“…For all the cases of β, the maximum of urms is bound to happen between x/c = 0.06 and 0.08, which is also relatively closer to bubble maximum displacement. 36 The values of maximum urms for β=0°, −30°, and +30° are found to be 24.9%, 29.8%, and 36.6% of their respective local free-stream velocity.Figure 11.Comparison of urms profiles among different β . Profiles are extracted along the midplane of the model.…”
Section: Mean Flow Characteristicsmentioning
confidence: 92%
“…Recent work by Dellacasagrande et al 36 on laminar separation bubbles has proposed a correlation for the onset of transition, based on Re, Tu, and β variation…”
The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.
“…For all the cases of β, the maximum of urms is bound to happen between x/c = 0.06 and 0.08, which is also relatively closer to bubble maximum displacement. 36 The values of maximum urms for β=0°, −30°, and +30° are found to be 24.9%, 29.8%, and 36.6% of their respective local free-stream velocity.Figure 11.Comparison of urms profiles among different β . Profiles are extracted along the midplane of the model.…”
Section: Mean Flow Characteristicsmentioning
confidence: 92%
“…Recent work by Dellacasagrande et al 36 on laminar separation bubbles has proposed a correlation for the onset of transition, based on Re, Tu, and β variation…”
The effect of pressure gradient on a separated boundary layer past the leading edge of an airfoil model is studied experimentally using electronically scanned pressure (ESP) and particle image velocimetry (PIV) for a Reynolds number ( Re) of 25,000, based on leading-edge diameter ( D). The features of the boundary layer in the region of separation and its development past the reattachment location are examined for three cases of β (−30°, 0°, and +30°). The bubble parameters such as the onset of separation and transition and the reattachment location are identified from the averaged data obtained from pressure and velocity measurements. Surface pressure measurements obtained from ESP show a surge in wall static pressure for β = −30° (flap deflected up), while it goes down for β = +30° (flap deflected down) compared to the fundamental case, β = 0°. Particle image velocimetry results show that the roll up of the shear layer past the onset of separation is early for β = +30°, owing to higher amplification of background disturbances compared to β = 0° and −30°. Downstream to transition location, the instantaneous field measurements reveal a stretched, disoriented, and at instances bigger vortices for β = +30°, whereas a regular, periodically shed vortices, keeping their identity past the reattachment location, is observed for β = 0° and −30°. Above all, this study presents a new insight on the features of a separation bubble receiving a disturbance from the downstream end of the model, and these results may serve as a bench mark for future studies over an airfoil under similar environment.
“…The LSB can change the effective body shape seen by the flow which may lead to a loss of performance, vibration, and noise generation in the blade. 1 The previous investigations have revealed that the length of the LSB decreases and it moves toward to leading-edge as either Reynolds number or angles of attack are increased. The force measurements performed by Koca et al 2 at low Reynolds number on an NACA4412 airfoil has shown an abrupt stall due to the LSB burst.…”
Effects of dielectric barrier discharge plasma have been studied on the wake velocity profiles of a section of a 660 kW wind turbine blade in plunging motion in a wind tunnel. The corresponding unsteady velocity profiles show remarkable improvement when the plasma actuators were operating and the angles of attack of the model were beyond the static stall angles of the airfoil. As a result the drag force was considerably reduced. It is further observed that the plasma-induced flow attenuates the leading edge vortices that are periodically shed into wake and diminishes the large eddies downstream. The favorable effects of the plasma augmentation are shown to occur near the uppermost and lowermost positions of the plunging paths where the wake is primarily dominated by the vortices of the same sign. The wake structure in the presence of the flow induced by the plasma actuators shows that the actual effective angles of attack seen by the plunging airfoil reduces in comparison with that for the case of the plasma augmentation off situation.
“…The parameters that strongly affect the separation bubble are the free stream conditions including the Reynolds number and the angles of attack, surface roughness and of course, the body shape. 1 It has been found that the length of the LSB decreases and it moves towards to leading-edge as increasing either of the Reynolds number or the angle of attack, though some studies reported a reduction in LSB length for certain airfoils such as LA2573a. 2,3 The force measurements performed by Koca et al 4 at low Reynolds number on a NACA4412 airfoil has shown an abrupt stall due to the LSB burst.…”
An extensive experimental investigation was conducted to study the effects of Dielectric Barrier Discharge (DBD), on the flow field of an airfoil at low Reynolds number. The DBD was mounted near the leading edge of a section of a wind turbine blade. It is believed that DBD can postpone the separation point on the airfoil by injecting momentum to the flow. The effects of steady actuations on the velocity profiles in the wake region have been investigated. The tests were performed at α = 4 to 36 degrees i.e. from low to deep stall angles of attack regions. Both surface pressure distribution and wake profile show remarkable improvement at high angles of attack, beyond the static stall angle of the airfoil when the plasma actuation was implemented. The drag calculated from the wake momentum deficit has further shown the favorable role of the plasma actuators to control the flow over the airfoil at incidences beyond the static stall angle of attack of this airfoil. The results demonstrated that DBD has been able to postpone the stall onset significantly. It has been observed that the best performance for the plasma actuation for this airfoil is in the deep stall angles of attack range. However, below and near the static stall angles of attack, plasma augmentation was pointed out to have a negligible improvement in the aerodynamic behavior.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
