thus, it is innovative that the model with calibrated parameters has the ability to roughly predict control performance of unsteady pulsed suction in an efficient way. Also, based on this reduced-order model, one can explain that, unlike steady suction, chaos control, momentum transfer and lock-in mechanisms are especially relevant with the control physics of pulsed suction.

Pulsed Suction Control in a Highly Loaded Compressor Cascade With Low Suction Flowrates

Abstract The influence of pulsed suction (PS) on flow separation and aerodynamic performance in a highly loaded compressor cascade is experimentally studied herein. The excitation frequency is investigated as it determines the effectiveness of PS in flow control. Low suction flowrates are examined to analyze the potential of PS in providing a satisfactory cascade performance. For comparison, the corresponding parameters of steady continuous suction (SCS) are studied as well. Oil-flow visualizations and steady and unsteady pressure data are used to characterize the control effects of SCS and PS. The experimental results validate the efficacy of PS in controlling flow separation, even at a reduced suction flowrate of 0.1%. It suppresses passage vortex (PV), improving aerodynamic performance. PS provides a better control effect than SCS at different excitation parameters, which can be attributed to twofold main reasons: first, at the same suction flowrate, PS has a larger suction momentum than SCS during the suction phase, resulting in a stronger suction force and having a more profound effect on the flow characteristics; and second, owing to the introduction of pulsed excitation to the suction, PS creates additional vortex structures that energize the boundary layer by transporting high momentum freestream fluid near the wall. PS is also effective at a higher incidence angle, but its control effect is reduced.

A comparative experimental analysis of two unsteady flow control methods in a highly loaded compressor cascade

A comparative experimental analysis is performed on pulsed suction (PS) and pulsed blowing (PB) used to control flow separations in a highly loaded compressor cascade. The effectiveness of the control methods is assessed via oil-flow visualization and steady and unsteady pressure measurements. Firstly, the control effect of the PS is evaluated by comparing the conventional steady continuous suction (SCS). A more efficient control effect is achieved by the PS compared to the SCS. Additionally, in order to further explore the potentials of the PS and PB and gain some insight into their controlling mechanisms, some important excitation parameters including excitation location, momentum coefficient and frequency are comparatively investigated in detail. It is found that the PS and PB are both able to improve the cascade performance by effectively suppressing the passage vortex. With the excitation location moving downstream, the almost opposite change trends for the PS and PB on the total pressure loss and energy efficiency are shown. The PS has an advantage over the PB in improving the cascade performance at the same average excitation momentum. But there is a slighter change of the losses for the PB cases at different excitation frequencies relative to the PS ones, indicating that the PB is more insensitive to the excitation frequency. Based on the optimal excitation parameters, the total pressure loss coefficients for the PS and PB are reduced by 11.3% and 10.3%, respectively. Furthermore, the effectiveness of the PS and PB is also corroborated at a larger incidence angle.

Detailed Structure of the Skeleton, Muscles, and Connective-Tissue Elements in the Head of Silver Carp Hypophthalmichthys molitrix (Cyprinidae) in Relationship with the Functional Features of Its Visceral Apparatus

The structure of some muscles, ligaments, the aponeurotic system, and osteological traits of the visceral apparatus in silver carp Hypophthalmichthys molitrix is considered in detail. A number of the revealed traits of the jaw apparatus indicate its adaptation to pulsed suction filtration. The functional features of the feeding apparatus are analyzed based on the anatomical study and data published in literature.

Numerical Study of Unsteady Pulsed Suction through Endwall Bleed Holes in a Highly Loaded Compressor Cascade

Abstract Unsteady pulsed suction (UPS) was applied as an unsteady flow control (UFC) technique in a certain highly loaded compressor cascade to control the flow separations. Only two bleed holes symmetrically mounted on the endwalls (one on the upper endwall and another on the lower endwall) were set up to achieve steady constant suction (SCS) and UPS. The improvements in aerodynamic performance by SCS and UPS under different time-averaged suction flow rates are firstly investigated and compared. The related unsteady aerodynamic parameters of UPS such as excitation frequency, excitation location, pitch angle, and skew angle are discussed and analyzed in detail. The results show that UPS can provide a better flow control effect than SCS with the same time-averaged dimensionless suction flow rate in the control of flow separation. The aerodynamic performance of compressor cascades can be significantly enhanced by UPS when unsteady aerodynamic parameters are in their optimum ranges. Based on the optimum parameters for UPS, the total pressure loss coefficient is reduced by 19 % only with the time-averaged dimensionless suction flow rate ms =0.4 %.

