Temperature Sensitive Paint Research Articles

Use of Rib Turbulators to Enhance Postimpingement Heat Transfer for Curved Surface

The present study aims to investigate the heat transfer and pressure loss characteristics for multiple rows of jets impinging on a curved surface in the presence of rib turbulators. The target plate contains a straight section downstream of the impingement section. The rib turbulators are added only over the straight section, in an attempt to enhance the heat transfer while minimizing the pressure loss. The jet plate configuration in this study has fixed jet hole diameters and hole spacing. For the curved plate, the radius of the target plate is 32 times the diameter of the impingement holes. Impingement array configuration was chosen such that validation and comparison can be made with the open literature. For all the configurations, crossflow air is drawn out in the streamwise direction. Average jet Reynolds numbers ranging from 55,000 to 125,000 were tested. Heat transfer characteristics are measured using steady-state temperature-sensitive paint (TSP) to obtain local heat transfer distribution. The experimental results are compared with computational fluid dynamics (CFD) simulations. CFD results show that CFD simulations predict the heat transfer distribution well in the postimpingement area with turbulators.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D = 31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction, which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 55,000 to 125,000 are tested. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2 − f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius and the decay of heat transfer after the impingement section, and to check the open literature correlations. It was found that the target wall curvature did not cause any significant changes in either the flow distribution or the heat transfer level. Comparisons with established correlations show similar level but different trends in heat transfer, potentially caused by differences in L/D. CFD results were able to show agreement in streamwise pitch-averaged Nusselt number levels with experimental results for the curved target plate at higher Re numbers.

Experimental Study on Aerodynamic Heating Induced by Dual Injections into Hypersonic Cross Flow

In this study, the distribution of surface heat transfer induced by dual side-jets injected into a hypersonic flow has been visualized using a temperature sensitive paint. The experiments were performed in both tandem and parallel injector arrangements, and the spacing between the injection holes was taken as a parameter in each arrangement. As a result, the aerodynamic heating in the separated region of the boundary layer and in the horseshoe vortex was clearly visualized. In the tandem arrangements, heat transfer remarkably increased immediately upstream of the front injector. The distributions and the intensity of surface heat transfer were similar to those caused by the single injection. On the other hand, in the parallel arrangements, the extent of the separation nearly doubled, and the maximum heat flux decreased to less than half of that from the single injection. The global distribution of heat transfer varied significantly as the injector spacing was changed. When the injectors were positioned with a large spacing, the interaction between the side-jets was relatively lowered, and thus distribution, as for the single injector, was induced around each injection hole individually. In contrast, with a short spacing, the dual injection behaved as a single obstacle. The most effective reduction of maximum heat flux was achieved with an intermediate injector spacing.

Boundary-Layer Detection at Cryogenic Conditions Using Temperature Sensitive Paint Coupled with a Carbon Nanotube Heating Layer.

Detection of flow transition on aircraft surfaces and models can be vital to the development of future vehicles and computational methods for evaluating vehicle concepts. In testing at ambient conditions, IR thermography is ideal for this measurement. However, for higher Reynolds number testing, cryogenic facilities are often used, in which IR thermography is difficult to employ. In these facilities, temperature sensitive paint is an alternative with a temperature step introduced to enhance the natural temperature change from transition. Traditional methods for inducing the temperature step by changing the liquid nitrogen injection rate often change the tunnel conditions. Recent work has shown that adding a layer consisting of carbon nanotubes to the surface can be used to impart a temperature step on the model surface with little change in the operating conditions. Unfortunately, this system physically degraded at 130 K and lost heating capability. This paper describes a modification of this technique enabling operation down to at least 77 K, well below the temperature reached in cryogenic facilities. This is possible because the CNT layer is in a polyurethane binder. This was tested on a Natural Laminar Flow model in a cryogenic facility and transition detection was successfully visualized at conditions from 200 K to 110 K. Results were also compared with the traditional temperature step method.

