scholarly journals Control of flow separation over a circular cylinder using synthetic jet

2021 ◽  
Vol 2119 (1) ◽  
pp. 012025
Author(s):  
A. S. Lebedev ◽  
M. I. Sorokin ◽  
D. M. Markovich
Keyword(s):  
Circular Cylinder ◽  
Flow Control ◽  
Flow Separation ◽  
Gas Turbines ◽  
Acoustic Noise ◽  
Reverse Flow ◽  
Flow Region ◽  
Synthetic Jet ◽  
Separation Flow ◽  
Longitudinal Length

Abstract The development of methods of active separation flow control is of great applied importance for many technical and engineering applications. Understanding the conditions for the flow separation from the surface of a bluff body is essential for the design of aircrafts, cars, hydro and gas turbines, bridges and buildings. Drag, acoustic noise, vibrations and active flow mixing depend drastically on the parameters of the vortex separation process. We investigated the possibility of reducing the longitudinal length of a reverse-flow region using the method of «synthetic jet» active separation flow control. The experiment was carried out on a compact straight-through wind channel with a 1-m long test section of a cross-section of 125x125 mm. The jet was placed at the rear stagnation point of a circular cylinder. The Reynolds number, based on the cylinder diameter and the free-stream velocity, was 5000 and the von Kármán street shedding frequency without the synthetic jet was equal to 64.8 Hz. For the first time, for such a set of parameters, we applied high speed PIV to demonstrate that the injection of the synthetic jet into the cylinder wake region leads to a significant reduction in the longitudinal length of the reverse-flow region.

Loss Mechanisms and Flow Control for Improved Efficiency of a Centrifugal Compressor at High Inlet Prewhirl

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Xinqian Zheng ◽  
Qiangqiang Huang ◽  
Anxiong Liu
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Flow Separation ◽  
Flow Instability ◽  
Reverse Flow ◽  
Leading Edge ◽  
Flow Region ◽  
Impeller Blade ◽  
Loss Mechanisms

Variable inlet prewhirl is an effective way to suppress compressor flow instability. Compressors usually employ a high degree of positive inlet prewhirl to shift the surge line in the performance map to a lower mass flow region. However, the efficiency of a compressor at high inlet prewhirl is far lower than that at zero or low prewhirl. This paper investigates the performances of a centrifugal compressor with different prewhirls, discusses the mechanisms which are responsible for the production of extra loss induced by high inlet prewhirl and develops flow control methods to improve efficiency at high inlet prewhirl. The approach combines steady three-dimensional Reynolds average Navier–Stokes (RANS) simulations with theoretical analysis and modeling. In order to make the study universal to various applications with inlet prewhirl, the inlet prewhirl was imposed by modifying the velocity direction of inlet boundary condition. Simulation results show that the peak efficiency at high inlet prewhirl is reduced by over 7.6% points compared with that at zero prewhirl. The extra loss occurs upstream and downstream of the impeller. Severe flow separation, which reduces efficiency by 2.3% points, was found near the inlet hub. High inlet prewhirl works like a centrifuge gathering low-kinetic-energy fluid to hub, which induces the separation. A dimensionless parameter C was defined to measure the centrifugal trend of gas and indicate the flow separation near the inlet hub. As for the extra loss which is produced downstream of the impeller, the flow mismatch of impeller and diffuser at high prewhirl causes a violent backflow near the diffuser vanes' leading edges. An analytical model was built to predict diffuser choking mass flow. It proves that the diffuser has already operated unstably at high prewhirl. Based on these two loss mechanisms, the hub curve and the diffuser stager angle were modified and adjusted, respectively, for higher efficiency at high prewhirl. The efficiency improvement benefited from the modification of the hub is 1.1% points, and that benefited from the combined optimization is 2.4% points. During optimizing, constant distribution of inlet prewhirl was found to be another factor for inducing reverse flow at the leading edge of the impeller blade root, which turned out being blamed on the misalignment of the swirl angle and the blade angle.

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

2018 ◽  
Vol 233 (6) ◽  
pp. 2051-2065 ◽  
Author(s):  
Hongxin Zhang ◽  
Shaowen Chen ◽  
Yun Gong ◽  
Songtao Wang
Keyword(s):  
Unsteady Flow ◽  
Flow Control ◽  
Flow Separation ◽  
Synthetic Jet ◽  
Control Technique ◽  
Compressor Cascade ◽  
Optimum Result ◽  
Control Techniques ◽  
Constant Suction ◽  
Highly Loaded

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.

