Development of an Infrared Thermography System to Measure Boundary Layer Transition in a Low Speed Wind Tunnel Testing Environment

The use of infrared thermography for boundary layer detection was evaluated for use in the Cal Poly Low Speed Wind Tunnel (LSWT) and recommendations for the successful use of this technique were developed. In cooperation with Joby Aviation, an infinite wing model was designed, manufactured and tested for use in the LSWT. The wing was designed around a custom airfoil profile specific for this project, where the nearly-flat pressure gradient at a zero pitch angle would delay the chordwise onset of boundary layer transition. Steady-state, RANS numerical simulations predicted the onset of transition to occur at 0.75 x/c for the design Reynolds Number condition of 6.25x105. The wing was manufactured from 3D printed aluminum, with a wall thickness of 0.125 inches and a chord length of 13.78 inches. Two central rows of static pressure taps were used, each with 12 functional chordwise locations. The taps were able to generate strong correlation to the numerically predicted pressure coefficient distribution. The use of an infrared camera visualized and confirmed the presence of boundary layer transition at the chordline location anticipated by the early simulations. To do so, the model was pre-heated such that the differential cooling properties of laminar and turbulent flow would generate a clear temperature gradient on the surface correlating to boundary layer transition. Adjustment of the model’s pitch angle demonstrated a change in the onset location of boundary layer transition during the infrared testing. The change of onset location was seen to move forward along the chordline as the aerodynamic angle of attack was increased. Testing with a Preston Tube system allowed for the interpolation of local skin friction coefficient values at each static tap location. Application of both laminar and turbulent empirical assumptions, when compared to numerical expectations, allowed for the qualitative assessment of boundary layer transition onset. Overall, the wing model developed for this research proved capable of producing quality and repetitive results for the experimental goals it was designed to meet. The model will next be used in continued tests which will further explore the use of infrared thermography

Heat dissipation during hovering and forward flight in hummingbirds

Flying animals generate large amounts of heat, which must be dissipated to avoid overheating. In birds, heat dissipation is complicated by feathers, which cover most body surfaces and retard heat loss. To understand how birds manage heat budgets during flight, it is critical to know how heat moves from the skin to the external environment. Hummingbirds are instructive because they fly at speeds from 0 to more than 12ms−1, during which they transit from radiative to convective heat loss. We used infrared thermography and particle image velocimetry to test the effects of flight speed on heat loss from specific body regions in flying calliope hummingbirds (Selasphorus calliope). We measured heat flux in a carcass with and without plumage to test the effectiveness of the insulation layer. In flying hummingbirds, the highest thermal gradients occurred in key heat dissipation areas (HDAs) around the eyes, axial region and feet. Eye and axial surface temperatures were 8◦C or more above air temperature, and remained relatively constant across speeds suggesting physiological regulation of skin surface temperature. During hovering, birds dangled their feet, which enhanced radiative heat loss. In addition, during hovering, near-body induced airflows from the wings were low except around the feet (approx. 2.5ms−1), which probably enhanced convective heat loss. Axial HDA and maximum surface temperature exhibited a shallow U-shaped pattern across speeds, revealing a localized relationship with power production in flight in the HDA closest to the primary flight muscles. We conclude that hummingbirds actively alter routes of heat dissipation as a function of flight speed

Exergy-based Planning and Thermography-based Monitoring for energy efficient buildings - Progress Report (KIT Scientific Reports ; 7632)

Designing and monitoring energy efficiency of buildings is vital since they account for up to 40% of end-use energy. In this study, exergy analysis is investigated as a life cycle design tool to strike a balance between thermodynamic efficiency of energy conversion and economic and environmental costs of construction. Quantitative geo-referenced thermography is proposed for monitoring and quantitative assessment via continued simulation and parameter estimation during the operating phase

GTE laboratories microelectronics research program

Issued as Quarterly progress reports [nos.1-8], and Final report, Project no. E-25-669 (subproject under B-10-628

Advances in structural analysis and process monitoring of thermoplastic composite pipes.

