Suction Flow Control Research Articles

Quantitative study on the flow control of a 1:2 rectangular cylinder based on the leading-edge suction

The present study employed the leading-edge suction flow control on a 1:2 rectangular cylinder to control its unsteady aerodynamics. To study the suppression on aerodynamic forces, the surface pressures were measured at the Reynolds number of 1.28 × 104. A dimensionless suction momentum coefficient (Cμ) was defined to quantify the suction flow rate. The detailed flow visualization was conducted on the wake flows as well as the leading-edge separated flows to reveal the control mechanism. The proper orthogonal decomposition (POD) analysis was conducted on the wake flows to study the modal transformations. Results show that the leading-edge suction flow control could significantly affect the flow separation-reattachment characteristics and the present control processing could be divided into five stages with increasing Cμ. The lift fluctuation could reach a maximum reduction of 66.4%. Meanwhile, the flow separation at the leading edge was gradually suppressed and eliminated with increasing Cμ. The wake flow was compressed in the transverse region and suppressed in the turbulent kinetic energy (TKE) as well as the Reynolds shear stress (RSS), which should be responsible for the suppression on the lift fluctuation.

Comparative study of two combined blowing and suction flow control methods on pitching airfoils

A comparative study of two combined blowing/suction flow control methods was conducted on the pitching airfoil using the unsteady Reynolds-averaged Navier–Stokes (URANS) method. One used leading-edge blowing and trailing-edge suction, which is referred to as a co-flow jet (CFJ), and a conformal slot CFJ (C-CFJ) was adopted. Another used leading-edge suction combined with trailing-edge blowing, which was called reversed CFJ (R-CFJ). The S809 airfoil was used as the baseline as its stall characteristic is suitable for separation flow or stall control research. Aerodynamic coefficients of these two combined blowing/suction methods were compared under no-stall, mild-stall, and deep-stall cases. The net gain of output power was also discussed if CFJ methods were used for wind energy applications. The influence mechanism of these two methods on the flow around the airfoil was revealed. The results showed that the C-CFJ is suitable for the no-stall and mild-stall cases, while the R-CFJ is suitable for the deep-stall case. Leading-edge suction is more stable than leading-edge blowing when suppressing the dynamic stall. The leading-edge jet flow will cause dynamic stalls when it is detached from the airfoil surface, while the detached jet flow can block the development of the separation when it is placed on the trailing edge.

Receptivity-orientated drag reduction of twin cylinders by steady leading-edge suction control based on adjoint method

This study investigates the drag reduction of two tandem square cylinders under steady suction control at Reynolds numbers 50–200. The position where the suction flow should be placed is determined by using a receptivity analysis based on the adjoint method, and we investigate how control affects the fluid force and flow structures. High-order dynamic mode decomposition (HODMD) is applied to analyze the dynamic coherence modes and uncover the underlying control mechanism. The adjoint modes show that the regions of maximum receptivity to momentum forcing are localized on each side of the up-cylinder (UC) near the leading edge (LE). Thus, the suction flow is placed on the LE. The drag can be significantly reduced at wide gap distances, especially for the co-shedding regime. Under suction flow control, the separation is suppressed near the LE, and the gap vortices are no longer fed by the vorticity generated by the separated shear layer; they only result from the trailing-edge separation, which weakens and shrinks. Subsequently, the interaction between the gap flow and the down-cylinder (DC) is weakened, which reduces the drag and lift forces. The decrease in drag exceeds 66.4% for the UC and reaches 81.6% for the DC. The fluctuating reduction in the lift for the UC (DC) exceeds 59.0% (75.7%). HODMD results show that, as the suction flow velocity increases, the LE suction flow modifies the local time-averaged modes rather than the global mode energy. Conversely, the dynamic mode energy decreases significantly, whereas the mode shape remains unchanged except for a phase shift.

