Temperature Sensitive Paint Technique Research Articles

A comprehensive heat transfer investigation for impingement/effusion cooling under crossflow conditions

Impingement/effusion cooling is regarded as a highly efficient cooling structure and has been widely adopted in various energy-dependent scenarios. It often exhibits crossflow phenomena due to design or concurrent factors. However, quantifying the individual heat transfer contributions of each cooling structure in impingement/effusion cooling under crossflow conditions remains unclear. In this study, the pressure-sensitive paint and temperature-sensitive paint techniques were adopted to separately evaluate the performance of effusion and impingement cooling under crossflow conditions for a comprehensive heat transfer investigation. Different coolant flow rate (normalized as Rejet = 10,000 to 25,000) and crossflow flow rates (normalized as CMR = 0 to 0.3) were examined. In effusion cooling, cooling effectiveness generally decreased with higher Rejet but improved with increased CMR, except for Rejet = 10,000 and 15,000 with CMR ≥ 0.25, where excessive crossflow coolant negatively affected cooling effectiveness. When comparing cooling effectiveness at the same blowing ratio, higher Rejet with crossflow consistently outperformed, with the maximum improvement reaching 11.55 %. In impingement cooling, the Nusselt number (Nu) increased with Rejet due to enhanced impingement momentum. Crossflow had a detrimental effect at Rejet = 10,000 but showed improvements at Rejet = 15,000 to 25,000. With increasing Rejet, heat transfer performance became less sensitive to varying CMR. Compared to cases without crossflow, the Nu increments at CMR = 0.25 were -5.01 %, 4.03 %, 3.53 %, and 2.64 % for Rejet = 10,000 to 25,000, respectively. It was revealed that crossflow was influential on the impingement cooling, meanwhile, highly influential on the effusion cooling. This study intended to provide a more comprehensive understanding of impingement/effusion cooling and assistance in designing more efficient and tailored cooling strategies for high-performance energy systems.

Review of Development and Comparison of Surface Thermometry Methods in Combustion Environments: Principles, Current State of the Art, and Applications

Temperature is one of the most important parameters in the combustion processes. Accurate surface temperature can help to gain insight into the combustion characteristics of various solid or liquid fuels, as well as to evaluate the operating status of combustion power facilities such as internal combustion engines and gas turbines. This paper mainly summarizes and compares the main surface thermometry techniques, from the aspects of their principles, current state of development, and specific applications. These techniques are divided into two categories: contact-based thermometry and non-intrusive thermometry. In contact-based thermometry, conventional thermocouples as well as thin-film thermocouples are introduced. These methods have been developed for a long time and are simple and economical. However, such methods have disadvantages such as interference to flow and temperature field and poor dynamic performance. Furthermore, this paper reviews the latest non-intrusive thermometry methods, which have gained more interest in recent years, including radiation thermometry, laser-induced phosphorescence, liquid crystal thermography, the temperature-sensitive paint technique, and the temperature-indicating paint technique. Among them, we highlighted radiation thermometry, which has the widest measurement ranges and is easy to acquire results with spatial resolution, as well as laser-induced phosphorescence thermometry, which is not interfered with by the emissivity and surrounding environment, and has the advantages of fast response, high sensitivity, and small errors. Particularly, laser-induced phosphoresce has attracted a great deal of attention, as it gets rid of the influence of emissivity. In recent years, it has been widely used in the thermometry of various combustion devices and fuels. At the end of this paper, the research progress of the above-mentioned laser-induced phosphorescence and other techniques in recent years for the surface thermometry of various solid or liquid fuels is summarized, as well as applications of combustion facilities such as internal combustion engines, gas turbines, and aero engines, which reveal the great development potential of laser-induced phosphorescence technology in the field of surface thermometry.

Boundary Layer Transition Prediction on Planar Turbine Cascade Using Temperature-Sensitive Paint and Numerical Simulation

Advanced measurement technology on boundary layer transition is an effective means to study the flow mechanism and the performance of the cascade. In this research, to investigate the boundary layer transition of transonic VKI-RG turbine cascade, a noncontact measurement technique named temperature-sensitive paint (TSP) that is capable of quantitatively measuring the surface temperature of a model is used. Under the conditions of outlet Mach number (Ma2) = 0.4, 1.03, and 1.2, the transitional location of a cascade is accurately measured by TSP technique. Moreover, a numerical study on the transitional location of a planar cascade was conducted with the conditions of Mach number (Ma) and attack angle (α). The numerical results show that the transitional location moved forward with the increase in Ma2 and α at Ma2 < 1; otherwise, the transitional location moved backward with increasing Ma2 (Ma2 > 1). Lastly, a strong adverse pressure gradient was formed behind the shock wave, which led to the beginning of the transition.