Experimental study of heat transfer enhancement with segmented flow in a microchannel by using molecule-based temperature sensors

This paper presents an experimental study of heat transfer enhancement with liquid-gas two-phase segmented microchannel flows by utilizing a novel technique of molecule-based temperature sensors. A serpentine microchannel was constructed and steady liquid and gas segments of ethanol and air were successfully produced at various flow rates. A molecule-based temperature sensor made of Tris(2,2′-bipyridyl) ruthenium was utilized in the liquid segments by dissolving in ethanol as temperature-sensitive fluid and mixing in a dope to produce temperature-sensitive paint in order to retrieve fluid and surface temperature data, respectively. Three cases of different liquid and gas flow rates were tested. The heat transfer enhancements of these three cases were carefully examined under constant heat flux thermal boundary conditions, and the increased heat transfer was evaluated in comparison with the single-phase flow, where only liquid was injected in the microchannel. An improvement of up to 30% in the averaged Nu number of the microchannel flow was determined for Case 3, with a high gas flow rate and short liquid segments. Velocity and vorticity profiles in the liquid segments at different gas and liquid flow rates were also studied using a micro-particle image velocimetry technique. Stronger circulation was observed in Case 3, which confirmed the results from the heat transfer analysis, namely that more efficient heat transfer occurs with strong circulation in short liquid segments when a high gas flow rate is applied. The results of the present study provide detailed temperature profiles in segmented flow as well as the evolution of the Nu number from the entrance to the exit of a serpentine microchannel.

Global and local skin friction diagnostics from TSP surface patterns on an underwater cylinder in crossflow

A systematical method is formulated for extracting skin-friction fields from Temperature Sensitive Paint (TSP) images in the sense of time-averaging and phase-averaging. The method is applied to an underwater cylinder in crossflow at two subcritical regimes (Re = 72 000 and 144 000). TSP maps are decomposed in a time-averaged, a phase-averaged, and a random component. The asymptotic form of the energy equation at the wall provides an Euler-Lagrange equation set that is solved numerically to gain the relative skin friction time- and phase-averaged fields from the TSP surface temperature maps. The comparison of the time averaged relative skin-friction profiles with the literature data shows an excellent agreement on the whole laminar boundary layer up to the laminar separation line. Downstream of separation, time averaged results identify the secondary reattachment/separation events, which are lost in the available literature data. The periodic behavior of the skin-friction is taken, describing how the laminar separation bubble evolves by providing the time history of the laminar separation line and of the secondary reattachment/separation over the entire vortex shedding period. Instantaneous skin friction maps reveal the existence of coherent structures by capturing their footprint on the cylinder’s surface. An array of Π-shaped traces marks the existence of counter-rotating, streamwise-oriented vortices just before the laminar separation line. Their interaction with the laminar boundary layer and with the separation line is briefly described. An example of the intermittent excerpt of their influence through the laminar separation line is reported.

Simultaneous PSP and TSP measurements of transient flow in a long-duration hypersonic tunnel

The current work presents simultaneous measurements of transient flow using fast-responding pressure- and temperature-sensitive paints in a long-duration hypersonic tunnel; the pressure, temperature and heat flux fields were obtained on a standard model (HB-2) at Ma = 5. Fast PSP and TSP were applied symmetrically on the model with low thermal conductivity. Both coatings were illuminated by a UV-LED, and unsteady pressure and temperature data were recorded at 500 Hz using a high-speed camera. Time-dependent temperature correction was applied on the PSP data based on the TSP results, while the heat flux was calculated from the time-resolved temperature fields using a 1D semi-finite heat conduction model. The temperature-induced errors in PSP data were effectively removed by the current compensation method. The pressure and heat flux results showed good agreement with the reference data from previous studies. The key events throughout the hypersonic tunnel run were captured by the unsteady PSP/TSP data, including the tunnel start-up, the flow build-up, the steady flow period and the tunnel shutdown. The differences caused by the change of attack angle were also clearly recognized. The current PSP/TSP system has shown great potential for unsteady flow diagnostics in hypersonic flows.