Greedy Non-Intrusive Reduced-Order Model’s application in dynamic blowing and suction flow control to suppress the flow separation

The Greedy Non-Intrusive Reduced-Order Model (GNIROM) is applied in dynamic blowing and suction’s flow control to suppress the GAW1 airfoil’s flow separation. The effects of the uniform blowing and uniform suction on the flow fields and aerodynamic coefficients have been studied firstly. By comparing a uniform suction control with a dynamic blowing and suction control, it has been found that the dynamic blowing and suction can provide a higher lift coefficient and a lower energy loss. Finally, for the sake of achieving an optimal dynamic blowing and suction control, an optimization of the dynamic blowing and suction’s parameters is taken based on the GNIROM, consisting of a Non-Intrusive ROM (NIROM) built by the two-level POD and Radial Basis Function (RBF), and the relative greedy method. A cost function has been proposed by considering suppressing the flow separation, improving the lift-drag characteristics and reducing the energy loss together. The GNIROM has been built for unsteady vorticity fields with the parameters of the dynamic blowing and suction varying. Based on the GNIROM’s approximation, the optimal control parameters’ values have been determined quickly. Compared to the initial dynamic blowing and suction control, the optimal one has reduced the drag coefficient by 43.4 percents and the energy loss by 42 percents.

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.

Investigation of Suction Flow Control on Centrifugal Compressor with Vaned Diffuser

In this study, the effect of suction flow control on a centrifugal compressor at operation and stall flow rates was investigated using computational fluid dynamics (CFD). The compressor geometry was reconstructed from available open source profile data and the CFD analyses have been performed on this geometry using the appropriate mesh. To validate the CFD results, the compressor performance line was acquired and compared with the experimental results obtained at the design rotational speed. Then, suction flow control was employed at various suction slot positions with different suction flow rates to improve the performance of the compressor at operation and stall flow rates. As a result of the suction flow control trials, 0.85% increase in pressure ratio and 0.8% increase in adiabatic efficiency were achieved while the compressor was running at operation flow rate. The performance improvements corresponding to the stall flow rate of the compressor were 2.5% increase in pressure ratio and 2% increase in adiabatic efficiency.

Influence of suction flow control on energy extraction characteristics of flapping foil

ABSTRACT Flapping foil (FF) is a relatively new renewable energy extraction device, which has the advantages of simple structure, strong environmental adaptability and little impact on the environment. This study proposed a new FF energy extraction equipment with suction control added to the surface. Based on the moving grid technology, the effect of different suction control methods on energy extraction characteristics of FF was numerically investigated. In this paper, taking NACA0012 as the reference airfoil, the influence laws of key parameters, such as suction velocity, suction port position and suction mode on the energy extraction efficiency of FF were studied respectively. The results show that, compared with the original FF, the addition of suction control can effectively control the size of the leading edge negative effect vortex, increase the force consistent with the motion direction of the FF and its surface pressure difference, thus improving the energy extraction efficiency. In addition, the innovative change of suction mode to sinusoidal suction mode in this paper can not only enhance the stability and safety of FF operation structure, but also its energy extraction efficiency is not much different from that of FF with sudden suction control.

Control of the oscillations of shock train using boundary layer suction

The isolator plays a major role in the scramjet engine by providing suitable pressure for the combustion process. It is situated between the inlet and the combustion chamber. The deceleration of supersonic flow into subsonic flow is achieved by a series of bifurcated normal shock waves referred to as “shock train”. The flow field is more complex with shock–shock interaction and shock boundary layer interaction. The presence of such flow inside the isolator can degrade the performance of the scramjet engine. The present study focuses on the self-excited shock train flow in an isolator and its control by partial removal of the boundary layer. The results examine the variation of the inlet to outlet pressure ratio with and without suction flow control. Numerical results indicate that the boundary layer suction will cause downstream movement of the shock train and the length of the shock train is reduced. The transformation of the shock train into a single curved normal shock is observed when the shock train present closer or upstream of the suction slot region. The obtained result shows the self-excited oscillation frequency in the range of 14-15 Hz. The suction control provides an advantage by 50% reduction in the amplitude of the shock train movement.

