Data on distribution of heat transfer coefficient and profiles of velocity and turbulent characteristics behind a rib in pulsating flows

The paper presents experimental data on heat transfer and kinematic structure of steady and pulsating flows behind a rib. Several forcing frequencies and one non-dimensional amplitude of pulsation are considered. Distributions of heat transfer coefficient were obtained in the separation region. Optical measurements yielded the profiles of velocity and turbulent characteristics of flow at representative coordinates of the separation region.



.

Effect of flow and humidity on indoor deposition of particulate matter

The removal of particulate matter (PM) is an important issue in public health and the global atmospheric environment. Various PM removal methods have been suggested to effectively remove PM particles. However, the effects of various factors on PM deposition are not completely clear. We quantitatively investigated the effects of flow and humidity difference in a closed chamber on PM deposition. To elucidate the parameters affecting the deposition of PM particles, PM removal efficiency and deposition constant were examined at different flow rates, flow directions, and relative humidity (RH) inside the closed system. The highest PM deposition rate was achieved under humid condition with the upward direction flow at a fan speed of RPM = 150. Mean velocity fields inside the test chamber were obtained by a particle image velocimetry (PIV) technique to quantitatively examine the effect of flow conditions on the PM deposition. The flow structure and RH inside the closed chamber have significant influence on PM deposition.

Physical investigation of the counterjet dynamics during the bubble rebound

The objective of this paper is to investigate the counterjet dynamics generated during the bubble rebound stage near a rigid boundary via both experimental and numerical methods. In the experiments, the temporal evolution of the bubble shapes and the formation of the counterjet are recorded by the high-speed camera. The results are presented for a single bubble generated near different normalized standoff distances γ = L/R_m from 0.5 to 3, where L is the distance between bubble center and boundary, and R_m is the maximum radius of bubble. In order to account for the generation mechanism of counterjet, a 3D weakly compressible model with reformulated mass conservation equation is proposed to predict the transient process of the single bubble patterns and its surrounding flow structure, including the velocity and pressure dynamics and the pressure waves around the bubbles. The results show that the counterjet, the fluid structure opposite to the high-speed jet in the propagation direction, forms during the rebound stage when 1 < γ < 3, and the maximum height of the counterjet increases first and then decreases with the increase of γ. Furthermore, the numerical results show that the generation of counterjet is related to the shock wave induced by bubble collapse. The tension wave causes a low-pressure region at the top of the stagnation ring, which is easy to generate the cavitation bubble. And those cavitation bubbles move upwards along the flow streaming generated inside the stagnation ring, which results in the counterjet.

CFD analysis of the flow structure in a monkey upper airway validated by PIV experiments

Inhalation exposure to airborne contaminants has adverse effects on humans; however, related research is typically conducted using in vivo/in vitro tests on animals. Extrapolating the test results is complicated by anatomical and physiological differences between animals and humans and a lack of understanding of the transport mechanism inside their respective respiratory tracts. This study determined the detailed air-flow structure in the upper airway of a monkey. A steady computational fluid dynamics simulation, which was validated by previous particle image velocimetry measurements, was adopted for flow rates of 4 L/min and 10 L/min to analyze the flow structure from the nasal/oral cavities to the trachea region in a monkey airway model. The low Reynolds number type k-ε model provided a reasonably accurate prediction of the airflow in a monkey upper airway. Furthermore, it was confirmed that large velocity gradients were generated in the nasal vestibule and larynx regions, as well as increased turbulent air kinetic energy and wall sheer stress.

Role of intra-ventricular vortex in left ventricular ejection elucidated by echo-dynamography

PURPOSE

From the correlation between the blood flow dynamics and wall dynamics in the left ventriocle (LV) analyzed using echo-dynamography, the ejection mechanisms and role of the intra-ventricular vortex in the LV were elucidated in detail during the pre-ejection transitional period (pre-ETP), the very short period preceding LV ejection.

METHODS

The study included 10 healthy volunteers. Flow structure was analyzed using echo-dynamography, and LV wall dynamics were measured using both high-frame-rate two-dimensional echocardiography and a phase difference tracking method we developed.

RESULTS

A large accelerated vortex occurred at the central basal area of the LV during this period. The main flow axis velocity line of the LV showed a linearly increasing pattern. The slope of the velocity pattern reflected the deformity of the flow route induced by LV contraction during the pre-ETP. The centrifugal force of the vortex at its junction with the main outflow created a stepwise increase of about 50% of the ejection velocity.

CONCLUSION

Ejection of blood from the LV was accomplished by the extruding action of the ventricular wall and the centrifugal force of the accelerated vortex during this period. During ejection, acceralated outflow was considered to create a spiral flow in the aorta with help from the spherical structure of the Valsalva sinus.