Proceedings Of The Institution Of Mechanical Engineers, Part G: Journal Of Aerospace Engineering, Jul 11, 2022
The harmonic vortex shedding from airfoil happens in various incidences. It has noticeable effect... more The harmonic vortex shedding from airfoil happens in various incidences. It has noticeable effects on the structure design and aerodynamic performance. In this paper, wind tunnel tests were conducted on a stationary NACA4412 airfoil at angles of attack ranging from [Formula: see text] to [Formula: see text] and Re number between [Formula: see text] and [Formula: see text] to examine the vortex shedding frequency and Strouhal number. The wake dynamics at post-stall incidences were investigated by surface pressure, wake flow velocity measurement, and smoke flow visualization. Three phases of the wake dynamics were observed with increasing the incidences beyond the stall: (i) the tiny vortices are shed from the airfoil’s suction side with scattered frequencies, (ii) the shear layer is separated from the LE, rolls up over the airfoil’s suction side and forms the harmonic vortex street, and (iii) the separation point moves from the airfoil’s suction side to the pressure side and leads to the vortex shedding like the bluff bodies. Frequency analysis of aerodynamic loads shows that the flow field’s low-frequency feature has a substantial effect normal to the surface while the vortex street unsteadiness impacts both perpendicular and parallel to the surface. The base pressure coefficient increases suddenly by the vortex street onset in the region (ii) and reaches about 0.4. The universal Strouhal number of 0.18 that is independent of Reynolds number was captured for the angles of attack well beyond the stall. Flow visualization shows that the vortex street establishes longitudinally closer to the airfoil at lower freestream velocity compared to the upper one.
Transactions of The Canadian Society for Mechanical Engineering, Jun 1, 2015
In the current research, the results of a number of wind-tunnel experiments on a moving airfoil w... more In the current research, the results of a number of wind-tunnel experiments on a moving airfoil with plunging motion are presented. The experiments have been conducted in two different configurations which are tunnels with conventional and slotted test-section walls to provide resemblance to a far-field condition. The difference in results obtained from two test-section configurations can be considered as the wall effect and regulated as a function of non-dimensional parameters which can be further used for correcting experimental results obtained from conventional wind tunnels. When the derived correction factor is applied to a numerical simulation of a wind tunnel with a conventional test section (for points located in the front portion of the airfoil), the resulting pressure variations closely resembled that of a far-field numerical simulation. This methodology showed promising results for the specific configurations used in this research.
In this experimental investigation, a pulse flow control system on a high-lift device of a wing w... more In this experimental investigation, a pulse flow control system on a high-lift device of a wing with a NASA SC(2)-0714 airfoil within the Reynolds number range of the take-off and landing phases, is proposed. In this study, an innovative method of signal modulation has been used in order to simultaneously exploit the benefits of both low and high excitation frequencies in one actuator driving signal that are known to be effective in separation control. It is observed that the lift and drag coefficients are improved due to the use of modulated pulse jets compared to the simple pulse jet.
The feasibility of a single dielectric barrier discharge (SDBD) actuator in controlling flow over... more The feasibility of a single dielectric barrier discharge (SDBD) actuator in controlling flow over an Ahmed body, representing a simplified car model, has been numerically and experimentally investigated at Reynolds numbers of 7.68×105 and 2.25×105. The Ahmed body had slant angles of 25∘ and 35∘. The results showed that SDBD actuators could significantly enhance the aerodynamic performance of the Ahmed body. Several arrangements of the actuators on the slant surface and the rear face of the model were examined to identify the most effective arrangement for drag reduction. This arrangement resulted in an approximately 6.1% drag reduction. This improvement in aerodynamic performance is attributed to the alteration of three-dimensional wake structures due to the presence of SDBD, which coincides with surface pressure variations on the slant and rear faces of the Ahmed body.