Measurement of flow structures and heat transfer behind a wall-proximity square rib using TSP, PIV and split-fiber film

In the present study, complementary measurement techniques—temperature sensitive paint (TSP), planar particle image velocimetry (planar PIV) and a split-fiber film probe—were used to investigate the effects of a “wall-proximity square rib” on flow structure and surface heat transfer augmentation. TSP was used to measure the time-averaged wall temperature field at three different Reynolds numbers ( $$ Re_{d} $$ = 3800, 7600 and 11,400) based on the rib height d and the mainstream velocity $$ U_{o} $$ , and wall-proximity configurations with four different gap ratios (gap size $$ G $$ over rib height d), G/d = 0, 0.25, 0.50 and 0.75. The two-dimensional distribution of the normalized Nusselt number convincingly demonstrated the existence of a hot spot immediately behind the rib in the attached rib configuration (G/d = 0) and surface heat transfer augmentation in the reattachment zone. Among the three wall-proximity configurations, G/d = 0.25 resulted in maximum heat transfer augmentation immediately behind the rib and overall improvement in surface heat removal. However, no distinctly different spatial patterns of the normalized Nusselt number distribution were found at the three different Reynolds numbers. A subsequent experiment examined the flow pattern and flow structures at $$ Re_{d} $$ = 7600 and three wall-proximity configurations (G/d = 0, 0.25 and 0.50). Velocity field measurements using PIV, along with complementary measurements using split-fiber film, gave a clear view of the flow pattern behind the rib; a very slender separation bubble with highly unsteady flow reversal was found close to the surface when G/d = 0.25. For configurations with G/d = 0.25 and 0.50, the high-speed jet issuing from the gap had a complicated influence on the interaction between the upper free shear layer and lower strong shear layer, resulting in slanted movement of the coupled wake flow. Proper orthogonal decomposition was used to identify the spatial characteristics of the superimposed flow structures. In the configuration G/d = 0.25, coherent structures were found throughout most of the wake region, beginning roughly 1.2d behind the rib. Fluid flow in the region near the wall was strongly influenced by the dominant coherent structures, which were evidently the main mechanism for surface heat removal. In the configuration with G/d = 0.50, the area with large velocity fluctuation intensity shifted away from the wall toward the mainstream due to rapid expansion of the wall jet. This, in combination with large-scale coherent structures from the surface, meant a much reduced influence on the fluid near the wall and a corresponding deterioration of surface heat transfer beyond the station x/d = 4 (x being the downstream distance from the rib’s trailing edge).

An optical-chemical sensor using rhodamine B on anodized-aluminum for surface temperature measurement from 150 to 500 K

Temperature-sensitive paint (TSP) provides surface temperature measurements over the surface of a test body. It can be used to obtain surface temperature measurements which can be also useful in determining heat flux and visualizing the location of boundary layer transition. In this study, a rhodamine B (RhB)-based anodized-aluminum temperature-sensitive paint (AA-TSP) is developed as a surface temperature sensor. Anodized aluminum offers advantages over a polymer base, including an increased melting point and increased resistance to stiffening and cracking at cryogenic temperatures, making it well-suited for wide range temperature measurements. In this study, the influence of different dipping solvents to apply the RhB onto the anodized-aluminum is characterized. Two groups of dipping solvents were found with respect to the luminescent intensity and temperature sensitivity based on the polarity index of the solvents. By using anodized-aluminum as opposed to a polymer as the platform for the RhB, the sensor provides an expanded temperature detection range from 150 to 500K. The highest temperature sensitivity given by the AA-TSP approached −3%/K at 150K, which is determined by fitting a sigmoidal curve to the temperature calibration results.

