Theory Of Wing Sections Including A Summary Of Airfoil Data

Influence of actuation parameters of multi-DBD plasma actuators on the static and dynamic behaviour of an airfoil in unsteady flow

The effect of wavy leading ledge, in the manner seen in humpback whales, known as tubercles, to the leading edge of a NACA 4415 airfoil is investigated experimentally at low Reynolds number of 120,000. Comparisons are carried out against a baseline NACA-4415 airfoil is addressed through surface flow visualization, surface pressure and particle image velocimetry (2D-PIV) measurements. Experiments were carried out at angles of attack of 6° and 18° corresponding to pre-stall and post-stall conditions of the baseline airfoil with free stream velocity of 7.5 m/s. The oil-flow visualization studies reveal interesting complex flow features, repeating behind every tubercle at both angles of attack. At the lower angle of attack the extent of the laminar separation bubble, which is a dominant feature on the baseline airfoil, is significantly altered by the presence of the tubercles, which result in the formation of smaller separation bubbles spread along the span instead of one single bubble. The 2-D PIV and oil flow results angle of attack of 18° show that tubercles are very much effective beyond the stall conditions of the base line airfoil. They maintain attached flow till 50% of the cord at least in regions behind the tubercles, instead of complete separation at the leading edge as noticed for the baseline case. The size of recirculating zone downstream of the airfoil post-stall is also significantly reduced by the tubercles. All these factors contribute to the increased performance of the tubercles compared to the baseline NACA 4415 airfoil. However, post-stall the use of tubercles seems to impose a highly varying separation point and subsequently the associated wake width on the airfoil, the effects of which are yet to be explored in detail.

Experimental Studies on the Effect of Leading-Edge Tubercles on Laminar Separation Bubble

The proposed passive control method, blade-end slots, is implemented to reorganize the blade-end flow in a highly loaded compressor cascade under a wide incidence range at Ma=0.59. Both experimenta...

Passive Separation Control with Blade-End Slots in a Highly Loaded Compressor Cascade

Assessment methods for unsteady flow distortion in aero-engine intakes

Tubercles are modifications to the leading edge of an airfoil in the form of blunt wave-like serrations. Several studies on the effect of tubercles on isolated airfoils have shown a beneficial effect in the poststall regime as reduced drag and increased lift, leading to a delay of stall. The prospect of delaying stall is particularly attractive to designers of axial compressors in gas turbines, because this leads to designs with higher loading and therefore higher pressure rise with fewer number of stages. In the present study, experiments were performed on a cascade of airfoils with a NACA 65209 profile with different tubercle geometries. The measurements were made over an exit plane using a five-hole probe to compare the cascade performance parameters. Additionally, hot-wire measurements were taken near the blade surface to understand the nature of the flow in the region close to the tubercles. Oil-flow visualization on the cascade end wall reveals the flow through the passage of blades with and without...

Effect of Leading-Edge Tubercles on Compressor Cascade Performance

Effectiveness of vortex generator jets and wall suction on separated flows in serpentine-duct diffuser

Turbomachinery aeroelasticity is gaining renewed interest in the light of current trends, which tend toward thinner blade designs that are not only highly loaded, but also have minimal weight. This...

Aerodynamic Influence of Oscillating Adjacent Airfoils in a Linear Compressor Cascade

In the present study, the effectiveness of passive structures called tubercles on an axial compressor blade row is studied experimentally. Tubercles are the modifications to the leading edge of an airfoil in the form of blunt wave-like serrations. Although several studies on the effect of tubercles on isolated blades are available in literature, detailed study of their effect on a cascade of blades, such as in the case of an axial flow turbo-machine is lacking. Such an application in an axial compressor will result in a significant increase in the stall margin. Presently, experiments have been performed on a linear compressor cascade with a blade height of 0.15 m and mean chord of 0.06 m, on a NACA 65209 airfoil profile. The plain and modified blades are fabricated using rapid prototyping to ensure conformity to the required geometry. The cascade is designed in such a way that the incidence (angle of attack) and the stagger can be changed easily. The measurements are taken at the exit plane using a five-hole Pitot probe to obtain three-components of velocity and static pressure data over fine measurement grids. The effect is determined in terms of lift and drag coefficients, lift-to-drag ratio and total pressure loss coefficient. Experiments have been carried out for different pitch and amplitude (serration depth) of tubercles to understand their effect. The stall incidence angle for the best performing blade is found to increase up to 8.6° from that of the unmodified blade of 6.0°. Application of such structures in axial compressor blades may well be adequate to prevent stalling in axial compressors over a wide operating range.© 2014 ASME

Experimental Investigation of Effects of Leading-Edge Tubercles on Compressor Cascade Performance

This study addresses flutter that can occur in compressors when operating at high relative incidence. Studies are performed on a subsonic annular compressor cascade containing a sector of blades that can be subjected to controlled torsional oscillation. Measurements taken on the centrally located blade are used to study the unsteady surface pressures developed. Three large mean incidences are considered to characterize the aeroelastic performance. Aerodynamic damping is calculated for each test condition and its variation due to interblade phase angle (IBPA), reduced frequency, and incidence is studied. The source of stability or instability is traced to the nature of unsteady pressures. When the incidence is below the static-stall limit, an increasing incidence is found to exhibit aeroelastically more stable performance, whereas beyond the limit, the stability worsens. For the latter, the amount of improvement in stability by increasing reduced frequency is less compared to the former and its variation with IBPA is not as regular owing to the associated large uncertainty. The nonlinearity effects were found to be relatively higher for this case, especially from the aft region of the suction surface. It is also found that the phase of the local fluctuating pressure and its location on the chord has a decisive influence on the aerodynamic damping and its trends with respect to various parameters are discussed. The results are expected to be useful in the assessing aerodynamic damping trends in relation to the pressure phase variations in specific regions along the chord.

M. C. Keerthi

Papers

Effect of Leading-Edge Tubercles on Compressor Cascade Performance

Effectiveness of vortex generator jets and wall suction on separated flows in serpentine-duct diffuser

Aerodynamic Influence of Oscillating Adjacent Airfoils in a Linear Compressor Cascade

Experimental Investigation of Effects of Leading-Edge Tubercles on Compressor Cascade Performance

Experimental study of aerodynamic damping of an annular compressor cascade with large mean incidences