The unsteady wake of an EPPLER 361 airfoil in pitching motion has been investigated in a subsonic... more The unsteady wake of an EPPLER 361 airfoil in pitching motion has been investigated in a subsonic wind tunnel by hot-wire anemometry. The airfoil was given the pitching motion about the one-quarter chord axis at reduced frequency of 0182. Streamwise mean velocity profiles (wake profiles) were investigated at several vertically aligned points behind the airfoil at one-quarter chord downstream distance from trailing edge. Oscillation amplitude and mean angle of attack were varied to determine the effects on wake profiles. When the maximum dynamic angle of attack was below the static stall angle of attack, weak effects on wake were found by increasing oscillation amplitude and mean angle of attack. But, for higher angles of attack strong unsteady effects were appeared on the wake.
An experimental measurements of unsteady wakes behind a sinusoidally plunging airfoil was surveye... more An experimental measurements of unsteady wakes behind a sinusoidally plunging airfoil was surveyed with a Hot-wire rake containing seven I-wires. The aim of these measurements was to study the velocity profiles behind the oscillating airfoil trailing edge. Influences of reduced frequency and angle of attack were studied in details. It was shown that the angle of attack and reduced frequency are the most important parameters which influence on the velocity profiles. The momentum deficit was relative to reduced frequency and amplitude of oscillation and its behaviours were changed after static stall angles. At the angle of attack beyond static stall angle flow separation causes increasing the momentum deficit. The velocity profile has approximately symmetric shape profile. Data were taken at mean incidence angles of 0, 8 degrees at reduced frequencies of 0.09 to 0.56. The nondimensional amplitude of oscillation was 0.27. The corresponding Reynolds numbers, based on the chord length, w...
In the current research, the results of some wind tunnel experiments on a moving airfoil with plu... more In the current research, the results of some wind tunnel experiments on a moving airfoil with plunging motion are presented. The experiments have been conducted in two different configurations which are tunnels with conventional and slotted walls. In both cases, pressure coefficients of different points on the upper surface of the airfoil have been measured during the plunging oscillation. The difference between the outputs is considered as the wall effect. The mentioned difference is extracted and regulated as a function of some non-dimensional parameters to provide a data-base for correction of the results of experiments on oscillating airfoils conducted in conventional wind tunnels. The correction is only considered for points located in the front portion of the airfoil to make sure there is no flow separation in that region. Finally, numerical experiments are employed to show the performance of the method.
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2020
In the current research, a series of different combinations of plasma SDBD actuators mounted on a... more In the current research, a series of different combinations of plasma SDBD actuators mounted on a simplified road vehicle have been experimentally studied to find the optimum position of the actuators for controlling the flow separation and reducing the vehicle form drag. Separation point of the flow over the rear ramp, large trailing vortices of the standard model, and laminar separation bubble (LSB) of the rear ramp leading edge are among the most significant factors to be controlled. The experiments were conducted at Reynolds numbers ranging from 0.55 × 106 to 1.11 × 106 in a subsonic wind tunnel while the pressure distribution over the model and its streamwise force balance were accurately measured. Significant drag reduction due to the use of DBD actuators was observed. As such, for the range of tested Reynolds numbers, a maximum of 25.1% of drag reduction in the vehicle drag coefficient could be achieved. The optimum combinations of activation voltages (6, 9, and 12 kV) and wa...
Transactions of the Canadian Society for Mechanical Engineering, 2015
In the current research, the results of a number of wind-tunnel experiments on a moving airfoil w... more In the current research, the results of a number of wind-tunnel experiments on a moving airfoil with plunging motion are presented. The experiments have been conducted in two different configurations which are tunnels with conventional and slotted test-section walls to provide resemblance to a far-field condition. The difference in results obtained from two test-section configurations can be considered as the wall effect and regulated as a function of non-dimensional parameters which can be further used for correcting experimental results obtained from conventional wind tunnels. When the derived correction factor is applied to a numerical simulation of a wind tunnel with a conventional test section (for points located in the front portion of the airfoil), the resulting pressure variations closely resembled that of a far-field numerical simulation. This methodology showed promising results for the specific configurations used in this research.
