Time-resolved wake measurements of separated wing flow

Transcription

1 ESWIRP Workshop Time-resolved wake measurements of separated wing flow , Th. Lutz, E. Krämer, Ph. Gansel /luftfahrzeugaerodynamik

2 Outline Motivation Existing time-resolved particle image velocimetry (TR-PIV) measurements Proposed ESWIRP tests PIV test requirements

3 Motivation Stalling of transport aircraft produces massively separated flow in the wake of the wing. Unsteady oscillating of the separation point and large scale turbulent fluctuations lead to strong unsteadiness of the wake flow upstream of the horizontal tail plane (htp). High speed stall of a wing-body-conf. (zonal DES) [1] Low speed airfoil stall (current IAG DES) [1]: Brunet, V., Deck, S.: Zonal-Detached Eddy Simulation of Transonic Buffet on a Civil Aircraft Type Configuration, AIAA

4 Motivation Example of measured unsteady pressure fluctuations at htp (low speed wind tunnel; Havas et al., 2009) [2] separated main wing flow (stall) attached main wing flow stall attached negative htp setting angle positive htp setting angle [2]: Havas, J., Rabadan, G.J.: Prediction of Horizontal Tail Plane Buffeting Loads, IFASD

5 Motivation Possible negative effects on the empennage: Excitation of structural responses due to unsteady air loads in a eigenmode relevant frequency domain. Influence on the efficiency of control surfaces (horizontal stabilizer and elevator). Induced and excited unsteady rolling moment at htp due to asymmetry in the wake of the main wing flow separation. The effects of flow unsteadiness at the tail plane can be safety critical.

6 Motivation Time- and space-resolved flow field studies are required to: analyse the development and propagation of turbulent wake structures. predict their impact on htp flow and overall aircraft characteristics in a stall flight regime. find correlations between unsteady separated wing flow and the impact on the empennage (loads, load fluctuations, load alleviation). validate numerical simulations with resolved turbulent fluctuations in the wing wake (DES).

7 Existing TR-PIV measurements 1. Low Re TR-PIV in the vicinity of a NACA0015 with Gurney flap [3] Test case: NACA0015 Re = α = 0 20 Instantaneous velocity fields TR-PIV measurements: 5 khz sampling rate 1024 x 1024 pixels resolution (141 mm) 2 field vector distance 2,2 mm Power spectral density (PSD) in comparison to hot wire anemometry [3]: Troolin, D. R., Longmire, E. K., Lai, W. T.: Time resolved PIV analysis of flow over a NACA 0015 airfoil with Gurney flap, Experiments in Fluids 41, , 2006.

8 Existing TR-PIV measurements 2. Low Re TR-PIV near the trailing edge of an airfoil with plasma actuator [4] Test case: NACA0012 airfoil Re = α = -2,5 Roughness tapes for vortex generation TR-PIV measurements: 5 khz sampling rate 1024 x 512 pixels resolution 82 mm x 41 mm field vector distance 2,7 mm Velocity fluctuations (u RMS /u ) Space correlation [4]: Koike, S. et al.: Time-Resolved PIV Applied to Trailing-Edge-Noise Reduction by DBD Plasma Actuator, AIAA , 27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, Chicago, Illinois, (2010).

9 Proposed testing in ESWIRP Need for new wind tunnel tests: Time-resolved numerical simulations become feasible, but need to be validated. Available corresponding measurements are restricted to low Re and Ma numbers and the vicinity of the trailing edge. Objectives: Measurement in wing stall and post-stall α-range. Time- and space-resolved wake measurements from wing to tail. Measurements of unsteady pressure loads on the htp. Test case: Full aircraft configuration with public domain geometry. Clean configuration with and without htp. Realistic flight Reynolds number and at least 2 Mach numbers (low speed stall and high speed stall with buffet). Two different Re to study Reynolds number effects

10 Proposed testing in ESWIRP Desired measurement data: TR-PIV recording in several planes parallel and perpendicular to the freestream direction upstream of the htp to acquire unsteady velocity field data. Unsteady wall pressure at discrete locations (Kulites) at the main wing tailing edge and on the htp. Tail loads (balance if possible) for surveying htp and elevator efficiency.

11 PIV test requirements Example values are calculated based on ETW data. Spatial resolution: Wing span of typical model b 1,5 m Reference chord length c 0,185 m Turbulent length scale of modelled turbulence in URANS calculation (NACA0012, c = 0,165 m, Re = , Ma = 0,3, α = 16 ): L 11 (k T, ω) = 0,4% c = 0,75 mm Camera resolution 1600 x 1200 pixels Interrogation area 16 x 16 pixels with 50% overlap Required vector distance L 11 = 0,75 mm measurement field of 75 mm x 56,25 mm

12 PIV test requirements Temporal resolution: Measured peak frequency on aircraft htp in wind tunnel stall tests (scale 1/26, Re = 7, , Ma = 0,2, T = 295,5 K, α = 16 ): f aircraft 4 Hz (corresponding Strouhal number Sr aircraft = 0,0273) Vortex shedding frequency (c l -oscillations) from URANS calculation (NACA0012, c = 0,165 m, Re = , Ma = 0,3, α = 16 ): f URANS = 39,49 Hz (corresponding Strouhal number Sr URANS = 0,0760) Assumed PSD peak frequency in ETW tests: f ETW,peak { Sr aircraft, Sr URANS } * u ETW / c = { 8,8 Hz, 24,6 Hz } Required TR-PIV sampling rate is 2 10 * f ETW,peak to capture spectra characteristics (large scale range, inertial range).