Werner Sachs

Application of Pressure-Sensitive Paint for Determination of Dynamic Surface Pressures on a Rotating 65° Delta Wing and an Oscillating 2D profile in Transonic Flow

Visualization and measurements of aerodynamic effects on a delta-wing model and a 2D-wing-profile model were conducted using an optical pressure measurement system, based on the pressure-sensitive paint (PSP) technique. The PSP technique can be used to obtain absolute pressure measurements on the surface of a model and in addition to evaluate quantitative aerodynamic flow phenomena by using scientific grade cameras and image processing techniques. The PSP technique has been used here for investigations of periodic and unsteady flows: first, a 65deg delta wing was tested in the transonic wind tunnel DNW-TWG in Gottingen. A specially designed roll apparatus enabled roll rates up to 10 Hz. The experiments were carried out at angles-of-attack up to alpha = 17deg at Ma = 0.8. Since the rotation of the delta wing is a periodic motion, the phase-locked unsteady PSP technique can be applied. In a second wind tunnel campaign in the DNW-TWG in collaboration with the DLR Institute of Aeroelasticity, a 2D-wing-profile model, which is pitch oscillating at up to 30 Hz, was investigated. The experiments were performed at angles-of-attack alpha = 1.12deg plusmn 0.6deg at Ma = 0.72. For these experiments pressure measurements were carried out in one wind tunnel entry by means of both phase-locked unsteady as well as unsteady PSP techniques.

Quantitative Wind Tunnel Studies Using Pressure- and Temperature Sensitive Paints

The pressure sensitive paint (PSP) intensity and lifetime system is an optical measurement technique to investigate absolute pressure fields on model surfaces for basic research in laboratories, industrial wind tunnels or high speed rotating turbo machines. Detailed qualitative and quantitative information and understanding of flow phenomena can be obtained in speed ranges from U∞=20 m/s up to Ma=5.0. A number of projects of industrial interest has been investigated in different wind tunnels covering low speed, transonic, trisonic and cryogenic facilities. The influence of the main error sources for the components of the PSP system have been checked. Comparison of experimental pressure fields obtained by means of PSP and the results of numerical calculations have been carried out. Different wind tunnel models ranging from basic configurations such as a cropped delta wing to a complex half model of a large propeller-driven transport aircraft with all flaps, rudders and shrouds, and rotating or oscillating models as well as Reynolds number effects on models have been investigated.

Determination of Transfer Function of Pressure-Sensitive Paint

An experimental setup for detailed and accurate experimental determination of the frequency response of pressure-sensitive paints (PSP) is presented. By use of a mechanical shaker which is connected to a pressure chamber the setup realizes high-quality sinusoidal pressure variations for frequencies ranging from less than 0.1 Hz up to several hundreds of Hz with pressure amplitudes up to ±3 kPa. An appropriate optical system for detection of luminescent light of the PSP has been adapted for the experimental set-up. Unsteady characterization of various formulations of PSP based on the luminophore platinum tetra (pentafluorophenyl)porphine (PtTFPP) in a fluoroacrylic polymer was carried out for frequencies f = 0.1 up to 120 Hz. The influence on frequency response from paint layer thickness was measured. The influence of paint porosity is tested by adding from 0 to 80 mass % TiO2 particles to the PSP. The frequency response is shown to be similar with respect to a characteristic time, which ranged from the order of seconds for no filler to the order of milliseconds for higher amount of TiO2.

Pressure Measurement on Rotating Propeller Blades by means of the Pressure-Sensitive Paint Lifetime Method

The pressure distribution on the surface of a high-speed rotating propeller was measured using the Pressure-Sensitive Paint (PSP) lifetime method. This chapter describes the developed PSP formulation, the experimental setup as well as the image acquisition, processing procedure, and the data evaluation. The PSP lifetime method delivers a continuous pressure distribution, which allows even small pressure differences and aerodynamic phenomena such as vortices and flow separation to be detected. These phenomena occur often on rotating blades [1]. Based on the results from a feasibility study, a wind tunnel experiment was conducted in the low-speed wind-tunnel BLSWT of AIRBUS in Bremen at propeller rotation speeds up to 14,400 rpm.

