Evaporator Superheat Regulation via Emulation of Semi-Active Flow Control

2009 ◽  
Author(s):  
Matthew Elliott ◽  
Bryan P. Rasmussen
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Control Device ◽  
Operating Conditions ◽  
Limiting Factor ◽  
Efficient Operation ◽  
Control Approach ◽  
Active Feedback ◽  
Vapor Compression Cooling ◽  
Active Flow

Proper regulation of evaporator superheat is essential to ensuring safe and efficient operation of vapor compression cooling systems. Typical mechanical control devices may behave poorly under transient disturbances or as operating conditions vary, degrading system performance. Electronic expansion valves partially alleviate these problems by allowing more sophisticated control approaches, but frequent valve adjustments raise concerns about device longevity. A cascaded control approach to superheat regulation has been shown to provide significant improvements in superheat control, utilizing a hybrid of mechanical (passive) and electronic (active) feedback devices. This paper examines the emulation of a semi-active flow control device using a MEMs based actuator with high bandwidth, few moving parts, and no risk of fatigue failure. Experimental evaluation reveals this to be a comparable approach to the hybrid valve design. Moreover, further examination reveals that actuator characteristics are the limiting factor in achieving similar levels of performance using standard electronic valves.

Active Flow Control Utilizing an Adaptive Blade Geometry and an Extremum Seeking Algorithm at Periodically Transient Boundary Conditions

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
Tobias Werder ◽  
Robert Liebich ◽  
Karl Neuhäuser ◽  
Clara Behnsen ◽  
Rudibert King
Keyword(s):  
Phase Shift ◽  
Flow Control ◽  
Gas Turbines ◽  
Active Flow Control ◽  
Operating Conditions ◽  
Extremum Seeking ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Active Flow ◽  
The Impact

Abstract As a consequence of constant volume combustion in gas turbines, pressure waves propagating upstream the main flow into the compressor system are generated leading to incidence variations. Numerical and experimental investigations of stator vanes have shown that active flow control (AFC) by means of adaptive blade geometries is beneficial when such periodic incidence variations occur. A significant risk reduction in a compressor facing disturbances can thereby be achieved concerning stall or choke. Experimental investigations on such an AFC method with simultaneous application of a closed-loop control are missing in order to demonstrate its potential. This work investigates a linear compressor cascade that is equipped with a 3D-manufactured piezo-adaptive blade structure. The utilized actuators are piezoelectric macro-fiber-composites. A throttling device is positioned downstream the trailing edge plane to emulate an unsteady combustion process. Periodic transient throttling events with a frequency of up to 20 Hz cause incidence changes to the blade’s leading edge. Consequently, pressure fluctuations on the blade’s surface occur, having a significant impact on the pressure recovery downstream of the stator cascade. Experimental results of harmonically actuating the piezo-adaptive blade with the corresponding disturbance frequency show that the impact of disturbances can be reduced to approximately 50%. However, this is only effective if the phase shift of the harmonic actuation is adjusted correctly. Using an inadequate phase shift reverses the positive effects, causing the aforementioned stall, choke, or significant losses. In order to find the optimum phase shift, even under varying, possibly unpredictable operating conditions, an extremum seeking controller is presented. This gradient-based approach is minimizing the pressure variance over time by carefully adjusting the phase shift of the harmonic actuation of the AFC system.

Experimental study on an airfoil equipped with an active flow control element

2021 ◽  
pp. 0309524X2110667
Author(s):  
Dominik Hochhäusler ◽  
Gareth Erfort
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Vertical Axis ◽  
Torque Ripple ◽  
Control Device ◽  
Survey Method ◽  
Control Element ◽  
Data Set ◽  
Reduction Error ◽  
Active Flow

This paper addresses the torque ripple problem of vertical axis wind turbines (VAWT) by applying an oscillating bump which was previously optimised with a numerical model. Since the element primarily affects the drag of an airfoil, a low-speed wind-tunnel experiment using the wake survey method was conducted in order to highlight the effect on the drag of a symmetrical airfoil. Measurements were taken along the centreline of the foil to compare with numerically simulated results on a 2D foil. This study provides an experimental data set for an active flow control device. When the stationary results were compared against numerical simulation they showed an overall good agreement. The moving bump increased the drag coefficient for higher frequencies of oscillation and induced less drag compared to the steady maximum distortion. Uncertainties in the experiments were primarily caused by fluctuations in the test section and the data reduction error. Future work should include the measurement of lift in order to determine the influence of the element on the torque.