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 Göttingen, 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 pronounced flow acceleration for the same reduction in the wall temperature ratio. The measured pressure distributions served as input for boundary layer stability computations, performed according to compressible, linear, local stability theory under the (quasi-) parallel-flow assumption. Amplification factors of the Tollmien–Schlichting waves were shown to be reduced by stronger favorable pressure gradients and lower wall temperature ratios, which was in agreement with the observed variation in the transition Reynolds number.

Phenomenology of a flow around a circular cylinder at sub-critical and critical Reynolds numbers

In this work, the flow around a circular cylinder is investigated at Reynolds numbers ranging from 79 000 up to 238 000 by means of a combined acquisition system based on Temperature Sensitive Paint (TSP) and particle velocimetry. The proposed setup allows simultaneous and time-resolved measurement of absolute temperature and relative skin friction fields onto the cylinder surface and near-wake velocity field. Combination of time-resolved surface measurements and planar near-field velocity data allows the investigation of the profound modifications undergone by the wall shear stress topology and its connections to the near-field structure as the flow regime travels from the sub-critical to the critical regime. Laminar boundary-layer separation, transition, and re-attachment are analyzed in the light of temperature, relative skin friction maps, and Reynolds stress fields bringing about a new perspective on the relationship between boundary layer development and shear layer evolution. The fast-responding TSP employed allows high acquisition frequency and calculation of power spectral density from surface data. Correlation maps of surface and near-wake data provide insight into the relationship between boundary-layer evolution and vortex shedding. We find that as the Reynolds number approaches the critical state, the separation line oscillations feature an increasingly weaker spectrum peak compared to the near-wake velocity spectrum. In the critical regime, separation line oscillations are strongly reduced and the correlation to the local vorticity undergoes an overall decrease giving evidence of modifications in the vortex shedding mechanism.

Experimental study of unsteady aerothermodynamic phenomena on shock-tube wall using fast-response temperature-sensitive paints

This paper describes an experimental study that used a fast-response temperature-sensitive paint (TSP) to investigate the unsteady aerothermodynamic phenomena occurring on a shock-tube wall. To understand these phenomena in detail, a fast-response TSP with high temperature sensitivity developed for transient temperature measurement was applied to the wall. The shock-tube experiment was carried out under the over-tailored condition, with a pressure ratio of 110 for test gases of air in driver/driven tubes. The following aspects were clarified using the TSP: (a) the TSP could be used to visualize the unsteady aerothermodynamic phenomena and estimate the quantitative heat flux on the shock-tube wall; (b) an x-t diagram based on the TSP response showed shock-tube wall characteristics that included the incident/reflected shocks, laminar-to-turbulent boundary-layer transition, streaks in the turbulent boundary layer, reflected shock/turbulent boundary layer interaction, and waves reflected from a contact surface; (c) the TSP graphically showed that a transition front from the plate’s leading edge and turbulent spots moved with 80% of the free-stream velocity behind the incident shock. In addition, the TSP could track the growth of the turbulent spots on the wall.

Experimental Evaluation of Large Spacing Compound Angle Full-Coverage Film Cooling Arrays: Adiabatic Film Cooling Effectiveness

Adiabatic film cooling effectiveness contours are obtained experimentally with the use of temperature sensitive paint (TSP) on low thermal conductivity film cooled surfaces. The effects of blowing ratio, surface angle, and hole spacing are observed by testing four full-coverage arrays composed of cylindrical staggered holes all compounded at 45 deg, which parametrically vary the inclination angles, 30 deg and 45 deg, and the spacing of the holes 14.5 and 19.8 times the diameter. Local film cooling effectiveness is obtained throughout these largely spaced arrays to 23 rows for the 19.8 diameter spacing array and 30 rows for the 14.5 diameter spacing array. The coolant takes several rows to merge and begin to interact with lateral holes at these large spacings; however, at downstream rows the film merges laterally and provides high effectiveness in the gaps between injections. At low blowing, each individual jet remains discrete throughout the array. At higher blowing rates, the profile is far more uniform due to jets spreading as they reattach with the wall. Laterally averaged values of effectiveness approach 0.3 in most cases with some high blowing low spacing, even reaching 0.5.