Application of Pressure-Sensitive Paint for Determination of Dynamic Surface Pressures on a 30 Hz Oscillating 2D Profile in Transonic Flow

Visualization and measurements of aerodynamic effects on a 2D-wing-profile model were conducted using an optical pressure measurement system based on the pressure-sensitive paint (PSP) technique. The PSP technique can be used to obtain absolute pressure distributions on the surface of a model and in addition to evaluate quantitative aerodynamic flow phenomena e.g., shock location, shock-shock interaction, and shock boundary layer interaction, by using scientific grade cameras and image processing techniques. The PSP technique has been used here for investigations of periodic and unsteady flows. In a wind tunnel campaign in the DNW-TWG, a 2D-wing-profile model, which is pitch oscillating at up to 30 Hz, was investigated. The experiment presented here was performed at angles-of-attack α = 1.12° ± 0.6° at Ma = 0.72. With this work the area of application of PSP to dynamic systems where oscillating pressure changes of the order of 1000 Pa have to be measured at rates of up to 100 Hz is demonstrated.

Application of Temperature and Pressure Sensitive Paints to DLR Hypersonic Facilities: “lessons learned”

PSP and TSP measurements have been carried out on the following DLR facilities: small test shock tube, High Enthalpy Shock Tunnel (both in Gottingen) and the Hypersonic Wind Tunnel (in Cologne). Based on the results from these measurements, various challenges and problem areas could be identified: the role played by these in hindering a quantitative application of PSP/TSP to the facilities is discussed, and ways and means are presented for either overcoming them or at least ameliorating their influence.

Recent developments of image based measurement methods for application to transonic flows in industrial wind tunnels

Abstract The experimental investigation of unsteady complex flow fields in wind tunnels requires advanced measurement techniques. The most important of such image based measurement techniques are those for the measurement of planar flow velocity fields, planar pressure distribution, model location and deformation, model temperature and quantitative high speed flow visualization. The applications as carried out by DLR range from low speed flows to transonic flows, from high lift configurations to propellers and rotors, from wake vortex investigations in catapult facilities and water towing tanks to investigations of vortex break down phenomena on delta wings. The capability to use image based measurement techniques in transonic flows requires dedicated technical developments and experienced scientists due to the special environment of a transonic wind tunnel. In this paper an overview of the state-of-the art of the application of image based measurement techniques in transonic flows as performed by DLRs Institute of Aerodynamics and Flow Technology will be given.

Development of PSP Technique for Application on the VFE-2 65° Delta Wing Configuration

For the International Vortex Flow Experiment 2 (VFE-2) new wind tunnel tests on a NASA delta-wing model by using modern non-intrusive measurement techniques have been performed in the DNW-TWG (Gottingen) transonic wind tunnel. In order to obtain a good understanding of the flow around the wind tunnel model the PSP (Pressure Sensitive Paint) technique has been applied. The PSP technique can be used to realize absolute pressure measurements on the whole surface of a model using scientific grade cameras and advanced image processing techniques. By means of the planar pressure information of the flow topology can be investigated in more detail than would be possible with data of conventional pressure taps. Surface pressures on the entire surface of the model have been obtained using DLRs mobile PSP system, viewing from top and bottom by means of four CCD-cameras. Finally, the measured pressures have been integrated to calculate forces and moments of the full model.

PSP Measurements on a Linear Plug Nozzle: Aerodynamic Investigations on Linear Plug Nozzle Configurations

Pressure field measurements on a Linear Plug Nozzle model were conducted to evaluate the feasibility and accuracy of measurements using DLR’s Pressure Sensitive Paint (PSP) system in the high-speed wind tunnel at Merkers (HWK) of TU-Dresden. A part of the nozzle surface was coated with binary PSP paint. Results show that the optical pressure measurement system with binary paint can be used in the HWK facility. In addition, the paper gives a summary of the thrust vector calculations based on measured static pressure distributions on the plug surface using thrust vector control.

The effect of pressure gradient and a non-adiabatic surface on boundary layer transition investigated by means of TSP

The influence of streamwise pressure gradient and a non-adiabatic wing surface on boundary layer transition was experimentally investigated at the DNW-KRG blow-down wind tunnel facility in Gottingen, Germany. Boundary layer transition was detected non-intrusively by means of the Temperature-Sensitive Paint technique. A new wind tunnel model was designed with the aim of systematically investigating the influence of streamwise pressure gradient and a non-adiabatic wing surface, including Reynolds number effects and Mach number effects, on boundary layer transition. The model was tested at high Reynolds numbers and at a high subsonic Mach number. Favorable, neutral, and unfavorable streamwise pressure gradients were considered and various temperature differences between flow and model surface were implemented. More pronounced negative streamwise pressure gradients and surface temperatures closer to the adiabatic wall temperature were shown to stabilize the boundary layer and allowed larger transition Reynolds numbers to be achieved. The resulting effect of the coupling of streamwise pressure gradient and a non-adiabatic wing surface was found to be strongly dependent on the considered stability situation. The favorable effect on boundary layer transition of surface temperatures closer to the adiabatic wall temperature was shown to be more pronounced for stability situations characterized by a markedly negative pressure gradient.