Utilizing the L-PSJA for controlling cylindrical wake flow

2016 ◽  
Vol 26 (5) ◽  
pp. 1593-1616 ◽  
Author(s):  
Martin Skote ◽  
Imran Halimi Ibrahim
Keyword(s):  
Flow Control ◽  
Acoustic Noise ◽  
Control Device ◽  
Synthetic Jet ◽  
Wake Flow ◽  
Content Type ◽  
Synthetic Jet Actuator ◽  
Drag Forces ◽  
Flow Control Devices ◽  
Wake Turbulence

Purpose – The cylindrical wake flow is an important part of many engineering applications, including wake turbulence, acoustic noise, and lift/drag forces on bodies. The suppression of von Kármán vortex street (VKS) is an important goal for flow control devices. The paper aims to discuss these issues. Design/methodology/approach – The linear plasma synthetic jet actuator (L-PSJA) is utilized as a flow control device to suppress the VKS formation. Different configurations of the device is studied numerically. Findings – Of the 12 configurations that were investigated, five configurations were able to suppress the formation of the VKS. Originality/value – For the first time, the L-PSJA has been shown (through numerical simulations) to be able to suppress VKS.

Influence of Oscillating Boundary Layer Suction on Aerodynamic Performance in Highly-Loaded Compressor Cascades

2018 ◽  
Author(s):  
Xu Hao ◽  
Liu Bao ◽  
Cai Le ◽  
Zhou Xun ◽  
Wang Songtao ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vortex Shedding ◽  
Large Scale ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Flow Region ◽  
Flow Fields ◽  
Separation Flow ◽  
Oscillating Boundary ◽  
Pod Analysis

Vortex structures of the separation flow fields in compressor cascades controlled by the boundary layer oscillating suction (BLOS) are numerically investigated. The proper orthogonal decomposition (POD) method is adopted to present the variation of characteristics owned by large-scale vortices. It is found that unsteady perturbation re-organizes the aspirated flow fields and, if in a proper situation, reduces the loss furthermore. Through POD analysis, variations of vortical structures are described. The results turn out that the periodic perturbation leads to a vortex shedding process with the same frequency as the excitation. The reason of loss reduction could be summarized by actuated vortices enhancing the momentum of the stagnated fluid in the reverse flow region as well as decreasing the frequencies of vortex shedding. Finally, 3-D numerical results turn out that the oscillation can transform the stable corner separation bubble to vortex rings shedding downstream and hence improve cascade performance.

scholarly journals Flow Separation Control in a Curved Diffuser with Rigid Traveling Wave Wall and Its Mechanism

Energies ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 192 ◽  
Author(s):  
Weiyu Lu ◽  
Guoping Huang ◽  
Jinchun Wang ◽  
Yuxuan Yang
Keyword(s):  
Numerical Simulation ◽  
Flow Control ◽  
Flow Separation ◽  
Traveling Wave ◽  
Linear Stability Theory ◽  
Simplified Model ◽  
Separation Flow ◽  
Flow Separation Control ◽  
Fast Fourier Transform Analysis ◽  
Unsteady Separation

Traveling wave wall is a useful method to suppress flow separation. However, the interaction between the traveling wave wall and unsteady separation flow is complex, which causes difficulty in discovering the corresponding mechanism. To reveal the mechanism of traveling wave wall control, numerical simulation of a separated curved diffuser using rigid traveling wave wall flow control is performed, which shows some unique characteristics. Then, a nonlinear simplified model is used to explain this phenomenon in flow control in consideration of nonlinear dynamics and order of degree. Flow field data from the numerical simulation are further analyzed using fast Fourier transform analysis, linear stability theory of free shear layers, and the nonlinear simplified model to reveal the control mechanism of traveling wave wall.

Large-scale separation flow control on airfoil with synthetic jet

2018 ◽  
Vol 32 (2-3) ◽  
pp. 104-120 ◽  
Author(s):  
Z. L. Tang ◽  
J. D. Sheng ◽  
G. D. Zhang ◽  
J. Periaux
Keyword(s):  
Flow Control ◽  
Large Scale ◽  
Synthetic Jet ◽  
Separation Flow ◽  
Scale Separation

Turbulent Flow Over a NACA 4412 Airfoil at Angle of Attack 15 Degree

2003 ◽  
Author(s):  
O. O. Badran ◽  
H. H. Bruun
Keyword(s):  
Reverse Flow ◽  
Separation Bubble ◽  
Angle Of Attack ◽  
Flow Region ◽  
Shear Stresses ◽  
Separation Flow ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Trailing Edge ◽  
Short Period

