Vladimir Ondrus

Flavonoid Glucuronides and a Chromone from the Aquatic Macrophyte Stratiotes aloides

The first phytochemical analysis of the aquatic macrophyte Stratiotes aloides afforded two new flavonoid glucuronides, luteolin 7-O-beta-D-glucopyranosiduronic acid-(1-->2)-beta-D-glucopyranoside (1) and chrysoeriol 7-O-beta-D-glucopyranosiduronic acid-(1-->2)-beta-D-glucopyranoside (2), as well as the new 2-(2-hydroxypentyl)-5-carboxy-7-methoxychromone (5) and chrysoeriol 7-O-beta-(6-O-malonyl)glucopyranoside (3), which has been assigned via NMR data for the first time. Additionally, free amino acids such as tryptophan, arginine, leucine, isoleucine, phenylalanine, and tyrosine along with choline, cis-aconitic acid, the phenolic glycoside alpha-arbutine, the chlorophyll derivative phaeophorbide a, and the flavonoid glycoside luteolin 7-O-beta-(6-O-malonyl)glucopyranoside (4) were isolated. Despite the low quantities obtained in some cases (between 50-300 microg), the structures of all compounds were unambiguously elucidated by extensive NMR and MS experiments. With a delay of 2 days compound 1 (10 and 50 microM test concentration) strongly inhibited the growth of human SH-SY5Y neuroblastoma cells in a dose-dependent manner, whereas only a moderate growth inhibition of human Patu 8902 carcinoma cells could be observed. Compounds 1 and 2 showed no activities against the bacteria Escherichia coli BW25113, Pseudomonas pudida KT2440, and Enterobacter cloacae subsp. dissolvens.

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.

Development of new two-component temperature-sensitive paint (TSP) for cryogenic testing

Two-component temperature-sensitive paint (TSP) for cryogenic wind tunnels has been newly developed to extend the highest working temperature up to 320 K, whereas a conventional single-component cryoTSP operates in the temperature range from 100 to 240 K. The two-component cryoTSP includes two luminophores: a ruthenium complex (Ru(trpy)2) and a europium complex, which are very temperature sensitive in the range of 100–240 K and 220–320 K, respectively. The ruthenium complex is excited by blue light while the europium complex requires UV light. One can thence operate the two luminophores independently by illuminating the paint at different wavelengths. Both luminophores emit red light, so that it is possible to use a single camera filter to observe both luminophores. Verification tests at different cryogenic wind tunnels proved that the two-component cryoTSP could detect a boundary layer transition line even up to room temperatures with only a single coating. This means that it is neither necessary to apply a different TSP coating to a model nor use an infrared camera when the wind tunnel is operated at room temperatures. As a result, the two-component cryoTSP enables one to save time and money in cryogenic testing.

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.

Investigation of Circular Cylinder Flow in Water Using Temperature-Sensitive Paint

In the present investigation the method of Temperature-Sensitive Paint (TSP) is applied to visualize the unsteady pattern of surface flow on an immersed body in water. A ‘waterTSP’ has been developed with high temperature sensitivity in the range 10 °C < T < 40 °C. Experiments were conducted in a recirculating water tunnel where a circular cylinder was used as the test body. The range of the Reynolds number investigated is 3500 < Re < 14500. It is demonstrated that waterTSP is capable of showing unsteady heat flux on the model surface under flow conditions. For example, the footprint and the motion of the separation line can be identified. The dimensionless frequency of vortex shedding (Strouhal number, Sr) is measured from waterTSP images and the dynamics of turbulent near-wall structures are visualized.

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.

Pressure Gradient and Nonadiabatic Surface Effects on Boundary Layer Transition

The influence of the streamwise pressure gradient and a nonadiabatic surface on boundary layer transition was experimentally investigated at the Cryogenic Ludwieg-Tube Gottingen, Germany. Boundary layer transition was detected nonintrusively by means of the temperature-sensitive paint technique. The wind-tunnel model was designed to achieve a quasi-uniform streamwise pressure gradient over a large portion of the model chord length. This allowed the effects on boundary layer transition of the streamwise pressure gradient and wall temperature ratio to be decoupled. The model was tested at high Reynolds numbers and at a high subsonic Mach number. Favorable, almost-zero, and adverse streamwise pressure gradients were considered; and various temperature differences between the flow and the model surface were implemented. Stronger flow acceleration and lower wall temperature ratios led to an increase of the transition Reynolds number. Larger increases in the transition Reynolds number were obtained at more pron...

Application of Lifetime-based Pressure-Sensitive Paint Technique to Cryogenic Wind Tunnel Tests

The capability of a lifetime-based Pressure-Sensitive Paint (PSP) method for application in cryogenic wind tunnels was investigated. The relevant experiments were conducted in the Pilot-European Transonic Windtunnel (PETW). The 2D airfoil model (CAST10-II) was painted with PtTFPP/PTMSP paint and tested in a nitrogen atmosphere at 150 K. PSP and pressure tap data were acquired at Mach 0.78 at a total pressure of 160 kPa. The oxygen concentration of the flow was set to 1000 ppm by continuously supplying dry air. As a result, the lifetime-based PSP method successfully visualized the pressure distribution on the airfoil model under cryogenic conditions. The quantitative agreement of PSP and pressure tap data was obtained and the difference in both data came out to be 0.05 in the pressure coefficient Cp. The accuracy of PSP data is comparable to results achievable at ambient conditions. Therefore, it may be concluded that the lifetime-based method was successfully applied under cryogenic conditions. In addition to the lifetime-based method, the intensity-based method was also conducted as a comparison. Furthermore the applicability of the lifetimebased method to tests with model deformation was evaluated.

Development of a Highly Sensitive Temperature-Sensitive Paint for Measurements under Cryogenic Temperatures (100 – 160 K) Conditions

A new temperature-sensitive paint (TSP) was developed to capture images with high signal-to-noise ratio in wind tunnel tests under cryogenic temperature (100 – 160 K) conditions. Typical applications of TSP are the detection of boundary-layer transition and the measurement of the temperature distribution on the model surface. Conventional TSPs based on Ru(terpy)_2Cl_2 as the temperature-sensitive luminophore have temperature sensitivities of less than 2 %K^-1 at 130 K. This sensitivity is not sufficient enough for TSP measurements in large industrial wind tunnels without considerable post-processing effort. The newly developed TSPs achieved a temperature sensitivity of about 4 %K^-1 at 130 K. Experiments were conducted in the cryogenic low-speed wind tunnel of the German-Dutch Wind Tunnel organization to evaluate the capability of these TSPs to detect boundary-layer transition. The new TSP formulations were proven to be capable to resolve small temperature differences and thereby detect boundary-layer transition with high accuracy.