An Experimental Investigation of the 30P30N Multi-Element High-Lift Airfoil

Abstract

High-lift devices often generate an unsteady flow field producing both broadband and tonal noise which radiates from the aircraft. In particular, the leading edge slat is often a dominant contributor to the noise signature. An experimental study of a simplified unswept high-lift configuration, the 30P30N, has been conducted to understand and identify the various flow-induced noise sources around the slat. Closed-wall wind tunnel tests are performed in the Florida State Aeroacoustic Tunnel (FSAT) to characterize the slat cove flow field using a combination of surface and off-body measurements. Mean surface pressures compare well with numerical predictions for the free-air configuration. Consistent with previous measurements and computations for 2D high-lift configurations, the frequency spectra of unsteady surface pressures on the slat surface display several narrowband peaks that decrease in strength as the angle of attack is increased. At positive angles of attack, there are four prominent peaks. The three higher frequency peaks correspond, approximately, to a harmonic sequence related to a feedback resonance involving unstable disturbances in the slat cove shear layer. The Strouhal numbers associated with these three peaks are nearly insensitive to the range of flow speeds (41-58 m/s) and the angles of attack tested (3-8.5 • ). The first narrow-band peak has an order of magnitude lower frequency than the remaining peaks and displays noticeable sensitivity to the angle of attack. Stereoscopic particle image velocimetry (SPIV) measurements provide supplementary information about the shear layer characteristics and turbulence statistics that may be used for validating numerical simulations. Nomenclature bAirfoil span [m] c Airfoil stowed chord [m] C p Coefficient of pressure f Frequency [Hz] G Autospectral density function [Pa 2 /Hz] L γ Coherence length [m] m, n Transducer indicies N Total number of transducers P SD Power spectral density [Pa 2 /Hz] q Dynamic freestream pressure [Pa] Re c Reynolds number based on c s Slat chord [m] St s Strouhal number based on s T KE Turbulent kinetic energy U ∞ Freestream velocity [m/s] |V | Velocity vector magnitude [m/s] u, v, w Velocity components [m/s] x Chordwise distance [m] ∆z Spanwise distance [m] α Geometric angle of attack [ • ] γ 2 Ordinary coherence function ω z Spanwise vorticity [1/s] · Ensemble average of quantity Superscript: () * Nondimensional units () ′ Fluctuating quantity

Experiments on Slat Noise from -6° to 18° Angles of Attack

“…Figures 7 and 10, show noise spectra for such lower angles of attack are broadband-like and their noise intensity levels are closer to those of the wind-tunnel. The slat noise components of multiple tonal peaks of low-frequency and high-frequency broad tone,, 17,10,38,10,18,39,23,13,40,5,6,41,42,9,8,19 emerges after an increase in the angle of attack, i. e., after −2 • . For higher angles of attack, i. e., above 10 • , the multiple tonal peaks component is suppressed and the broadband component emerges, but in a lower intensity than that of lower angles of attack employed.…”

“…Slat noise has been studied from wind tunnel measurements 5,6,7,8,9 , numerical simulations 10,11,12,13,14,15 , and flyover tests 16 . Wind tunnel experiments using scaled high-lift models have revealed a slat noise signature featuring from broadband to tonal noise components.…”

Assessment of Slat Noise Predictions for 30P30N High-Lift Configuration from BANC-III Workshop

“…The 2-D geometry of the 30P30N configuration is simple enough to allow a broad set of flow solvers to be applied, which is confirmed by the previous observation that this configuration has been embraced in a variety of workshops with rather different objectives. 18,26,37 The low Reynolds number in Category 7 of the BANC-III workshop also implies that boundary layer transition over the slat should not be a major influence on the overall computation because the flow over the majority of the slat is laminar at this Re. Separation points on the slat are fixed by the model geometry; however, the reattachment location is jointly determined by the overall surface pressure distribution and the accuracy in predicting the evolution of unsteady flow structures along the shear layer that bounds the separated flow region within the slat cove.…”

“…17 Category 7 of the BANC series of workshops targets the slat cove noise associated with the generic, zero sweep, 30P30N high-lift configuration. 18 For the BANC-III Workshop, a total of twelve teams performed computational predictions of various aerodynamic and aeroacoustic metrics ranging from mean and unsteady force coefficients, surface pressure distributions including power spectral density (PSD) and spanwise coherence, off-body velocity field in regions of attached and separated flow, and acoustic spectra representative of flyover measurements. Three other teams contributed complementary information derived from previously conducted simulations for the same geometry and either the same or related flow conditions.…”

Numerical Determination of Critical Mach Number of a Three -Element Airfoil in Unbounded Flow and in Ground Effect

“…The typical geometry of a high-lift airfoil from leading edge to trailing edge consists of three parts: slat, main and flap. As shown in The 30P30N is a well-studied high-lift airfoil; geometric settings such as the gap and overhang of the slat and the flap are summarized in Table 2.1 [8].…”