Aerodynamic drag reduction on the application of suction flow control on vehicle model with varied upstream velocity

The innovation in the automotive industry must prioritize the issue of energy security and the environment. One aspect of the innovations is regarding the development of more aerodynamic vehicle design. The study of vehicle aerodynamics has been considered as very important, due to its direct relation to the safety and efficiency factors of energy utilization. Applying active control on the onset region of flow separation is one example of the efforts. This study aims to analyse the effect of the application of active control by suction to the aerodynamic drag of the vehicle model through qualitatively observations of flow dynamics and quantitatively pressure fields. The test model is a modified Ahmed body with 35° slant angles and varied flow orientations. This study has been conducted in both numerical computation and experimental testing at a suction velocity of 1.0 m/s and upstream velocity of 11.1 m/s, 13.9 m/s, and 16.7 m/s, respectively. The results have found out that the attachment of active control is proven capable able to delay flow separations, to increase the pressure coefficients on the back wall, and to reduce aerodynamic drag by 10.8487% for computational methods and 10.9748% for experimental methods.

Experimental and numerical simulations of simple frigate with suction flow control over the deck

The air wake generated behind a frigate superstructure is a very complex and unsteady three-dimensional flow characterized by highly turbulent flow structures with great velocity gradients that result in flow separation over the flight deck where helicopter operations take a significant role. Naturally, this turbulent flow should be removed or, at least, reduced as maximum as possible to avoid accidents during the interaction between frigates and helicopters. This paper involves experimental and numerical analysis on a simple frigate model (SFS2) to understand and simulate the adverse effect of the turbulent flow of the air wake over the deck and tries to minimize it as with active flow control. The experimental study has been performed in the Low Speed Wind Tunnel nº1 of Instituto Nacional de Técnica Aeroespacial ‘‘Esteban Terradas'’ (INTA) with Particle Image Velocimetry (PIV) to obtain the velocity field over the flight deck. The frigate has been tested for the headwind condition of 0° (wind aligned with the flight deck) with a velocity of 10 m/s. The active flow control consists on generating suction on the flight deck by a mesh of holes. Several configurations of this suction mesh have been studied according to the diameter and location of holes and suction intensity. The suction mesh configuration with the highest diameter and flow rate presents the greatest aerodynamic improvement. The low-speed area over the deck is reduced from 36% to a minimum of 3%.

Numerical study of the suction flow control of the supersonic boundary layer transition in a framework of gas-kinetic scheme

In this paper, we numerically study the supersonic boundary layer transition process and the suction flow control method by employing the DNS technology. By adopting the high resolution GKS method, the mechanism of the boundary transition and the statistical characteristics of the compressible turbulent boundary layer are investigated. Results indicate that the streamwise vortex and the three-dimensional shear layer with high instability are the main causes of the boundary layer transition. Suction control cases show that the laminar boundary layer suction can weaken the development of the unstable disturbance waves in the boundary layer, and delay the streamwise position of the local disturbance. Also, the space distributions of the vortex structure are weakened to delay the process of the transition.

Blowing–Suction Control in S-Shaped Inlet and Its Impact on Fan-Stage Performance

This paper presents a numerical investigation of flow control with blowing and suction in the whole structure consisting of an aggressive S-shaped air intake accompanied by a downstream fan stage. The results show that the effect of blowing–suction flow control is neither the simple summation of the effects of a single blowing control and a suction control nor the simple differences between them. It is the best one among three flow control techniques studied in this paper. The approach to selecting the optimum flow control scheme via simulating the single air intake, and afterward performing the numerical simulation of whole passage, has a certain rationality. With the blowing–suction flow control, the maximum isentropic efficiency and maximum total pressure ratio of the fan stage increase by 2.70 and 3.13%, respectively. Moreover, the rotor of the fan stage has a significant effect in reducing circumferential distortions. Due to the influence of the rotating fan rotor, the low-energy region at the lower side of the cross sections decreases gradually when approaching the fan-stage inlet. The low-energy fluid always exists in several blade passages after it enters the fan stage. Using the blowing–suction flow control, the relative total pressure of fluid in these low-energy passages increases to an extent. Streamlines in the fan stator flow passages and on stator blades show that the blowing–suction flow control in the air intake can improve the fan stator flow pattern, reducing the flow separation in general.