Temperature and skin-friction maps on a lifting hydrofoil in a propeller wake

There are at least two direct links between the friction acting on the surface of a (slightly warmer or colder) body under the influence of an incompressible flow and the temperature distribution on the surface of the body itself. The first relies on the energy equation, which connects the evolution of the temperature distribution at the wall to the action of the skin-friction field. On the other hand, the equation of passive transport of temperature perturbations at the wall unveils a direct relationship between the celerity of propagation of thermal blobs and the friction velocity. Grounding on these relationships, this paper reports about the application of different methodologies, developed to determine skin-friction fields from surface temperature maps, to the analysis of the complex flow evolution on a lifting NACA 0015 hydrofoil immersed in a non-uniform, unsteady wake induced by a marine propeller. The adopted temperature-sensitive paint technique allows obtaining the global temperature data with the appropriate, high resolution in space and time. The approach based on the energy equation leads to an unconventional, single-snapshots optical-flow-like methodology, which allows obtaining time-resolved, relative skin-friction fields. The two approaches based on the displacement of the wall temperature perturbations enable the determination of time- and phase-averaged, quantitative skin-friction fields. One approach grounds on a classical tracking of the thermal disturbances via optical flow, the other one relies on minimizing the discrepancy between the celerity of propagation of thermal fluctuations and the behavior expected according to the Taylor hypothesis. The analysis of the skin-friction fields obtained via the three uncorrelated, complementary approaches discloses the evolution and the mutual interaction of different flow structures (manifolds) over the hydrofoil surface at lifting and zero-lift conditions: the hub and tip vortices, the blade wake, the laminar separation bubble, and the separation at trailing edge.

Enhanced impingement cooling of a circular jet using a piezoelectric fan

The present study explored and examined the piezoelectric (PE) jet: an active cooling concept that can be actuated in demand, which had an oscillating flow and extremely low power consumption. The heat transfer and flow characteristics of the PE jet were quantified at various Reynolds numbers (Re = 5000, 10,000, 18,000) and spacings (H/D = 4.5, 5.5, 6.5; corresponding gap G/D = 0.1, 1.1, 2.1). The temperature sensitive paint technique was used to study the heat transfer, and the particle image velocimetry technique was applied to resolve the flow characteristics and to further correlate the heat transfer results. Measured results show that the impingement cooling of the PE jet increased as the Re increased and as the H/D decreased. Compared with a circular jet, the PE jet exhibited a greatly improved heat transfer at H/D = 4.5 (i.e., G = 0.1D), with a maximum of 20% enhancement in area-averaged Nu. Due to the fan oscillation, the turbulent kinetic energy level in the PE jet was significantly higher than in the circular jet, which greatly promoted the heat transfer at a narrow gap. In general, the new PE jet can provide superior heat transfer performance at a small gap and a high Reynolds number.

Assessment of film cooling’s surface quantities using pressure- and temperature-sensitive paint: Comparisons between shaped and sand-dune inspired holes

Following the previous work (Zhou and Hu, 2017), a comprehensive assessment was performed to further evaluate the film cooling’s surface quantities behind shaped and sand dune-inspired holes. Adiabatic film cooling effectiveness, heat transfer coefficient, and net heat flux reduction (NHFR) were measured at four blowing ratios (M = 0.40, 0.90, 1.40, and 2.00). The measured quantities were compared side-by-side between the shaped and sand dune-inspired holes. The pressure-sensitive paint (PSP) technique was used to acquire high-resolution adiabatic effectiveness and the temperature-sensitive paint (TSP) technique was used to map the corresponding heat transfer coefficient over the surface. Nitrogen and air, with a density ratio of about one, were used as the coolant for the PSP and TSP tests respectively. The measured results showed that the adiabatic effectiveness of the Barchan dune-shaped injection compound (BDSIC) was significantly higher than that of the shaped hole. Improvements of 20–150% in the centerline and 30–400% in the laterally averaged effectiveness were observed behind the BDSIC compared to the shaped hole. As for the heat transfer performance, although the BDSIC showed 10–20% higher heat transfer coefficient, hf/h0, the measured spatially averaged NHFR still demonstrated an augmentation of 50–150% in heat flux reduction in comparison to the shaped hole. This paper represents the first effort to comprehensively evaluate the surface quantities behind BDSIC film cooling concept using both PSP and TSP techniques.

