Reduction of Procoagulant Potential of b-Datum Leakage Jet Flow in Bileaflet Mechanical Heart Valves via Application of Vortex Generator Arrays

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
David W. Murphy ◽  
Lakshmi P. Dasi ◽  
Jelena Vukasinovic ◽  
Ari Glezer ◽  
Ajit P. Yoganathan
Keyword(s):  
Flow Control ◽  
Heart Valves ◽  
Thrombus Formation ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Mechanical Heart Valves ◽  
Shear Stresses ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Increased Risk

Current designs of bileaflet mechanical heart valves put patients at an increased risk of thromboembolism. In particular, regurgitant flow through the b-datum line is associated with nonphysiologic flow characteristics such as elevated shear stresses, regions of recirculation, and increased mixing, all of which may promote thrombus formation. We have previously shown that passive flow control in the form of vortex generators mounted on the downstream leaflet surfaces can effectively diminish turbulent stresses. The objective of the current work is thus to determine the effect of vortex generators on the thromboembolic potential of the b-datum line leakage jet and to correlate that effect with the vortex generator-induced changes to the flow structure. Flow experiments were performed using a steady model of the transient b-datum line jet. These experiments encompassed flow visualization to gain an overall picture of the flow system, particle image velocimetry to quantify the flow field in detail, and in vitro experiments with human blood to quantify thrombus formation in response to the applied passive flow control. Thrombus formation was quantified over time by an assay for thrombin-antithrombin III (TAT III). In comparing results with and without vortex generators, significantly lower mean TAT III levels were observed at one time point for the case with vortex generators. Also, the TAT III growth rate of the case with vortex generators was significantly lower. While no differences in jet spreading were found with and without vortex generators, lower peak turbulent stresses were observed for the case with vortex generators. The results thus demonstrate the potential of applying passive flow control to cardiovascular hardware in order to mitigate the hemodynamic factors leading to thrombus formation.

Reduction of Flow-Induced Blood Damage in Bileaflet Mechanical Heart Valves Through Passive Flow Control

2008 ◽  
Author(s):  
David W. Murphy ◽  
Lakshmi P. Dasi ◽  
Ari Glezer ◽  
Ajit P. Yoganathan
Keyword(s):  
Shear Stress ◽  
Platelet Activation ◽  
Heart Valves ◽  
Vortex Generators ◽  
Mechanical Heart Valves ◽  
Shear Stresses ◽  
Valve Closure ◽  
Passive Flow Control ◽  
Blood Damage ◽  
Passive Flow

Bileaflet mechanical heart valves (BMHVs), though a life-saving device in treating heart valve disease, are often associated with several complications including a high risk of hemolysis, platelet activation, and thromboembolism. To address this risk, patients must undergo prophylactic anticoagulation therapy. One likely cause of this hyper-coagulative state is the nonphysiologic levels of stress experienced by the erythrocytes and platelets flowing through the BMHVs. Research has shown that the combination of shear stress magnitude and exposure time found in the highly transient leakage jet emanating from the b-datum gap during valve closure is sufficient to cause hemolysis and platelet activation [1–3]. Reducing the shear stresses experienced by the blood flowing through the b-datum gap during valve closure may therefore reduce the prevalence of valve-related blood damage. Such shear stress reduction could be achieved by passive flow control, in particular vortex generators, incorporated onto the BMHV leaflet surface. Vortex generators have been used to control shear flows in various aerodynamic applications, and it is thus thought that their application to mechanical heart valve leaflet surfaces may reduce shear stresses by creating streamwise vortices that will serve to dissipate the regurgitant jet originating from the b-datum gap at the time of valve closure.

scholarly journals Passive flow control of shock-induced dynamic stall via surface-based trapped vortex generators

2021 ◽  
pp. 095441002110112
Author(s):  
Khider Al-Jaburi ◽  
Daniel Feszty
Keyword(s):  
Flow Control ◽  
Vortex Generator ◽  
Flight Test ◽  
Dynamic Stall ◽  
Test Case ◽  
Negative Effects ◽  
Passive Flow Control ◽  
Passive Flow ◽  
Dynamics Simulations ◽  
Trapped Vortex

A novel passive approach for controlling the flow in a 2D dynamic stall at variabl freestream is investigated. 2D computational fluid dynamics simulations of an SC1095 airfoil with surface-based trapped vortex generator (STVG) type passive flow control were conducted. The airfoil was exposed to a fluctuating freestream of Mach 0.537 ± 0.205 and Re = 6.1 × 106 (based on the mean Mach number) and experienced a 10° ± 10° pitch oscillation with a frequency of 4.25 Hz. These conditions were selected as an approximation to the flow experienced by a UH-60A helicopter rotor airfoil section in an actual fast forward flight test case. The baseline simulations were cautiously validated with experimental data for both transonic flow and dynamic stall under the variable freestream. Then, 20 different local STVGs type geometry modifications were investigated as a means of passive flow control. Modifications were examined on both the airfoil’s upper and lower surfaces. Results showed that the STVGs were able to mitigate the negative effects of shock-induced dynamic stall. The best geometries could reduce the peak negative pitching moment by as much as 9–23% during the transonic phase of a cycle and by as much as 19–71% during the dynamic stall phase. Also, they were able to reduce peak drag by 8–20% in the transonic phase and by 15–44% in the dynamic stall phase. On the other hand, the lift-to-drag ratio was significantly increased by 3–28% per one rotor cycle. All the above advantages came at virtually no penalty in the lift.