On the Active and Passive Flow Separation Control Techniques over Airfoils

In the present work, recent advances in the field of the active and passive flow separation control, particularly blowing and suction flow control techniques, applied on the common airfoils are briefly reviewed. This broad research area has remained the point of interest for many years as it is applicable to various applications. The suction and blowing flow control methods, among other methods, are more technically feasible and market ready techniques. It is well established that the uniform and/or oscillatory blowing and suction flow control mechanisms significantly improve the lift-to-drag ratio, and further, postpone the boundary layer separation as well as the stall. The oscillatory blowing and suction flow control, however, is more efficient compared to the uniform one. A wide range of parameters is involved in controlling the behavior of a blowing and/or suction flow control, including the location, length, and angle of the jet slots. The oscillation range of the jet slot is another substantial parameter.

Suction and Blowing Flow Control on Airfoil for Drag Reduction in Subsonic Flow

Lift force is produced from a pressure difference between the pressures acting in upper and lower surfaces. Therefore, flow becomes detached from the surface of the airfoil at separation point and form vortices. These vortices affect the aerodynamic performance of the airfoil in term of lift and drag coefficient. Therefore, this study is investigating the effect of suction and jet blowing in boundary layer separation control on NACA 0012 airfoil in a subsonic wind tunnel. The experiment examined both methods at the position of 25% of the chord-length of the airfoil at Reynolds number 1.2 × 105. The findings show that suction and jet blowing affect the aerodynamic performance of NACA 0012 airfoil and can be an effective means for boundary layer separation control in subsonic flow.

Experimental Study of Suction Flow Control Effectiveness in a Serpentine Intake

The intakes of modern aircraft are subjected to ever-increasing demands in their performance. Particularly, they are expected to carry out diffusion with the highest isentropic efficiency while subjected to aggressive geometry requirements arising from stealth considerations. To avoid a penalty in engine performance, the flow through intake needs to be controlled using various methods of flow control. In this study, a serpentine intake is studied experimentally and its performance compared with and without boundary layer suction. The performance parameters used are nondimensional total pressure loss coefficient and standard total pressure distortion descriptors. The effect is observed on surface pressure distributions, and inferences are made regarding separation location and extent. A detailed measurement at the exit plane shows flow structures that draw attention to secondary flows within the duct. Suction is applied at three different locations, spanning different number of ports along each location, comprising of ten unique configurations. The mass flow rate of suction employed ranges from 1.1% to 6.7% of mass flow rate at the inlet of the intake. The effect is seen on exit total pressure recovery as well as circumferential and radial distortion parameters. This is examined in the context of the location of the suction ports and amount of suction mass flow, by the deviation in surface pressure distributions, as well as the separation characteristics from the baseline case. The results show that applying suction far upstream of the separation point together with a modest amount of suction downstream results in the best performance.

Research of the suction flow control on wings at low Reynolds numbers

Laminar separation and transition have significant effects on aerodynamic characteristics of the wing under the condition of low Reynolds numbers. Using the flow control methods to delay and eliminate laminar separation has great significance. This study uses the method combined with water tunnel test and numerical calculation to research the effects of suction flow control on the flow state and aerodynamic force of the wing at low Reynolds numbers. The effects of suction flow rate and suction location on laminar separation, transition and aerodynamic performance of the wing are further researched. The results of the research show that, the suction can control laminar separation and transition effectively, when the suction holes are in the interior of the separation bubble, and close to the separation point, the suction has the best control effect. When the Reynolds number is Re = 3.0 × 105, the suction flow control can make the lift-to-drag ratio of the wing increase by 8.62%, and the aerodynamic characteristics of the wing are improved effectively.

Three-dimensional suction flow control and suction jet length optimization of NACA 0012 wing

A three-dimensional suction flow control study was performed to investigate the aerodynamic characteristics of a rectangular wing with a NACA 0012 airfoil section. In addition, the optimum suction jet length was determined. In this study, the Reynolds-averaged Navier–Stokes equations were employed in conjunction with a k–ω SST turbulent model. Perpendicular suction was applied at the leading edge of the wing’s upper surface, with two different types of slot distributions: i.e., center suction and tip suction. The suction jet lengths were varied by 0.25–2 of the chord length, and the jet velocity was selected to be 0.5 times the freestream velocity. Most importantly, in both cases, the results indicated that the lift-to-drag ratio increased as the suction jet length rose. However, the improvement in aerodynamic characteristics was more pronounced with center suction, and these characteristics were extremely close to those of the case considering suction over the entire wing such that the jet length was equal to wingspan. Moreover, in the center suction case, vortexes frequently abated or moved downstream. Interestingly, under similar conditions, a greater number of vortexes were removed with center suction than with tip suction. Ultimately, when the jet length is less than half the wingspan, tip suction is the better of the two alternatives, and when the jet length is greater than half the wingspan, center suction is better suited.