Non-Adiabatic Surface Effects on Step-Induced Boundary-Layer Transition

The effect on step-induced boundary-layer transition of surface temperatures different from the adiabatic-wall temperature was investigated for a (quasi-) two-dimensional flow at large Reynolds numbers and at both low and high subsonic Mach numbers. Sharp forward-facing steps were mounted on a flat plate and transition was studied non-intrusively by means of the temperature-sensitive paint technique. The experiments were conducted in the Cryogenic Ludwieg-Tube Gottingen with various streamwise pressure gradients and temperature differences between flow and model surface. A reduction of the ratio between surface and adiabatic-wall temperatures had a favorable influence on step-induced transition up to moderate values of the step Reynolds number and of the step height relative to the boundary-layer displacement thickness, leading to larger transition Reynolds numbers. However, at larger values of the non-dimensional step parameters, the increase in transition Reynolds number for a given reduction in the wall temperature ratio became smaller. Transition was found to be insensitive to changes in the wall temperature ratio for step Reynolds numbers above a certain value. Up to this limiting value, the relation between the relative change in transition location (with respect to its value for a smooth surface) and the non-dimensional step parameter was essentially unaffected by variations in the wall temperature ratio. The present choice of non-dimensional parameters allows the effect of the steps on transition to be isolated from the influence of variations in the other factors, provided that both transition locations on the step and smooth configurations are measured at the same conditions.

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.

Nonadiabatic Surface Effects on Transition Measurements Using Temperature-Sensitive Paints

Tests were conducted at the Cryogenic Ludwieg-Tube Göttingen 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 Göttingen 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 shown that a nonadiabatic model surface can strongly influence the boundary-layer transition location.

Fast-response temperature-sensitive-paint measurements on a hypersonic transition cone

Experiments are performed using a fast-response temperature-sensitive-paint (TSP) technique to measure the heat-flux distribution on a slender cone in a hypersonic shock tunnel under both laminar and transitional conditions. The millisecond-order test duration together with the self-luminosity of shock layers place stringent conditions on the choice of TSP luminophore and the TSP-layer thickness that can be employed. The luminosity and dimming from particulates in the free-stream cause additional problems in interpreting the obtained intensity profiles. Nevertheless, favorable agreement with thermocouple-based measurements show that it is possible to derive quantitatively accurate heat-flux distributions with the TSP technique for temperature rises of up to approximately 40 K above room temperature. The technique accuracy is adversely affected at higher temperatures, which is thought to result from non-constant thermal properties of the insulating base layer. At high unit Reynolds number conditions, time-resolved heat-flux distributions show large-scale unsteadiness in the boundary-layer transition location and reveal transient streamwise streaks developing in the transitional region.

Qualification of the ARA TWT for laminar flow testing

AbstractThe current drive towards reducing the environmental impact of aircraft necessitates the ability to evaluate techniques for promoting natural laminar flow in a large scale wind tunnel facility. A test was undertaken on the M2355 variable sweep model to obtain temperature sensitive paint (TSP) and hot-film data from which the transition locations at a range of sweep angles and flow conditions could be identified. The TSP technique has been shown to be a reliable method for determining transition on suitably treated wind tunnel models. Pressure data were also acquired and interpolated to provide the input to the laminar boundary layer code, BL2D, the output from which was used in the linear stability analysis code, CoDS, to calculate the N-factor for the ARA TWT (Transonic Wind Tunnel) facility. Two sets of N-factors were calculated, firstly using incompressible analysis with stationary crossflow and secondly using compressible analysis with travelling crossflow. In both analyses the Tollmien-Schlichting and crossflow cases were calculated together, rather than separating the cases before running the analysis. The resulting N-factors indicate a degree of scatter typical for experimental data. The N-factor based on incompressible theory for crossflow was found to be approximately 7 and for Tollmien-Schlichting (T-S), approximately 11. The results of the wind tunnel test and the analysis carried out are considered to be the first steps towards establishing a methodology for performance testing, in atmospheric tunnels such as the TWT, for aircraft designed to have significant regions of laminar flow. The project has also provided a body of experimental test data which will be valuable for future research into development and validation of laminar flow methods.