Potential of Retrofit Passive Flow Control for Small Horizontal Axis Wind Turbines

2016 ◽  
Author(s):  
D. Holst ◽  
G. Pechlivanoglou ◽  
F. Wegner ◽  
C. N. Nayeri ◽  
C. O. Paschereit
Keyword(s):  
Flow Control ◽  
Wind Turbines ◽  
High Performance ◽  
Horizontal Axis ◽  
Vortex Generators ◽  
Passive Flow Control ◽  
Wind Speeds ◽  
Passive Flow ◽  
Horizontal Axis Wind Turbines ◽  
Low Reynolds

The present paper analyzes the effect of passive flow control (PFC) with respect to the retrofitting on small horizontal axis wind turbines (sHAWT). We conducted extensive wind tunnel studies on an high performance low Reynolds airfoil using different PFC elements, i.e. vortex generators (VGs) and Gurney flaps. QBlade, an open source Blade Element Momentum (BEM) code, is used to study the retrofitting potential of a simulated small wind turbine. The turbine design is presented and discussed. The simulations include the data and polars gained from the experiments and give further insight into the effects of PFC on sHAWT. Therefore several different blades were simulated using several variations of VG positions. This paper discusses their influence on the turbine performance. The authors focus especially on the start-up performance as well as achieving increased power output at lower wind speeds. The vortex generators reduce the risk of laminar separation and enhance the lift in some configurations by more than 40% at low Reynolds numbers.

A Parametric Study of Passive Flow Control for a Short, High Area Ratio 90deg Curved Diffuser

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
T. P. Chong ◽  
P. F. Joseph ◽  
P. O. A. L. Davies
Keyword(s):  
Flow Control ◽  
Area Ratio ◽  
Wire Mesh ◽  
Vortex Generators ◽  
Scale Model ◽  
Experimental Program ◽  
Guide Vanes ◽  
Passive Flow Control ◽  
Passive Flow ◽  
High Area

This paper represents the results of an experimental program with the aim of controlling the flow in a highly unstable 90deg curved diffuser. The diffuser, which is an integral part of an open jet wind tunnel at the University of Southampton, has the unique configuration of extreme shortness and high area ratio. In this study, several passive flow control devices such as vortex generators, woven wire mesh screens, honeycomb, and guide vanes were employed to control the three-dimensional diffusing flow in a scaled-down model. Although less successful for vortex generators, the other devices were found to improve significantly the uniformity of the flow distribution inside the curved diffuser and hence the exit flow. This study suggests that a cumulative pressure drop coefficient of at least 4.5 at the diffuser exit with at least three guide vanes is required to achieve adequate flow uniformity at the diffuser exit. These flow conditioning treatments were applied to the full-scale diffuser with exit dimensions of 1.3×1.3m2. Flow with comparable uniformity to the scale-model diffuser is obtained. This study provides valuable guidelines on the design of curved/straight diffusers with nonseparated flow and minimal pressure distortion at the exit.

Potential of Retrofit Passive Flow Control for Small Horizontal Axis Wind Turbines

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
D. Holst ◽  
G. Pechlivanoglou ◽  
F. Wegner ◽  
C. N. Nayeri ◽  
C. O. Paschereit
Keyword(s):  
Flow Control ◽  
Wind Turbines ◽  
High Performance ◽  
Horizontal Axis ◽  
Vortex Generators ◽  
Passive Flow Control ◽  
Wind Speeds ◽  
Passive Flow ◽  
Horizontal Axis Wind Turbines ◽  
Low Reynolds

The present paper analyzes the effect of passive flow control (PFC) with respect to the retrofitting on small horizontal axis wind turbines (sHAWTs). We conducted extensive wind tunnel studies on a high performance low Reynolds airfoil using different PFC elements, i.e., vortex generators (VGs) and Gurney flaps (GF). qblade, an open source blade element momentum (BEM) code, is used to study the retrofitting potential of a simulated small wind turbine. The turbine design is presented and discussed. The simulations include the data and polars gained from the experiments and give further insight into the effects of PFC on sHAWTs. Therefore, several different blades were simulated using several variations of VG positions. This paper discusses their influence on the turbine performance. The authors especially focus on the startup performance as well as achieving increased power output at lower wind speeds. The vortex generators reduce the risk of laminar separation and enhance the lift in some configurations by more than 40% at low Reynolds numbers.

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