A comparison of different unsteady flow control techniques in a highly loaded compressor cascade

A numerical research is applied to investigate the effect of controlling the flow separation in a certain highly loaded compressor cascade using different unsteady flow control techniques. Firstly, unsteady pulsed suction as a new novel unsteady flow control technique was proposed and compared to steady constant suction in the control of flow separation. A more exciting effect of controlling the flow separation and enhancing the aerodynamic performance for unsteady pulsed suction was obtained compared to steady constant suction with the same time-averaged suction flow rate. Simultaneously, with the view to further exploring the potential of unsteady flow control technique, unsteady pulsed suction, unsteady pulsed blowing, and unsteady synthetic jet (three unsteady flow control techniques) are analyzed comparatively in detail by the related unsteady aerodynamic parameters such as excitation location, frequency, and amplitude. The results show that unsteady pulsed suction shows greater advantage than unsteady pulsed blowing and unsteady synthetic jet in controlling the flow separation. Unsteady pulsed suction and unsteady synthetic jet have a wider range of excitation location obtaining positive effects than unsteady pulsed blowing. The ranges of excitation frequency and excitation amplitude for unsteady pulsed suction gaining favorable effects are both much wider than that of unsteady pulsed blowing and unsteady synthetic jet. The optimum frequencies of unsteady pulsed suction, unsteady pulsed blowing, and unsteady synthetic jet are found to be different, but these optimum frequencies are all an integer multiple of the natural frequency of vortex shedding. The total pressure loss coefficient is reduced by 16.98%, 16.55%, and 17.38%, respectively, when excitation location, frequency, and amplitude are all their own optimal values for unsteady pulsed suction, unsteady pulsed blowing, and unsteady synthetic jet. The optimum result of unsteady synthetic jet only slightly outperforms that of unsteady pulsed suction and unsteady pulsed blowing. But unfortunately, there is no advantage from the standpoint of overall efficiency for the optimum result of unsteady synthetic jet because the slight improvement has to require a greater power consumption than the unsteady pulsed suction and unsteady pulsed blowing methods.

Flow separation control using unsteady pulsed suction through endwall bleeding holes in a highly loaded compressor cascade

Unsteady pulsed suction (UPS) as a novel unsteady flow control (UFC) technique is applied in a certain highly loaded compressor cascade for the control of flow separations. Some related aerodynamic parameters such as excitation frequency and time-averaged suction flow rate are studied in detail. UPS and steady constant suction (SCS) are investigated to analysis comparatively the control effects of flow separations with the same time-averaged suction flow rate. The results show that UPS can provide appreciable improvement of cascade performance in a wide range of excitation frequencies. There are different optimum frequencies under different time-averaged suction flow rates, but the optimum frequencies are both an integer multiple of the natural frequency of vortex shedding. Based on the optimum frequency, the total pressure loss coefficients under the time-averaged suction flow rates ms=0.4% and ms=0.53% are reduced by 9.4% and 14.2%, respectively. The time-averaged suction flow rate plays a more crucial role than the excitation frequency. Simultaneously, UPS can provide a better flow control effect than SCS with the same time-averaged suction flow rate in the control of flow separation. The time-averaged suction flow rate range that can obtain positive effects for UPS is wider than that for SCS. Additionally, the potentials of UPS at off-design points are also validated.

Fluidic flow control applied for improved performance of Darrieus wind turbines

AbstractThe focus of the present research is performance enhancement of a vertical axis Darrieus‐type wind turbine using flow control techniques. The academic and industrial interest in vertical‐axis wind turbines (VAWTs) is increasing because of its suitability to urban areas, characterized by high turbulence and low wind speeds. The paper describes experimental work performed on a GOE222 asymmetrical airfoil intended to be used in a straight‐bladed Darrieus VAWT. Airfoil characteristics were measured in a wide range of incidence angles and Reynolds numbers, relevant for the operation of a small to medium size wind turbine. A variety of passive flow control (passive porosity and surface roughness) and active flow control techniques (boundary layer suction, pulsed suction) were tested in order to evaluate their effects on the airfoil performance. The measured effects of flow control on the 2D airfoil are integrated into a modified version of a double‐multiple streamtube model in order to predict the effects on the performance and efficiency of the turbine. It was found that the improvement of 2D airfoil characteristics can be translated into improvement of total turbine performance. By the use of active flow control, it was possible to increase the VAWT maximum mechanical output. When active flow control is properly activated taking into account the azimuth and Reynolds number conditioning, the effects could be greatly increased while consuming less energy, increasing the net efficiency of the entire system. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of disposable electronically pulsed lavage suction apparatus in wound cleansing