LES of Active Separation Control on Bluff Bodies by Steady Blowing

2010 ◽  
Author(s):  
Sa´ndor Eichinger ◽  
Frank Thiele ◽  
Erik Wassen
Keyword(s):  
Flow Control ◽  
Aerodynamic Drag ◽  
Active Flow Control ◽  
Rear Surface ◽  
Base Flow ◽  
Back Surface ◽  
Bluff Bodies ◽  
Control Approach ◽  
Vertical Extension ◽  
Active Flow

An active flow control approach was investigated in order to reduce the aerodynamic drag of a generic square-backed vehicle. The investigations were carried out at a Reynolds number of ReL = 500,000. Large Eddy Simulations were performed which are suitable for time dependent flows around vehicles with large coherent structures. After the base flow simulations active flow control was applied in order to achieve drag reduction using steady blowing through small slits near the edges of the rear surface. The blowing velocity was equal to the inflow velocity (vblow = U0), and the blowing angle was changed from θ = 0° to θ = 60°. It is shown that these control techniques can achieve a maximum drag decrease for the θ = 45° control version of around 12%. Additionally the effect of moving floor was studied and comparison was made for the baseline and for the 45° flow control variant. It was found that the stagnation point on the rear surface moves upwards, and the vertical extension of the wake section reduces, so the evolving pressure level on the back surface increases. Finally a study of the blowing velocity was performed, changing vblow = 0.25U0 until vblow = 2.25U0 at θ = 45° blowing angle. An efficiency optimum was found around vblow = 1.25U0.

Numerical Simulation of Unsteady Flow around Ahmed Body with Active Flow Control

2013 ◽  
Vol 275-277 ◽  
pp. 402-408
Author(s):  
Bing Xin Wang ◽  
Zhu Hui ◽  
Zhi Gang Yang
Keyword(s):  
Flow Control ◽  
Recirculation Zone ◽  
Active Flow Control ◽  
The Body ◽  
Slant Angle ◽  
Control Approach ◽  
Pressure Drag ◽  
Active Flow ◽  
Velocity Pressure ◽  
Ahmed Body

The numerical investigations presented in this paper deal with active flow control approach at the rear end of the Ahmed body model with the slant angle of 25°.Results of the velocity, pressure and vorticity field demonstrate the main reasons that cause the pressure drag. The influence of the spanwise and streamwise vortices rolling up from the slant and the edges on the recirculation zone behind the body is examined. A control slot is set on the separated line at the conjunction of the roof and the slant. Two different actuation concepts by blowing and suction steady jets through the slot lead to a drug increase of 5.61% and a drug reduction of 13.20% with the efficiency of 12.53% respectively.

In-sewer sedimentation associated with active flow control

2009 ◽  
Vol 60 (1) ◽  
pp. 55-63 ◽  
Author(s):  
K. J. Williams ◽  
S. J. Tait ◽  
R. M. Ashley
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Control Device ◽  
Fine Material ◽  
Sewer Systems ◽  
Gate Opening ◽  
Flow Control Device ◽  
Upstream Direction ◽  
Active Flow ◽  
Large Sections

Active flow control using automated gates and weirs aims to utilise available dispersed storage within sewer systems to alleviate the severity and frequency of localised flooding incidents. Whilst a previous study has demonstrated its potential, a key operational concern before implementation was sedimentation. An experimental programme was designed to investigate the sediment deposition created when using a flow control device. Tests were also undertaken to examine the potential for rapid gate opening to flush away any resulting deposits. In catchments dominated by fine material in suspension, the use of an active flow control device can result in a uniformly thick deposit upstream of the gate. Rapid gate opening results in deposited material eroding in large sections starting at the gate and moving in an upstream direction. Granular sediment forms a series of discrete bedforms which are fairly uniform regardless of the flow conditions and a larger deposit further upstream. The potential for flushing granular deposits is limited and modification of the operation of the gate has shown little potential for increasing the effectiveness. Therefore, active flow control using a single downstream gate may only be suitable in systems with fine material moving in suspension during dry weather flow and not where there is significant granular sediment.

scholarly journals Active Flow Control of a Pump-Induced Wall-Normal Vortex With Steady Blowing

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Qiong Liu ◽  
Byungjin An ◽  
Motohiko Nohmi ◽  
Masashi Obuchi ◽  
Kunihiko Taira
Keyword(s):  
Flow Control ◽  
Structural Damage ◽  
Active Flow Control ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Slip Boundary Condition ◽  
Control Technique ◽  
Control Approach ◽  
Slip Boundary ◽  
Active Flow

