An Experimental Investigation of Shock-Induced Panel Flutter Using Simultaneous PIV and DIC

The vibration of panel structural elements immersed in a supersonic flow is a poorly understood fluid-structure interaction (FSI) that can affect the performance and structural integrity of supersonic aircraft and spacecraft systems. These adverse effects are further amplified when a shock-wave/boundary-layer interaction (SWBLI) is formed over the panel. A better understanding of this phenomenon—referred to as shock-induced panel flutter—is therefore crucial for the design of future high-speed vehicles.An experimental method is developed to study shock-induced panel flutter at Mach 2 using planar particle image velocimetry (PIV) and stereographic digital image correlation (DIC) to obtain simultaneous, full-field structural displacement and flow velocity measurements. High-speed cameras are employed to conduct spectral analyses of the panel’s motion and the low-frequency dynamics of the SWBLI during the interaction. To avoid optical interference between the PIV and DIC systems, an optical isolation system is devised using fluorescent paint, dedicated light sources, and color lens filters. The devised experimental setup is used to study the effects of an impinging oblique shock on the dynamics of a flexible panel during flutter, and the effects on the mean flow separation and interaction length of a SWBLI when a rigid wall is substituted by a compliant plate. The coupling of the panel and SWBLI is also studied, identifying the regions in the flow of maximum correlation between the panel’s motion and the flow velocity fluctuations. The obtained results suggest that the inviscid flow region upstream of the SWBLI may play a significant role in the fluid-structure interaction. In addition, a parametric study is conducted to determine the effects of panel aspect ratio and edge boundary conditions on the three-dimensionality of the panel dynamics. The reported findings serve as a reference for future researchers when designing both experimental and numerical simulations of shock induced panel flutter, particularly if two-dimensional flutter is to be recreated.Aerospace Engineerin

Investigation of the influence of operation conditions on the discharge of PCM ceiling panels

The aim of this study was to determine favorable operation conditions for ceiling panels containing phase change materials (PCM) for cooling applications in office rooms. A recently renovated room in the Technical University of Denmark was used to have realistic boundary conditions. Using TRNSYS 17, the performance of the PCM panels during the cooling season in passive operation, discharge by air, and discharge by water circulation were investigated. A set of simulations were performed during a representative week in the cooling period. The room was simulated with no climatic systems, PCM without active discharge, ventilation during occupied hours only, and PCM with ventilation during occupied hours. Afterwards, two discharge methods were investigated, night ventilation at different flow rates and water circulation in pipes embedded in the panels. A parametric analysis was performed to identify the influence of operation factors in the thermal environment of the room. The parameters studied were the water flow rate, supply water temperature and circulation schedule as well as the conductivity of the PCM. After selecting different operating conditions of the water discharge, simulations were performed from May to October to observe the performance of the selected operation conditions. The results show that the PCM is more effective to provide adequate indoor thermal conditions if it is discharged actively by means of water. The parameters that affect the thermal indoor environment the most are the water circulation schedule, the water supply temperature, and the PCM thermal conductivity. The water flow rate did not have a significant influence. The study shows the importance of selecting an appropriate operation and control strategy for the PCM system. The process used in the study can be potentially used as a procedure for the design of similar climatic systems to determine if active discharge of the PCM is needed and if yes, which discharge method is needed

Energy and thermal comfort performance evaluation of PCM ceiling panels for cooling a renovated office room

The performance of suspended ceiling panels with phase change materials (PCM) for comfort cooling applications in office rooms was studied. The panel consisted of a metal casing, which encapsulates the PCM. Water can circulate through the pipes embedded in the panel to influence the latent energy storage of the material. To evaluate the performance of the PCM panels, a comparison with an all-air system and a thermally active building system (TABS) was made. Using TRNSYS 17, a recently renovated room in the Technical University of Denmark was modelled. The room was simulated during the cooling season with each of the three cooling systems in which the thermal environment and the corresponding energy use were determined. Operative temperature was maintained between 22°C to 27°C at least 90% of the occupied period with each system. Similarities were observed between the PCM and TABS systems. Energy savings of 15% and peak cooling power reduction of 30% compared with the all-air system were observed. This study proved the common claim that PCM ceiling panels and TABS perform similar in terms of the created thermal indoor environment and energy savings, as well in terms of heat removal from the indoor space. Therefore, PCM ceiling panels could be used as an alternative for TABS in renovation projects while providing similar benefits to TABS

Characterization of shock-induced panel flutter with simultaneous use of DIC and PIV

In this experimental study, panel flutter induced by an impinging oblique shockwave is investigated at a freestream Mach number of 2, using the combination of planar particle image velocimetry (PIV) and stereographic digital image correlation (DIC) to obtain simultaneous full-field structural displacement and flow velocity measurements. High-speed cameras are employed to obtain a time-resolved description of the panel motion and the shockwave-boundary layer interaction (SWBLI). In order to prevent interference between the PIV and DIC systems, an optical isolation is implemented using fluorescent paint, dedicated light sources, and camera lens filters. The effect of the panel motion on the SWBLI behavior is assessed, by comparing it with the SWBLI on a rigid wall. The results show that panel oscillations occur with a maximum amplitude of ten times the panel thickness. The dominant frequencies observed in the panel oscillation (424 Hz and 1354 Hz) match the main spectral content of the reflected shockwave position. A further POD analysis of the panel displacement spatial distribution shows that these two frequency contributions are well captured by the first two POD modes, which correspond, respectively, to a first and a third bending mode shape and account for 92% of the total oscillation energy. The fluid-structure coupling is studied by identifying, in the flow, the regions of maximum correlation between the panel displacement and the flow velocity fluctuations. The results obtained prove that the inviscid flow region upstream of the SWBLI is perfectly in phase with the panel oscillation, while the downstream region has a delay of one quarter of the flutter cycle.Aerodynamic