Numerical study of blowing and suction slot geometry optimization on NACA 0012 airfoil

The effects of jet width on blowing and suction flow control were evaluated for a NACA 0012 airfoil. RANS equations were employed in conjunction with a Menter’s shear stress turbulent model. Tangential and perpendicular blowing at the trailing edge and perpendicular suction at the leading edge were applied on the airfoil upper surface. The jet widths were varied from 1.5% to 4% of the chord length, and the jet velocity was 0.3 and 0.5 of the free-stream velocity. Results of this study demonstrated that when the blowing jet width increases, the lift-to-drag ratio rises continuously in tangential blowing and decreases quasi-linearly in perpendicular blowing. The jet widths of 3.5% and 4% of the chord length are the most effective amounts for tangential blowing, and smaller jet widths are more effective for perpendicular blowing. The lift-to-drag ratio improves when the suction jet width increases and reaches its maximum value at 2.5% of the chord length.

An experimental study on a suction flow control method to reduce the unsteadiness of the wind loads acting on a circular cylinder

An experimental investigation was conducted to assess the effectiveness of a suction flow control method for vortex-induced vibration (VIV) suppression. The flow control method uses a limited number of isolated suction holes to manipulate the vortex shedding in the wake behind a circular cylinder in order to reduce the unsteadiness of the dynamic wind loads acting on the cylinder. The experimental study was performed at Re ≈ 3.0 × 104, i.e., in the typical Reynolds number range of VIV for the cables of cable-stayed bridges. In addition to measuring the surface pressure distributions to determine the resultant dynamic wind loads acting on the test model, a digital particle image velocimetry system was used to conduct detailed flow field measurements to reveal the changes in the shedding process of the unsteady wake vortex structures from the test model with and without the suction flow control. The effects of important controlling parameters (i.e., the azimuthal locations of the suction holes in respect to the oncoming airflow, the spanwise spacing between the suction holes, and the suction flow rate through the suction holes) on the wake flow characteristics, the surface pressure distributions, and the resultant dynamic wind loads were assessed quantitatively. While a higher suction flow rate and smaller spanwise spacing between the suction holes were beneficial to the effectiveness of the suction flow control, the azimuthal locations of the suction holes were found to be very critical for reducing the fluctuating amplitudes of the dynamic wind loads acting on the test model using the suction flow control method. With the suction holes located at the proper azimuthal locations on the test model (i.e., at the azimuthal angle of θ = 90° and 270° for the present study), the characteristics of the wake flow behind the test model were found to change significantly along the entire span of the test model, even though only a limited number of the isolated suction holes were used for the suction flow control. The detailed flow field measurements were correlated with the measured surface pressure distributions and the resultant dynamic wind loads acting on the test model to gain further insight into the fundamental mechanism of the suction flow control method for VIV suppression.

Suction and Pulsed-Blowing Flow Control Applied to an Axisymmetric Body

A flow-control study using steady suction and pulsed blowing in close proximity was conducted on an axisymmetric bluff body at length-based Reynolds numbers between 1.0 and . The study included a coupled incremental computational-fluid-dynamics and experimental approach. It began with computations of various model setup designs. Subsequently, flow-control experiments and computations were used to optimize steady suction alone. Finally, flow control was provided by a synchronized array of 28 suction and oscillatory blowing actuators, positioned slightly upstream of the baseline separation. Results show suction alone has a limited ability to delay separation and reduce drag on this geometry. Suction located far from the baseline separation is shown to actually increase drag. Addition of pulsed blowing enables separation delay to the trailing edge and drag to be nullified. Increased overall system efficiency, including estimated total actuator power invested, was found at low momentum input for optimally located steady suction and pulsed blowing. This was partially attributed to the particular geometry used because the active flow-control system shows a robust ability to delay separation. Not all measured trends were predicted by computation due to the complex nature of this configuration and the active flow-control system characteristics.