Proceedings Of The Institution Of Mechanical Engineers, Part G: Journal Of Aerospace Engineering, Jul 11, 2022
The harmonic vortex shedding from airfoil happens in various incidences. It has noticeable effect... more The harmonic vortex shedding from airfoil happens in various incidences. It has noticeable effects on the structure design and aerodynamic performance. In this paper, wind tunnel tests were conducted on a stationary NACA4412 airfoil at angles of attack ranging from [Formula: see text] to [Formula: see text] and Re number between [Formula: see text] and [Formula: see text] to examine the vortex shedding frequency and Strouhal number. The wake dynamics at post-stall incidences were investigated by surface pressure, wake flow velocity measurement, and smoke flow visualization. Three phases of the wake dynamics were observed with increasing the incidences beyond the stall: (i) the tiny vortices are shed from the airfoil’s suction side with scattered frequencies, (ii) the shear layer is separated from the LE, rolls up over the airfoil’s suction side and forms the harmonic vortex street, and (iii) the separation point moves from the airfoil’s suction side to the pressure side and leads to the vortex shedding like the bluff bodies. Frequency analysis of aerodynamic loads shows that the flow field’s low-frequency feature has a substantial effect normal to the surface while the vortex street unsteadiness impacts both perpendicular and parallel to the surface. The base pressure coefficient increases suddenly by the vortex street onset in the region (ii) and reaches about 0.4. The universal Strouhal number of 0.18 that is independent of Reynolds number was captured for the angles of attack well beyond the stall. Flow visualization shows that the vortex street establishes longitudinally closer to the airfoil at lower freestream velocity compared to the upper one.
Transactions of The Canadian Society for Mechanical Engineering, Jun 1, 2015
In the current research, the results of a number of wind-tunnel experiments on a moving airfoil w... more In the current research, the results of a number of wind-tunnel experiments on a moving airfoil with plunging motion are presented. The experiments have been conducted in two different configurations which are tunnels with conventional and slotted test-section walls to provide resemblance to a far-field condition. The difference in results obtained from two test-section configurations can be considered as the wall effect and regulated as a function of non-dimensional parameters which can be further used for correcting experimental results obtained from conventional wind tunnels. When the derived correction factor is applied to a numerical simulation of a wind tunnel with a conventional test section (for points located in the front portion of the airfoil), the resulting pressure variations closely resembled that of a far-field numerical simulation. This methodology showed promising results for the specific configurations used in this research.
In this experimental investigation, a pulse flow control system on a high-lift device of a wing w... more In this experimental investigation, a pulse flow control system on a high-lift device of a wing with a NASA SC(2)-0714 airfoil within the Reynolds number range of the take-off and landing phases, is proposed. In this study, an innovative method of signal modulation has been used in order to simultaneously exploit the benefits of both low and high excitation frequencies in one actuator driving signal that are known to be effective in separation control. It is observed that the lift and drag coefficients are improved due to the use of modulated pulse jets compared to the simple pulse jet.
The feasibility of a single dielectric barrier discharge (SDBD) actuator in controlling flow over... more The feasibility of a single dielectric barrier discharge (SDBD) actuator in controlling flow over an Ahmed body, representing a simplified car model, has been numerically and experimentally investigated at Reynolds numbers of 7.68×105 and 2.25×105. The Ahmed body had slant angles of 25∘ and 35∘. The results showed that SDBD actuators could significantly enhance the aerodynamic performance of the Ahmed body. Several arrangements of the actuators on the slant surface and the rear face of the model were examined to identify the most effective arrangement for drag reduction. This arrangement resulted in an approximately 6.1% drag reduction. This improvement in aerodynamic performance is attributed to the alteration of three-dimensional wake structures due to the presence of SDBD, which coincides with surface pressure variations on the slant and rear faces of the Ahmed body.