This paper presents the measured mean flow and Reynolds stresses results, obtained on the center-line plane of the airfoil, covering the boundary layers over the upper surface, the potential flow region and the wake downstream of the trailing edge, at αa = 15°. The flying X-hot-wire probe was used to measure the U and V components of the flow field over the airfoil. An improved understanding of the physical characteristics of separation on the airfoil sections and in the region of the trailing edge is of direct value for the improvement of high lift wings for aircraft. From the study of the separation flow at angle of attack αa = 15°, the following can be concluded: (1) An intermittent reverse flow region occurred near the trailing edge of the airfoil. A separation bubble occurred for a short period of time and was then swept away with the stream wise flow. (2) The angle of attack αa = 15° corresponds to the position of maximum lift for a NACA 4412 airfoil section. (3) It is found that values of the Reynolds normal and shear stresses move away from the surface with downstream distance, and (4) In the wake region, relatively large values of Reynolds stresses occurred, which were related to the vertical oscillation in the lower wake.

Loss Mechanisms and Flow Control for Improved Efficiency of a Centrifugal Compressor at High Inlet Prewhirl

2015 ◽  
Author(s):  
Zheng Xinqian ◽  
Huang Qiangqiang ◽  
Liu Anxiong
Keyword(s):  
Flow Control ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Leading Edge ◽  
Flow Region ◽  
Percentage Points ◽  
Stable Conditions ◽  
Loss Mechanisms

Variable inlet prewhirl is an effective way to suppress compressor instability. Compressors usually employ a high degree of positive inlet prewhirl to shift the surge line in the performance map to a lower mass flow region. However, the efficiency of a compressor at high inlet prewhirl is far lower than that at zero or low prewhirl. This paper investigates the performances of a centrifugal compressor with different prewhirl, discusses the mechanisms thought to be responsible for the production of extra loss induced by high inlet prewhirl and develops flow control methods to improve efficiency at high inlet prewhirl. The approach combines steady three-dimensional Reynolds average Navier-Stockes (RANS) simulations with theoretical analysis and modeling. In order to make the study universal to various applications with inlet prewhirl, the inlet prewhirl was modeled by modifying the velocity condition at the inlet boundary. Simulation results show that the peak efficiency at high inlet prewhirl is reduced compared to that at zero prewhirl by over 7.6 percentage points. The extra loss is produced upstream and downstream of the impeller. Severe flow separation was found near the inlet hub which reduces efficiency by 2.3 percentage points. High inlet prewhirl works like a centrifuge gathering low-kinetic-energy fluid to hub, inducing the separation. A dimensionless parameter C is defined to measure the centrifugal component of flow. As for the extra loss produced downstream of the impeller, the flow mismatch of impeller and diffuser at high prewhirl causes a violent backflow near the diffuser vanes’ leading edges. An analytical model is built to predict diffuser choking mass flow which proves that the diffuser flow operates outside of stable conditions. Based on the two loss mechanisms, hub curve and diffuser stager angle were modified and adjusted for seeking higher efficiency at high prewhirl. The efficiency improvement of a modification of the hub is 1.1 percentage points and that of the combined optimization is 2.4 percentage points. During optimizing, constant distribution of inlet prewhirl was found to induce reverse flow at the leading edge of the blade root, which turned out being uncorrelated with blade angle. By revealing loss mechanisms and proposing flow control ideas, this paper lays a theoretical basis for overcoming the efficiency drop induced by high inlet prewhirl and for developing compressors with high inlet prewhirl.

Effect of Unsteady Wake on Flow Control of the Low-Pressure High-Lift Cascade with Synthetic Jet

2012 ◽  
Vol 588-589 ◽  
pp. 1790-1793
Author(s):  
Yong Hui Xie ◽  
Huan Cheng Qu ◽  
Hai Yu He
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Flow Separation ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Synthetic Jet ◽  
High Lift ◽  
Eddy Simulation ◽  
Unsteady Wake ◽  
Large Eddy

The flow separation is susceptible to appear and is known to affect the aerodynamic performance of the low-pressure high-lift cascade. Large Eddy Simulation was adopted in the present work and the periodic moving bar was employed to simulate the unsteady wake upstream of the blade. The flow control of the synthetic jet with unsteady wake was investigated in detail. The upstream wake increased the turbulent level of the boundary layer of the cascade. The synthetic jet got a better control under the effect of the upstream wake.

Sign in / Sign up

Export Citation Format

Share Document