Application of particle image velocimetry measurement techniques to study turbulence characteristics of oscillatory flows around parallel-plate structures in thermoacoustic devices

International Journal of Thermal Sciences

2010

Section: Piv Systemmentioning

confidence: 94%

Application of laser-based instrumentation for measurement of time-resolved temperature and velocity fields in the thermoacoustic system

Shi

International Journal of Thermal Sciences

2010

“…The matching of the experimental data improves if heat transport from the couple of HXs to the surrounding environment (hot and cold ducts) is considered. These heat losses are most likely caused by the entrance/exit effects localized at the resonator-HX cross section interfaces which are responsible of complex non-linear temperature and flow patterns (strong vortex flows and turbulence generation effects [16,17]). Although the simplified model proposed to account for this effect doesn't constitute at this stage a predictive algorithm for quantitative estimations, it provides some evidence that this kind of phenomena could have a non-negligible influence on the value of the heat transfer coefficients at the gas side of the HXs (especially at the hot HX).…”

Section: Figure 7 the Time-averaged Transverse Heat Flux Density At mentioning

confidence: 99%

Heat transfer processes in parallel-plate heat exchangers of thermoacoustic devices – numerical and experimental approaches

Applied Thermal Engineering

Piccolo

2012

This paper addresses the issues of heat transfer in oscillatory flow conditions, which are typically found in thermoacoustic devices. The analysis presented concerns processes taking place in the individual "channels" of the parallel-plate heat exchangers (HX), and is a mixture of experimental and numerical approaches. In the experimental part, the paper describes the design of experimental apparatus to study the thermal-fluid processes controlling heat transfer in thermoacoustic heat exchangers on the micro-scale of the individual channels. Planar Laser Induced The comparisons between the experimental and numerical results in terms of temperature and heat transfer distributions suggest that the optimal performance of heat exchangers can be achieved when the gas displacement amplitude is close to the length of hot and cold heat exchanger. Heat transfer coefficients from the gas-side can be predicted with a confidence of about 40% at moderate acoustic Reynolds numbers.

“…The geometry with W = 5.6 matches the experimental setup used in [1] and is therefore adopted as an example to illustrate the instabilities at various spanwise wavenumbers and Reynolds numbers, as presented in Fig. 5.…”

Section: Modal Stability Analysesmentioning

confidence: 99%

“…It is also noted that the two-dimensional mode (β = 0) is always the most unstable one for a given Reynolds number and therefore the following studies focus on two-dimensional instabilities. [1,5,17]. From the growth rate of the most unstable mode presented in Fig.…”

Section: Modal Stability Analysesmentioning

confidence: 99%

See 1 more Smart Citation

Modal and non-modal stabilities of flow around a stack of plates

Theobald

Mao

European Journal of Mechanics - B/Fluids

et al. 2015

a b s t r a c tModal and non-modal stabilities of flow around a stack of flat plates are investigated by means of asymptotic stability and transient growth analyses respectively. It is observed that over the parameters considered, both the base flow and the stabilities vary as a function of ReW 2 /(W − 1) 2 , i.e. the product of the Reynolds number and the square of the expansion ratio of the stack. The most unstable modes are found to be located downstream of the recirculation bubble while the global optimal initial perturbations (resulting in maximum energy growth over the entire domain) and the weighted optimal initial perturbations (resulting in maximum energy growth in the close downstream region of the stack) concentrate around the stack end owing to the Orr mechanism. In direct numerical simulations (DNS) of the base flow initially perturbed by the modes, it is noticed that the weighted optimal initial perturbation induces periodic vortex shedding downstream of the stack much faster than the most unstable mode. This observation suggests that the widely reported vortex shedding in flow around a stack of plates, e.g. in thermoacoustic devices, is associated with perturbations around the stack end.