The application of temperature-sensitive paints for surface and fluid temperature measurements in both thermal developing and fully developed regions of a microchannel

This work presents the experimental analysis of heat transfer in a straight polydimethylsiloxane microchannel with cross-sectional width/depth ratio of 8.47 using the temperature-sensitive paint (TSP) technique. The TSP technique is capable of acquiring temperature profiles for both the surface and the fluid with a detailed resolution of 144 µm per pixel through the microchannel under the constant wall temperature condition. The acquired temperature data have been analyzed to study the heat transfer and Nusselt numbers in both thermal developing and fully developed regions. The estimation of thermal entrance length from the experimental results shows good agreement with the empirical equation of the parallel-plate system, while the Nusselt numbers in the fully developed region deviate. This deviation is attributed to the small scale of the channel, which amplifies the effects of the electric double layer and the surface boundary condition. These results demonstrate the great potential of the TSP technique in providing detailed and valuable information for heat transfer investigation inside microdevices.

물성치 적용 기법에 따른 하이브리드 풍력 블레이드 동적특성 해석에 관한 연구

In this paper, the heat transfer coefficient measurement techniques using TSP(temperature sensitive paint) were introduced and the results of a comparative study on the heat transfer coefficient measurement by steady state and transient TSP techniques were discussed. The distributions of heat transfer coefficient by a single 60° inclined impingement jet on a flat surface were measured by both techniques. Tested Reynolds number based on the jet diameter (d) was 30,000 and the distance between jet exit and target plate (L) was fixed at 10d. Results showed that the measured Nusselt number by both techniques indicated significant difference except near the center of impingement jet. Also, the heat transfer coefficients measured by the transient TSP technique were affected by the reference temperature of the jet. Based on the measured data, characteristics of both TSP techniques were analyzed and suggestions for applying them were also given.

Investigation of the double ramp in hypersonic flow using luminescent measurement systems

Compression ramp flows in supersonic and hypersonic environments present unique flow patterns for shock wave-boundary layer interaction studies. They also represent the generic geometry of two-dimensional inlets and deflected control surfaces for re-entry vehicles. Therefore, a detailed knowledge of the flow behaviour created by such geometries is critical for optimum design. The flow is made more complicated due to the presence of separation regions and streamwise Görtler vortices. The objective of the current research is to study the behaviour and characteristics of the flow over the double ramp model placed in hypersonic flow at freestream Mach number of 5. Three different incidence angles of 0°, −2°, and −4° are studied using colour Schlieren and luminescent paints consisting of anodized aluminium pressure-sensitive paint (AA-PSP) and the temperature-sensitive paint (TSP) technique. The colour Schlieren provides description of the external flow while the global surface pressure and temperature distribution is obtained through the AA-PSP and TSP methods. The TSP technique also proves that it is very effective in identifying the location and properties of the Görtler vortices; revealing the effect of incidence on the magnitude and pattern of Görtler vortices formed.

경사 충돌 제트 열전달 실험에서 정상 상태와 천이 TSP 기법의 비교 연구

In this paper, the heat transfer coefficient measurement techniques using TSP(temperature sensitive paint) were introduced and the results of a comparative study on the heat transfer coefficient measurement by steady state and transient TSP techniques were discussed. The distributions of heat transfer coefficient by a single 60° inclined impingement jet on a flat surface were measured by both techniques. Tested Reynolds number based on the jet diameter (d) was 30,000 and the distance between jet exit and target plate (L) was fixed at 10d. Results showed that the measured Nusselt number by both techniques indicated significant difference except near the center of impingement jet. Also, the heat transfer coefficients measured by the transient TSP technique were affected by the reference temperature of the jet. Based on the measured data, characteristics of both TSP techniques were analyzed and suggestions for applying them were also given.

Aerodynamic and Endwall Film-Cooling Investigations of a Gas Turbine Nozzle Guide Vane Applying Temperature-Sensitive Paint

Abstract Endwall film-cooling investigations are conducted with a single row of fan-shaped holes in a low-speed, six-bladed linear cascade. The incidence of the inlet flow was changed between −5 deg and 40 deg to achieve higher loading conditions, which results in an intensification of the secondary flow and enhanced interaction with the injected coolant. The investigated profile is based on a near-hub section of the nozzle guide vane of a highly loaded gas turbine. The aerodynamic performance was investigated using pneumatic probes. The film-cooling effectiveness distribution is determined using the temperature-sensitive paint technique. Carbon dioxide was used as coolant to provide elevated density ratios of about 1.4. Although low thermal conductivity material is used for the endwall test plate, the measured temperature fields show influences of 3D-heat conduction inside the test plate. To measure film effectiveness and the heat transfer separately, an adiabatic test surface is needed. Therefore, the effects of heat conduction are modeled using the finite-element-method. With the resulting convective heat flux pattern derived from the computations, the endwall film-cooling measurements are corrected. Furthermore, this approach is applied to evaluate the heat loss inside the holes and the film discharge temperature at the hole exit.