Thermoplastic composite pipes (TCP) in comparison to other pipes have proven beneficial features due to its flexibility which includes being fit for purpose, lightweight and no corrosion. However, during the manufacturing of TCP which involves the consolidation process, certain defects may be induced in it because of certain parameters, and this can affect the performance of the pipe in the long run as the induced defects might lead to in-service defects. Current techniques used in the industry are facing challenges with on-the-spot detection in a continuous manufacturing system. In TCP manufacturing process, the pipe is regularly monitored. When a defect is noticed, the whole process stops, and the appropriate action is taken. However, shutting down the process is costly; hence it is vital to decrease the downtime during manufacturing to the barest minimum. The solutions include optimizing the process for reduction in the manufacturing defects amount and thoroughly understanding the effect of parameters which causes certain defect types in the pipe. This review covers the current state-of-the-art and challenges associated with characterizing the identified manufacturing induced defects in TCP. It discusses and describes all effective consolidation monitoring strategy for early detection of these defects during manufacturing through the application of suitable sensing technology that is compatible with the TCP. It can be deduced that there is a correlation between manufacturing process to the performance of the final part and selection of characterization technique as well as optimizing process parameters

Two dimensional gas temperature measurements of fuel sprays in a high pressure cell

Premixed charge compression ignition (PCCI) is a promising low-emission combustion concept. By partially mixing the fuel, air and exhaust gas before auto-ignition, the soot and NOx emissions are lower than for conventional diesel combustion. However, the fundamental aspects of the mixing process of the fuel spray with the ambient air are still not well understood, especially not in terms of the temperature distribution of the fuel/air mixture. This thesis focuses on the 2D temperature distribution measurement of fuel sprays under conditions relevant to PCCI-mode combustion in heavy-duty Diesel engines. Experiments are performed in the High Pressure Cell (HPC), which simulates engine conditions while providing much better optical accessibility than a real engine. The temperature field which is produced by the pre-combustion technique is also measured, to characterize the ambient condition which the sprays are injected in. Advanced diagnostics are applied to provide detailed information on fuel sprays and the ambient condition, to improve the understanding of the mixing mechanism and its consequences for the combustion process. Chapter 2 describes the pre-combustion technology of the HPC and the modeling of the cooling process. The analytical modeling is based on experimental observations, assuming that turbulent convection is dominating the cooling process. A natural and a forced convection model are used to estimate the thermal boundary layer thickness and the core temperature in the scenarios without and with fan-mixing, respectively. Without fan-mixing the heat transfer rate decays together with the turbulent kinetic energy. If fan mixing is added, a constant turbulent flow is maintained, that is, the turbulent kinetic energy is constant during the cooling process. The modeling results match experimental results very well. In the first scenario, the core temperature is about 5 – 7% higher than the bulk temperature. In the second scenario the difference is 2 – 6%. These results are reasonable when compared with experiments. The model provides a good estimation for the ambient condition during fuel spray measurements. In Chapter 5, Laser Induced Phosphorescence (LIP) is chosen to measure the temperature field of the ambient gas prior to fuel injection. The BAM (BaMgAl10O17:Eu) is chosen as a tracer phosphor for its high signal-to-noise ratio and its capability to survive the pre-combustion. A seeding device to seed the 3 µm solid particles into gaseous flow was designed and implemented, which performed beyond expectation. Particle agglomeration was not observed, probably due to the high shear forces induced. Particle sticking is not a major concern as long as stainless steel tubing is used and Teflon material is avoided. BAM-LIP is excited by a 355 nm YAG laser. Results show that BAM-LIP can be used to measure the temperature field of the residual gas in the HPC below 650 K. The precision of the experiments is better than 30 K at 400 K and 60 K at 650 K. The spatial resolution was estimated to be 3 mm in the plane of the laser sheet and 10 mm along the line of sight, primarily determined by multiple scattering present in the experiments. Temperature field results show that there is a significant temperature gradient in the vertical direction present during the cooling phase in the HPC when the mixing fan is not used. This finding supports the interpretation of the analytical model, which overpredicts the temperature for neglecting the buoyancy effect. However the BAM-LIP method is currently not able to provide 2D temperature distribution prior to fuel injection, due to the lack of signal due to particle falling. Possible improvements have been recommended. In Chapter 3, the physical processes in a fuel spray, as it is injected into stagnant ambient gas, are explained and two phenomenological spray models are compared in their prediction of temperature distribution in a fuel spray. The major difference between the Versaevel and the Valencia model exists in their assumptions for radial profiles of fuel concentration and velocity. The Versaevel model assumes a top-hat profile while the Valencia model assumes a Gaussian profile, which is observed by averaging multiple injections. Both models predict spray penetration very well, however, they differ considerably in their prediction of the temperature distribution. The Valencia model predicts lower central line temperatures than the Versaevel model. Laser Induced Fluorescence (LIF) using 10% toluene as a tracer, as described in Chapter 5, is used as a tool to measure 2D temperatures during and after injection of fuel inside the HPC and an optical engine. The error analysis and evaluation of the toluene LIF method was performed on the HPC, while the calibration was performed in the optical engine. The toluene LIF method is capable of measuring temperatures up to 700 K; above that the signal becomes too weak. The precision of the spray temperature measurements is 4% and the spatial resolution is 1.3 mm. Experimental results from the HPC reveal a hot zone in the fully developed spray. Two camera configurations are compared. An opposite side camera setup seems to be beneficial over a one-side setup because it avoids the dichroic beam splitter requirement, but the precision is lower because of different light paths. The toluene LIF method offers a relatively simple and precise way to measure the 2D temperature distribution in fuel sprays. However, several improvements can be done to improve the absolute accuracy, For example using more sensitive camera and applying flat field correction with a light source of the relevant wavelength. In general, the toluene LIF method is capable of providing 2D temperature information in a fuel spray with 4% precision, which makes it possible to detect the temperature gradients in sprays. The BAM-LIP method could be used in measuring the temperature distribution in a gas-phase environment, where combustible tracers, such as toluene, are not applicable. Both methods might be applied in more applications such as in burners and internal combustion engines

