Ulrich Henne

Transition Detection on Rotating Propeller Blades by means of Temperature-Sensitive Paint

The laminar-to-turbulent boundary-layer transition on a high-speed rotating propeller was measured using Temperature-Sensitive Paint (TSP). The TSP formulation, the experimental set-up, the image acquisition, and processing procedure had been evaluated in a pretest. High resolution propeller images were obtained even at rotation speeds of 9600 rpm. Obtained temperature images clearly show the temperature steps due to the laminar-to-turbulent boundary layer transition. Based on the pretest results, a wind tunnel experiment was conducted in the low-speed wind-tunnel BLSWT of AIRBUS in Bremen at propeller rotation speeds up to 14400 rpm. The TSP results of the wind tunnel test visualized the development of laminar and turbulent regions on the propeller blade depending on propeller speed.

Experimental Study of a Scramjet Nozzle Flow Using the Pressure-Sensitive-Paint Method

An experimental study on scramjet nozzle flows was carried out at the German Aerospace Center. The tests were performed at a free-stream Mach number of 7 in the hypersonic wind tunnel H2K in Cologne. The Reynolds number in the tunnel flow was varied in order to study the performance of the scramjet nozzle at different flight altitudes. The effects of different nozzle pressure ratios were investigated and compared. The static pressure distribution on the single expansion ramp was measured by both the Pressure-Sensitive Paint (PSP) Method and PSI pressure transducers. The PSP method enables one to gain detailed field information about the pressure distribution on the entire nozzle surface. A Pitot rake was used to measure the Pitot pressure distribution in the nozzle wake. The data obtained by the different measurement techniques permitted a characterization of the nozzle flow and gave an insight into the properties of scramjet nozzle flows.

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.

Measurement of Flow Properties and Thrust on Scramjet Nozzle Using Pressure-Sensitive Paint

An experimental study of flows over a single expansion ramp nozzle with flush-mounted side walls was carried out at the DLR, German Aerospace Center. The tests were performed at a freestream Mach number of 7 in the hypersonic wind tunnel H2K in Cologne. The Reynolds number and nozzle pressure ratios in the wind-tunnel flow were varied to study the performance of the scramjet nozzle at different flight altitudes and run conditions. The static pressure distribution on the single expansion ramp was measured by both the pressure-sensitive paint method and by using pressure transducer taps located at discrete points on the surface. These two methods showed that the nozzle pressure ratio and the freestream Reynolds number do not substantially influence the static pressure ratio on the expansion ramp. A pitot rake was also used to measure the pressure distribution in the nozzle wake. Using this technique the nozzle flow in the wake could be visualized and the strong influence of the nozzle pressure ratio on the interaction between nozzle and external flows was revealed. The data obtained by the different measurement techniques permitted a characterization of the nozzle flow and gave insight into the properties of single expansion ramp nozzle flows. The thrust generated by the nozzle, the thrust efficiency coefficient, and the thrust vector angle were calculated by using the pressure data obtained by both pressure measurement techniques and the results compared. It was shown that thrust values obtained from pressure tap measurements were overestimated. Criteria were developed to aid in the design and optimization of the thrust-related performance criteria for this single ramp nozzle.

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.

Nonadiabatic Surface Effects on Transition Measurements Using Temperature-Sensitive Paints

Tests were conducted at the Cryogenic Ludwieg-Tube Gottingen to investigate the influence on onset of boundary-layer transition of thermal gradients on the model surface, whereby the temperature-sensitive paint technique has been used to detect transition. The laminar airfoil under investigation was tested at high Reynolds and at both low and high subsonic Mach numbers. The influence on boundary-layer transition of the temperature difference between the flow and the model surface due to the temperature drop occurring during a test run at the Cryogenic Ludwieg-Tube Gottingen was examined. Various combinations of flow conditions and angles of attack were employed to investigate different stability situations. Linear-stability computations, based on the experimental data, were also carried out. The unfavorable impact of surface temperatures larger than the adiabatic-wall temperature was identified to be dependent on the considered boundary-layer-stability situation. For certain stability situations, it was s...

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.

Combination of Temperature-Sensitive Paint and Carbon Nanotubes for Transition Detection

For transition detection measurement in wind tunnels by means of Temperature-Sensitive Paint (TSP) or InfraRed Thermography (IRT), a sufficient temperature difference between laminar and turbulent boundary layer areas has to be established. If the Temperature difference, naturally occurring under adiabatic wall temperature conditions, is too small to be recognized by IRT or TSP, the magnitude of the temperature change in the laminar-to-turbulent transition area has to be enhanced artificially. Mainly known are two different methods based on heat transfer from the wind-tunnel flow to the model substrate to generate temperature differences: a) Temperature steps in the flow (cooling or heating of the flow) and b) Electrical heating of the model surface (established technique is using heating elements inside the model). A new technique arises from the use of carbon nanotubes (CNT). Materials based on that have a very high electrical heating capability (>1,000 lager than Copper) and can be mixed in a surface coating. Compared to classical heating foils the CNT coating technique has the advantage that a higher spatial homogeneity with respect to heating can be achieved and the applicable thickness of a CNT coating is in the order of micrometers. The presented paper describes the further development of the application of CNT in combination with TSP for transition detection in wind tunnels at high Reynolds numbers.

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.

Influence of non-adiabatic model surface on transition measurements using the Temperature-Sensitive Paint technique in cryogenic wind tunnels

Tests were conducted at the cryogenic blow-down wind tunnel facility DNW-KRG in Gottingen, Germany, with the aim of investigating the influence of the thermal gradients on the model surface on onset of boundary layer laminar-turbulent transition. The laminar airfoil under investigation was tested at high Reynolds and both low and high subsonic Mach numbers. Boundary layer transition was detected non-intrusively by means of the Temperature-Sensitive Paint technique. The effect of the temperature drop occurring during a run at DNW-KRG on the stability of the laminar boundary layer was investigated. Various combinations of flow conditions and angles-of-attack were employed in order to investigate different stability situations. The influence of the temperature difference between flow and model surface on boundary layer transition development was examined. The unfavorable impact of the non-adiabatic thermal boundary condition at the model surface was identified to be dependent on the considered boundary layer stability situation.