Objective To evaluate the clinical effect and safety of disposable electronically pulsed lavage suction apparatus in wound cleansing in a randomized single-blinded trial. Methods From April 2009 through January 2010, 51 patients were randomized into experimental and control groups. In the control group, wounds were debrided by flushing with normal saline directly. In the experimental group, wounds were cleansed with disposable electronically pulsed lavage suction apparatus. The clinical effects were evaluated in terms of inflammatory reaction and colony count around the wound 2 weeks after wound cleansing. Results All cases were followed up for 2 weeks. No significant differences were found between the 2 groups in the inflammatory reaction or in the colony count （4992 ± 19 640 vs. 21 000 ± 1 996 089） 2 weeks after wound cleansing （ P 〉 0. 05）. The wound effusion in the experimental group was signific.antly less than in the control group （x^2 = 4. 306, P = 0. 012）. In the experimental group, the colony count after wound cleansing （4992 ± 19 640） was significantly smaller than that before wound cleansing （423 000 ± 19 538 889） （ t = 10. 214, P = 0. 002） . No untoward reaction happened in this clinical trial. Conclusions Disposable electronically pulsed lavage suction apparatus is as effective and safe as the traditional method. Since the pulses lavage can decrease postoperative wound effusion and is convenient to use, it is recommendable in clinic. Key words: Irrigation; Surgical instruments; Debridemeut; Wounds and injuries

Ultrastructural evidence for thermal injury to pilosebaceous units during the treatment of acne using photopneumatic (PPX) therapy

Background and objective: Acne is a very prevalent skin disorder, and several devices, such as blue light, pulsed dye laser, diode laser, LED, RF and pulsed light systems, have been reported to have varying degrees of efficacy for treatment. Photopneumatic therapy (PPX) is a novel technology that combines pneumatic energy with a broadband light source to manipulate the optical characteristics of the skin. A vacuum suction raises target structures in the dermis closer to the surface of the skin prior to exposure, allowing for more efficient energy transmission. This study tested the hypothesis that a combination of pulsed light and suction would affect sebaceous plugging within diseased pilosebaceous apparati at a histological level, resulting in the rapid clearance of acne lesions. Methods: Eight individuals were treated with PPX once per week for a total of five treatments. Punch biopsies of the treated areas were obtained just after the first exposure, just before the third exposure and immediately after the fifth exposure. Those specimens were examined by conventional and by electron microscopy for any alterations following treatment. Results: Immediately following the first treatment, the mechanical extrusion of comedo contents from the infundibulum was observed histologically. One week after the second treatment, thermally injured bacteria as well as direct thermal injury to pilosebaceous apparati were observed ultrastructurally. Conclusion: These results correlate with clinical reports on decreased sebaceous gland activity after PPX treatment and may mechanistically give rise to the rapid regression of acne lesions.

Suction Thrombectomy of Thrombotic Occlusion of the Subclavian Artery in a Case of Takayasu’s Arteritis

Takayasu's arteritis, also known as pulseless disease, is a chronic inflammatory arteritis affecting large vessels, predominantly the aorta and its main branches. Vessel inflammation leads to wall thickening, fibrosis, stenosis, and thrombus formation. Percutaneous removal of arterial thrombus with the use of several devices has been reported, with mixed results. We present a case of Takayasu's arteritis with thrombotic occlusion of the subclavian artery in which pulsed urokinase injection and suction thrombectomy were used to revascularize a threatened limb and to establish the sole arterial supply to the brain.

SHORT COMMUNICATION

Abstract The purpose of this paper is to introduce new measurement techniques and configurations in gas suction pyrometry. A detailed description of three types of mini-pyrometers for the study of burning and heat transfer processes is presented. A suction pyrometer whose inner cavity is insulated by ceramic wool was developed for use in high velocity and high temperature jets of combustion products. A second type of pyrometer was developed for measuring oscillating gas temperatures, based on a micron-size sensitive head located in a spherical piece of fibrous material. through which the hot gases are aspirated. A third pyrometer was developed with an electrically-heated thermocouple and pulsed suction for use in low velocity “dirty” gaseous media.

The Pulsed Thermocouple for Gas Turbine Application

A mechanically pulsed suction thermocouple has been developed. The gas to be measured is sucked through a sonic orifice, thus eliminating the influence of the velocity inside the combustor. The signal from the thermocouple is processed by an analogue circuit. Contrary to the usual approach to the problem of dynamic temperature measurements (i.e., the attempt to find an exact solution to the extrapolation of the temperature rise curve) in this work, a calibration of the probe was done. This calibration showed very little scatter and a good repeatability. The overall measurement accuracy was better than ±1 percent. As a test of application, a partial survey of the temperature distribution within an aircraft gas turbine combustor was done. A satisfactory agreement was observed between temperatures measured by the thermocouple and those determined from gas analysis. In this test the pulse thermocouple proved to be a reliable and fast tool for the measurement of local gas temperatures.