The unsteady wake of an EPPLER 361 airfoil in pitching motion has been investigated in a subsonic... more The unsteady wake of an EPPLER 361 airfoil in pitching motion has been investigated in a subsonic wind tunnel by hot-wire anemometry. The airfoil was given the pitching motion about the one-quarter chord axis at reduced frequency of 0182. Streamwise mean velocity profiles (wake profiles) were investigated at several vertically aligned points behind the airfoil at one-quarter chord downstream distance from trailing edge. Oscillation amplitude and mean angle of attack were varied to determine the effects on wake profiles. When the maximum dynamic angle of attack was below the static stall angle of attack, weak effects on wake were found by increasing oscillation amplitude and mean angle of attack. But, for higher angles of attack strong unsteady effects were appeared on the wake.
An experimental measurements of unsteady wakes behind a sinusoidally plunging airfoil was surveye... more An experimental measurements of unsteady wakes behind a sinusoidally plunging airfoil was surveyed with a Hot-wire rake containing seven I-wires. The aim of these measurements was to study the velocity profiles behind the oscillating airfoil trailing edge. Influences of reduced frequency and angle of attack were studied in details. It was shown that the angle of attack and reduced frequency are the most important parameters which influence on the velocity profiles. The momentum deficit was relative to reduced frequency and amplitude of oscillation and its behaviours were changed after static stall angles. At the angle of attack beyond static stall angle flow separation causes increasing the momentum deficit. The velocity profile has approximately symmetric shape profile. Data were taken at mean incidence angles of 0, 8 degrees at reduced frequencies of 0.09 to 0.56. The nondimensional amplitude of oscillation was 0.27. The corresponding Reynolds numbers, based on the chord length, w...
In the current research, the results of some wind tunnel experiments on a moving airfoil with plu... more In the current research, the results of some wind tunnel experiments on a moving airfoil with plunging motion are presented. The experiments have been conducted in two different configurations which are tunnels with conventional and slotted walls. In both cases, pressure coefficients of different points on the upper surface of the airfoil have been measured during the plunging oscillation. The difference between the outputs is considered as the wall effect. The mentioned difference is extracted and regulated as a function of some non-dimensional parameters to provide a data-base for correction of the results of experiments on oscillating airfoils conducted in conventional wind tunnels. The correction is only considered for points located in the front portion of the airfoil to make sure there is no flow separation in that region. Finally, numerical experiments are employed to show the performance of the method.
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2020
In the current research, a series of different combinations of plasma SDBD actuators mounted on a... more In the current research, a series of different combinations of plasma SDBD actuators mounted on a simplified road vehicle have been experimentally studied to find the optimum position of the actuators for controlling the flow separation and reducing the vehicle form drag. Separation point of the flow over the rear ramp, large trailing vortices of the standard model, and laminar separation bubble (LSB) of the rear ramp leading edge are among the most significant factors to be controlled. The experiments were conducted at Reynolds numbers ranging from 0.55 × 106 to 1.11 × 106 in a subsonic wind tunnel while the pressure distribution over the model and its streamwise force balance were accurately measured. Significant drag reduction due to the use of DBD actuators was observed. As such, for the range of tested Reynolds numbers, a maximum of 25.1% of drag reduction in the vehicle drag coefficient could be achieved. The optimum combinations of activation voltages (6, 9, and 12 kV) and wa...
Transactions of the Canadian Society for Mechanical Engineering, 2015
In the current research, the results of a number of wind-tunnel experiments on a moving airfoil w... more In the current research, the results of a number of wind-tunnel experiments on a moving airfoil with plunging motion are presented. The experiments have been conducted in two different configurations which are tunnels with conventional and slotted test-section walls to provide resemblance to a far-field condition. The difference in results obtained from two test-section configurations can be considered as the wall effect and regulated as a function of non-dimensional parameters which can be further used for correcting experimental results obtained from conventional wind tunnels. When the derived correction factor is applied to a numerical simulation of a wind tunnel with a conventional test section (for points located in the front portion of the airfoil), the resulting pressure variations closely resembled that of a far-field numerical simulation. This methodology showed promising results for the specific configurations used in this research.
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