Abstract The emergence of a submerged vortex upstream of a pump can reduce pump intake efficiency and cause structural damage. In this study, we consider the use of active flow control with steady blowing to increase the pressure distribution within a single-phase pump-induced wall-normal vortex model, which is based on the Burgers vortex with a no-slip boundary condition prescribed along its symmetry plane. The goal of our control is to modify the vortex core velocity profile. These changes are sought to increase the core pressure such that detrimental effects on the pump are alleviated. Three-dimensional direct numerical simulations are performed to examine the dynamics of the vortex with the application of axial momentum injection at and around the root of the vortex. We find that the active flow control approach can effectively modify the wall-normal vortical structure and significantly increase the low-core pressure by up to 81% compared to that of the uncontrolled case. The result shows that the control setup is also effective when it is introduced in an off-centered manner. Compared to the unsteady blowing and suction-based actuation from our previous work (Liu, Q., An, B., Nohmi, M., Obuchi, M., and Taira, K., 2018, “Core-Pressure Alleviation for a Wall-Normal Vortex by Active Flow Control,” J. Fluid Mech., 853, p. R1.), the current steady control technique offers an effective and simple flow control setup that can support robust operations of pumps.

Active Flow Control Utilizing an Adaptive Blade Geometry and an Extremum Seeking Algorithm at Periodically Transient Boundary Conditions

2020 ◽  
Author(s):  
Tobias Werder ◽  
Robert Liebich ◽  
Karl Neuhäuser ◽  
Clara Behnsen ◽  
Rudibert King
Keyword(s):  
Phase Shift ◽  
Flow Control ◽  
Gas Turbines ◽  
Active Flow Control ◽  
Operating Conditions ◽  
Extremum Seeking ◽  
Experimental Investigations ◽  
Compressor Cascade ◽  
Active Flow ◽  
The Impact

Abstract As a consequence of constant volume combustion in gas turbines pressure waves propagating upstream the main flow into the compressor system are generated leading to incidence variations. Numerical and experimental investigations of stator vanes have shown that Active Flow Control (AFC) by means of adaptive blade geometries is beneficial when such periodic incidence variations occur. A significant risk reduction in a compressor facing disturbances can thereby be achieved concerning stall or choke. Experimental investigations on such an AFC method with simultaneous application of a closed-loop control are missing in order to demonstrate its potential. This work investigates a linear compressor cascade that is equipped with a 3D-manufactured piezo adaptive blade structure. The utilized actuators are piezoelectric Macro-Fiber-Composites. A throttling device is positioned downstream the trailing edge plane to emulate an unsteady combustion process. Periodic transient throttling events with a frequency of up to 20 Hz cause incidence changes to the blade’s leading edge. Consequently, pressure fluctuations on the blade’s surface occur, having a significant impact on the pressure recovery downstream of the stator cascade. Experimental results of harmonically actuating the piezo adaptive blade with the corresponding disturbance frequency show that the impact of disturbances can be reduced to approx. 50 %. However, this is only effective if the phase shift of the harmonic actuation is adjusted correctly. Using an inadequate phase shift reverses the positive effects, causing the aforementioned stall, choke, or significant losses. In order to find the optimum phase shift, even under varying, possibly unpredictable operating conditions, an Extremum Seeking Controller is presented. This gradient-based approach is minimizing the pressure variance over time by carefully adjusting the phase shift of the harmonic actuation of the AFC system.

The Development of Active Flow Control Devices From Shape Memory Alloys for the Convective Cooling of Heated Surfaces

2008 ◽  
Author(s):  
Mohd S. Aris ◽  
Ieuan Owen ◽  
Chris J. Sutcliffe
Keyword(s):  
Heat Transfer ◽  
Flow Control ◽  
Heated Surface ◽  
Active Flow Control ◽  
Control Device ◽  
Flow Control Devices ◽  
Flow Control Device ◽  
Control Devices ◽  
Channel Configuration ◽  
Active Flow

This paper is concerned with the convective heat transfer of heated surfaces through the use of active flow control devices. An investigation has been carried out into the use of two flow control design configurations manufactured from Shape Memory Alloys (SMAs) which are activated at specified temperatures. In this design, a high surface temperature would activate rectangular flaps to change shape and protrude at a 45° angle of attack. This protrusion would generate longitudinal vortices and at the same time allow air to flow into cooling channels underneath the flaps, cooling a heated surface downstream of the flow control device. One- and two-channel flow control configurations were explored in this work. The flow control device was made from pre-alloyed powders of SMA material in a rapid prototyping process known as Selective Laser Melting (SLM). It was tested for its heat transfer enhancement in an open test section wind tunnel supplied with low velocity air flow. Infrared thermography was used to evaluate the surface temperatures of the downstream heated surface. Promising results were obtained for the flow control design when the heated surface temperatures were varied from 20 °C to 85 °C. In the one-channel configuration, the flow control device in its activated shape increased heat transfer to a maximum of 50% compared to its deactivated shape. The activated flow control device in the two-channel configuration experienced a heat transfer enhancement of up to 90% compared to when it is deactivated.

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