Numerical Analysis of Viscoelastic Flow Based on FENE-P Model using High-order Accuracy Finite Difference Method

This work is to develop the FENE-P model by using a high-order accuracy finite difference method. We performed an effective numerical simulation scheme with the upwind difference method, to solve the polymer additive solution in the channel flow. In constitutive equation, the 3rd-order accurate upwind difference scheme was applied and steady resolution was achieved

Investigation of frequency-domain lifetime imaging technique (FLIM-PSP/TSP) in DLR

Last several years, the applicability of frequency-domain fluorescence lifetime imaging (FLIM) with a newly developed CMOS camera sensor (pco.flim) to Pressure- and Temperature-Sensitive Paint (PSP/TSP) measurements has been investigated by DLR in collaboration with Kumamoto University and Tohoku University. The investigations were widely conducted such as a preliminary camera and LED operation check, parametric study in the calibration chamber, camera calibration, demonstration test with an impinging jet to a PSP coated plate, low-speed and transonic wind tunnel tests. This oral presentation introduces the principle part of the FLIM technique and the overview of our collaborative works

Investigation of frequency-domain lifetime PSP technique using a Fluorescence Lifetime Imaging (FLIM) camera

Frequency-domain fluorescence lifetime imaging (FLIM) is applied for acquiring pressure sensitive paint (PSP) images by using a pco.flim camera, which has an in-pixel dual tap control CMOS image sensor. In this FLIM technique, an excitation light is modulated sinusoidally, and modulation depth and phase angle, which depend on lifetime or pressure, are estimated from four gated images. In the calibration test, the influences of modulated excitation light, exposure time and modulation frequency are shown. The pressure sensitivity of phase angle has similar sensitivity to that in the standard lifetime method (gated intensity ratio). As the first step of application, a low speed wind tunnel test was performed. The pressure distribution caused by the vortex on a delta wing is visualized successfully by this technique

A Sine-Modulated High-Intensity UV-LED Light Source for Pressure-Sensitive Paint (PSP) Application using Fluorescence Lifetime Imaging (FLIM) technique

Pressure-Sensitive Paint (PSP) measurement technique is based on the change of the intensity or decay time of its luminescence with pressure, brought about by oxygen quenching. For the so called “lifetime method” the pressure dependent luminescence decay time must be detected. Two approaches exist for this type of measurement: The time-domain lifetime method, for which a light pulse is used to excite the paint and the pressure dependent time constant is determined from the decay curve, and the frequency-domain based lifetime method, where sinusoidal modulated light is used to excite the paint and the emission light is used to calculate the pressure dependent phase shift and amplitude ratio. A new CMOS image sensor has been developed by CSEM and PCO used in the pco.flim camera for fluorescence lifetime imaging (FLIM) microscopy. The camera provides a sinusoidal voltage output for controlling an excitation light source. In this study, a high-intensity LED system was developed by DLR and HARDsoft providing a sine wave output of UV light for excitation of PtTFPP based PSP on larger scale surfaces like wind tunnel models using the pco.flim camera. This system, called illuminator, has been designed around a single, high-power LED emitting UV light of 390 nm. This LED has been specified for CW operation with a supply current of up to 18 A. However, it has been proven that this LED works with a satisfied linearity in the range up to 10 A, providing a maximum radiometric flux of about 11.5 W. The illuminator can be operated with CW or sine modulation. For the sine modulation it can be driven by a sine signal of 1 Vp-p directly from the FLIM camera in the range of 5-50 kHz. In calibration tests using small samples coated with PSP, the influences of parameters like amplitude and frequency of excitation light on the pressure sensitivity of phase angle and amplitude ratio are shown. Results from a test on a delta wing in the 1m low speed wind tunnel of DLR Göttingen

A Sine-Modulated High-Intensity UV-LED Light Source for Pressure-Sensitive Paint (PSP) Application using Fluorescence Lifetime Imaging (FLIM) technique

Pressure-Sensitive Paint (PSP) measurement technique is based on the change of the intensity or decay time of its luminescence with pressure, brought about by oxygen quenching. For the so called “lifetime method” the pressure dependent luminescence decay time must be detected. Two approaches exist for this type of measurement: The time-domain lifetime method, for which a light pulse is used to excite the paint and the pressure dependent time constant is determined from the decay curve, and the frequency-domain based lifetime method, where sinusoidal modulated light is used to excite the paint and the emission light is used to calculate the pressure dependent phase shift and amplitude ratio. A new CMOS image sensor has been developed by CSEM and PCO used in the pco.flim camera for fluorescence lifetime imaging (FLIM) microscopy. The camera provides a sinusoidal voltage output for controlling an excitation light source. In this study, a high-intensity LED system was developed by DLR and HARDsoft providing a sine wave output of UV light for excitation of PtTFPP based PSP on larger scale surfaces like wind tunnel models using the pco.flim camera. This system, called illuminator, has been designed around a single, high-power LED emitting UV light of 390 nm. This LED has been specified for CW operation with a supply current of up to 18 A. However, it has been proven that this LED works with a satisfied linearity in the range up to 10 A, providing a maximum radiometric flux of about 11.5 W. The illuminator can be operated with CW or sine modulation. For the sine modulation it can be driven by a sine signal of 1 Vp-p directly from the FLIM camera in the range of 5-50 kHz. In calibration tests using small samples coated with PSP, the influences of parameters like amplitude and frequency of excitation light on the pressure sensitivity of phase angle and amplitude ratio are shown. Results from a test on a delta wing in the 1m low speed wind tunnel of DLR Göttingen

Investigation for Simultaneous Measurement of Pressure and Temperature Using Frequency-Domain Lifetime Imaging Technique

There are two methods for measuring pressure using conventional pressure-sensitive paints (PSP). The first one is the intensity method using constant excitation light. The second one is the lifetime method using pulsed light. The pressure distribution on body surface is obtained by measuring the emission intensity and the lifetime depending on the pressure, respectively. If the temperature distribution changes due to heat generated by an excitation light and a flow, or heat from an external element such as a motor, it is necessary for high-accuracy pressure measurement to correct the temperature in the both methods. Therefore the temperature data is additionally acquired by a temperature sensor. In this study, frequency–domain lifetime imaging technique (FLIM-PSP) is investigated using sinusoidaly modulated light. The emission intensity is also modulated with same frequency of the light. But the modulated emission wave has the phase angle, the modulation amplitude and average intensity depend on the pressure and the temperature. That is, since FLIM-PSP technique has plural variables, it is investigated that simultaneous measurement of temperature and pressure is possible. It is shown that the phase angle and the modulation depth, which represents a ratio of the modulation amplitude to the averaging intensity, depend on pressure and temperature in a calibration test, as shown in the figure. It is shown that FLIM-PSP technique has possibility of a simultaneous pressure and temperature measurement based on the different sensitivity to pressure and temperature in the phase angle and the modulation depth