インクジェットプリンタ PSP を用いた噴流場の可視化計測

Pressure-sensitive paint (PSP) is an optical and non-intrusive pressure measurement technique, and is used in wind tunnel testing. In general, PSP is applied to a model surface by a sprayer by hand, resulting in non-uniform layer. Recently, we proposed a novel PSP paint technique using an inkjet printer. This technique enable us to easily paint uniform PSP. In this study, we fabricated a combined PSP and TSP (temperature-sensitive paint) by inkjet printer. PSP and TSP were symmetrically painted on a substrate. Then, we measured the pressure and temperature distribution induced by impingement jet. The obtained pressure distribution was in good agreement with the literature.

Measurements by Temperature Sensitive Paint on Flexible and Deforming Model in Hypersonic Flow

Measurements by Temperature Sensitive Paint on Flexible and Deforming Model in Hypersonic Flow

高温衝撃風洞 HIEST における感温塗料計測技術を用いた空力加熱計測技術の現状

高温衝撃風洞 HIEST における感温塗料計測技術を用いた空力加熱計測技術の現状

感温塗料を用いた赤外線ー可視光変換型熱イメージングデバイス

This paper reports optical read-out thermal imaging devices based on IR-to-visible conversion technique using temperature sensitive phosphor (Eu(TTA)3). Infrared emit from the observation object induces temperature change of a thermally isolated microstructure, of which the temperature can be read out by the luminescence intensity of Eu(TTA)3. Two types of imaging devices were fabricated and evaluated, one of which was made of vacuum deposited Eu(TTA)3 on a deep reactive ion etched thermal isolation structure, and the other was made using photo-patternable temperature sensitive paint combined with a transfer method. Both device can detect the temperature distribution, however the device using vacuum deposited Eu(TTA)3 had a better performance which can detect a human.

210 感温塗料を用いた形状記憶合金表面の温度分布計測(GS2-3 感温塗料・感圧塗料)

210 感温塗料を用いた形状記憶合金表面の温度分布計測(GS2-3 感温塗料・感圧塗料)

Shock wave boundary layer interaction on suction side of compressor profile in single passage test section

The shock wave boundary layer interaction on the suction side of transonic compressor blade is one of the main objectives of TFAST project (Transition Location Effect on Shock Wave Boundary Layer Interaction). In order to investigate the flow structure on the suction side of a profile, a design of a generic test section in linear transonic wind tunnel was proposed. The experimental and numerical results for the flow structure investigations are shown for the flow conditions as the existing ones on the suction side of the compressor profile. Near the sidewalls the suction slots are applied for the corner flow structure control. It allows to control the Axial Velocity Density Ratio (AVDR), important parameter for compressor cascade investigations. Numerical results for Explicit Algebraic Reynolds Stress Model with transition modeling are compared with oil flow visualization, schlieren and Pressure Sensitive Paint. Boundary layer transition location is detected by Temperature Sensitive Paint.

Fast-response underwater TSP investigation of subcritical instabilities of a cylinder in crossflow

We investigate the classic cylinder in crossflow case to test the effectiveness of a fast-response underwater temperature-sensitive paint coating (TSP) in providing highly resolved spatial and time observations of the action of a flow over a bluff body surface. The flow is investigated at Reynolds number <190 k, before the onset of the drag-crisis state. The obtained TSP image sequences convey an accurate description of the evolution of the main features in the fluid–cylinder interaction, like the separation line position, the pattern of the large coherent structures acting on the cylinder’s surface and the small-scale intermittent streamwise arrays of vortices. Ad hoc data management and features extraction techniques are proposed which allow extraction of quantitative data, such as separation line position and vortex-shedding frequency, and results are compared to the literature. Use of TSP for water applications introduces an interesting point of view about the fluid–body interactions by focusing directly on the effect of the flow on the model surface.