Applicability of correlated digital image correlation and infrared thermography for measuring mesomechanical deformation in foams and auxetics

Cellular materials such as metal foams or auxetic metamaterials are interesting microheterogeneous materials used for lightweight construction and as energy absorbers. Their macroscopic behavior is related to their specific mesoscopic deformation by a strong structure-property-relationship. Digital image correlation and infrared thermography are two methods to visualize and study the local deformation behavior in materials. The present study deals with the full-field thermomechanical analysis of the mesomechanical deformation in Ni/PU hybrid foams and Ni/polymer hybrid auxetic structures performing a correlative digital image correlation and infrared thermography. Instead of comparing and correlating only the primary output variables of both methods, strain and temperature, also strain rates and temperature rates occurring during deformation were compared. These allow for a better correlation and more conclusive results than obtained using only the primary output variables

VISUALIZATION AND CHARACTERIZATION OF ULTRASONIC CAVITATING ATOMIZER AND OTHER AUTOMOTIVE PAINT SPRAYERS USING INFRARED THERMOGRAPHY

The disintegration of a liquid jet emerging from a nozzle has been under investigation for several decades. A direct consequence of the liquid jet disintegration process is droplet formation. The breakup of a liquid jet into discrete droplets can be brought about by the use of a diverse forcing mechanism. Cavitation has been thought to assist the atomization process. Previous experimental studies, however, have dealt with cavitation as a secondary phenomenon assisting the primary atomization mechanism. In this dissertation, the role of the energy created by the collapse of cavitation bubbles, together with the liquid pressure perturbation is explicitly configured as a principal mechanism for the disintegration of the liquid jet. A prototype of an atomizer that uses this concept as a primary atomization mechanism was developed and experimentally tested using water as working fluid. The atomizer fabrication process and the experimental characterization results are presented. The parameters tested include liquid injection pressure, ultrasonic horn tip frequency, and the liquid flow rate. The experimental results obtained demonstrate improvement in the atomization of water. To fully characterize the new atomizer, a novel infrared thermography-based technique for the characterization and visualization of liquid sprays was developed. The technique was tested on the new atomizer and two automotive paint applicators. The technique uses an infrared thermography-based measurement in which a uniformly heated background acts as a thermal radiation source, and an infrared camera as the receiver. The infrared energy emitted by the source in traveling through the spray is attenuated by the presence of the droplets. The infrared intensity is captured by the receiver showing the attenuation in the image as a result of the presence of the spray. The captured thermal image is used to study detailed macroscopic features of the spray flow field and the evolution of the droplets as they are transferred from the applicator to the target surface. In addition, the thermal image is post-processed using theoretical and empirical equations to extract information from which the liquid volume fraction and number density within the spray are estimated

Multi-layer carbon fiber reinforced plastic characterization and reconstruction using eddy current pulsed thermography

Ph. D. Thesis.Carbon fibre composite materials are widely used in high-value, high-profit applications, such as aerospace manufacturing and shipbuilding – due to their low density, high mechanical strength, and flexibility. Existing NDT techniques such as eddy current testing suffers from electrical anisotropy in CFRP (carbon fibre reinforced plastics). Ultrasonic is limited by substantial attenuation of signal caused by the multilayer structure. The eddy current pulsed thermography has previously been applied for composites NDE (non-destructive evaluation)such as impact damage, which has the ability for quick and accurate QNDE(quantitative non-destructive evaluation) inspection but can be challenging for detection and evaluation of sub-surface defects, e.g., delamination and debonding in multiple layer structures. Developing QNDE solutions using eddy current thermography for addressing subsurface defects evaluation in multi-layer and anisotropic CFRP is urgently required. This thesis proposes the application of eddy current pulsed thermography (ECPT) and ECPuCT (eddy current pulse compression thermography) for tackling the challenges of anisotropic properties and the multi-layer structure of CFRP using feature-based and reconstruction-based QNDE and material characterisation. The major merit for eddy current heating CFRP is the volumetric heating nature enabling subsurface defect detectability. Therefore, the thesis proposes the investigation of different ECPT and their features for QNDE of various defects, including delamination and debonding. Based on the proposed systems and QNDE approach, three case studies are implemented for delamination QNDE, debonding QNDE, conductivity estimation and orientation inverse reconstruction using the two different ECPT systems and features, e.g., a pulse compression approach to increase the capability of the current ECPT system, the feature-based QNDE approach for defect detection and quantification, and reconstruction-based approach for conductivity estimation and inversion. The three case studies include 1) investigation of delamination with different depths in terms of delamination location, and depth quantification using K-PCA, proposed temporal feature-crossing point feature and ECPuCT system; 2) investigation of debonding with different electrical and thermal properties in terms of non-uniform heating pattern removal and properties QNDE using PLS approaches, impulse response based feature

Study of a low Re airfoil considering laminar separation bubbles in static and pitching motion

Performance of low Reynolds number (Re) devices is highly dependent on their airfoil design. Small wind turbines that usually work in areas with poor wind resources with a vast application from remote to busy urban regions are no exception. The unsteady flow field around the turbine blade results in an unsteady boundary layer that makes aerodynamics of these turbines complex and interesting. But due to the complexity of unsteady low Reynolds flow, and the small scale of boundary layer flow there are still unanswered questions in this area. Therefore, this study is arranged to fully investigate low Reynolds number boundary layer flow in steady and unsteady flow using small scale experiments. For this goal, three non-intrusive experimental techniques used to study low Re flow behavior over a miniature SD7037 airfoil including surface oil flow visualization (SOFV), IR-Thermography (IT), and particle image velocimetry (PIV) at 14000 < Re < 48000 have been developed and utilized. To model unsteady flow a pitch oscillation about the static stall angle of attack with amplitude 9 was considered. The quality of acquired results from all the experimental methods confirms the possibility of downscaling of low Reynolds flow experiments. Flow parameters such as the separation and reattachment points were quantitatively determined from SOFV and IT. The high-resolution PIV measurements provided an accurate velocity field so that surface pressure distribution and estimation of skin friction coefficient were determined from the velocity fields in both the steady and unsteady flow where due to the scale of the experiment and low magnitude of shear stress other measurement techniques would be intrusive or cannot be used. Estimated surface pressure coefficient (Cp) from PIV data revealed vortical structure effects as low-pressure waves that cannot be captured with coarse resolution methods. Integral boundary layer parameters are calculated in steady and unsteady conditions that provide in-depth information regarding low Re boundary layer flow behavior and laminar separation bubble characteristics. Boundary layer flow and reversed flow under the separated bubble were captured precisely while the Field of View covers the whole airfoil and results were confirmed by acquired data using finer spatial resolution. The measured aerodynamic force shows the effect of the height of the bubble on increasing the drag and the proper orthogonal decomposition method provided more information regarding the time-dependent behavior of vortices