Numerical Investigation of Flow and Heat Transfer over a Shallow Cavity: Effect of Cavity Height Ratio

Flow over shallow cavities is used to model the flow field and heat transfer in a solar collector and a variety of engineering applications. Many studies have been conducted to demonstrate the effect of cavity aspect ratio (AR), but very few studies have been carried out to investigate the effect of cavity height ratio (HR) on shallow cavity flow behavior. In this paper, flow field structure and heat transfer within the 3-D shallow cavity are obtained numerically for two height ratio categories: HR = 0.0, 0.25, 0.5, 0.75, and 1.0 and HR = 1.25, 1.5, 1.75, 2.0, 2.25, and 2.5. The governing equations, continuity, momentum, and energy are solved numerically and using the standard (K-ε) turbulence model. ANSYS FLUENT 14 CFD code is used to perform the numerical simulation based on the finite volume method. In this study, the cavity aspect ratio, AR = 5.0, and Reynolds number, Re = 3 × 105, parameters are fixed. The cavity’s bottom wall is heated with a constant and uniform heat flux (q = 740 W/m2), while the other walls are assumed to be adiabatic. For the current Reynolds number and cavity geometry, a single vortex structure (recirculation region) is formed and occupies most of the cavity volume. The shape and location of the vortex differ according to the height ratio. A reverse velocity profile across the recirculation region near the cavity’s bottom wall is shown at all cavity height ratios. Streamlines and temperature contours on the plane of symmetry and cavity bottom wall are displayed. Local static pressure coefficient and Nusselt number profiles are obtained along the cavity’s bottom wall, and the average Nusselt number for various height ratios is established. The cavity height ratio (HR) is an important geometry parameter in shallow cavities, and it plays a significant role in the cavity flow behavior and heat transfer characteristics. The results indicate interesting flow dynamics based on height ratio (HR), which includes a minimal value in average Nusselt number for HR ≈ 1.75 and spatial transitions in local Nusselt number distribution along the bottom wall for different HRs.

Experimental Investigation of Rossiter Modes for an Open Box Cavity With Adjustable Depth

Resonance in aerospace is a phenomenon that engineers have been trying to predict and avoid for a long time. Acoustic resonance is only a part in this field. When it was previously studied, it was mostly in connection with long slender gaps at the fuselage of aircrafts. Lately it has become a focus in the development of highly efficient aero engines. Bleed systems in the compressor part of engines are needed but not easy to place aerodynamically. Additionally, these bleed systems have complex geometries. These geometries coupled with the operational range of modern aircraft from low to high subsonic Mach numbers can create unwanted acoustic resonances. This paper is part of project study of these resonances. Here the bleed geometry is simplified to an open box cavity that is studied experimentally in order to measure its acoustic behavior in low to high subsonic flow. The experimental data is compared to theoretical prediction models to create a baseline for future studies. The results show a good agreement between Rossiter prediction and experiments for a shallow cavity of L/D = 4. Deeper cavities with a length to depth ratio of one and 0.5 represent more organ pipe resonance phenomena. This is especially governed by the geometry of the cavity itself and the height of the test section. All cavities experience a shift in modes depending on the operating point. This mode shift pattern is similar for deeper cavities. However, the operating range can be divided into four sections in which a mode shift occurs for all cavities.

Aerodynamics and motor control of ultrasonic vocalizations for social communication in mice and rats

Rodent ultrasonic vocalizations (USVs) are crucial to their social communication and a widely used translational tool for linking gene mutations to behavior. To maximize the causal interpretation of experimental treatments, we need to understand how neural control affects USV production. However, both the aerodynamics of USV production and its neural control remain poorly understood. Here we test three intralaryngeal whistle mechanisms - the wall and alar edge impingement, and shallow cavity tone - by combining in vitro larynx physiology and individual-based 3D airway reconstructions with fluid dynamics simulations. Our results show that in the mouse and rat larynx USVs are produced by a glottal jet impinging on the thyroid inner wall. Furthermore, we implemented an empirically based motor control model that predicts motor gesture trajectories of USV call types. Our work provides a quantitative neuromechanical framework to evaluate the contributions of brain and body in shaping USVs, and a first step in linking descending motor control to USV production.

Study on acoustic and flow-induced noise characteristics of L-shaped duct with a shallow cavity

An aerodynamic sound generated by a flow inside a duct is one of the noise pro- blems. Flows in ducts with uneven surfaces such as grooves or cavities can be seen in various industrial devices and industrial products such as air-conditioning equipment in various plants or piping products. In this article, we have performed experiments and simulations to clarify acoustic and flow-induced sound characteris- tics of L-shaped duct with a shallow cavity installed. The experiments and simula- tions were performed under several inflow velocity conditions. The results show that the characteristics of the flow-induced sound in the duct are strongly affected by the acoustic characteristics of the duct interior sound field and the location of the shallow cavity. Especially, it was found that the acoustic characteristics were af- fected by the location of the shallow cavity in the frequency range between 1000 Hz and 1700 Hz.

Mixed Convection in Lid-Driven “T” Shallow Cavity Heated From Bottom and Filled by Two Immiscible Fluids of Air and Al2O3-Water Nanofluid

This work present numerical simulation results of mixed convection in lid-driven “T” shallow cavity, filled by two immiscible fluids layers of air and Al2O3-water nanofluid. Mixed convection condition is created by the upper wall movement and temperature difference between the alveolus bottom and upper wall. Hydrodynamic and thermal characteristics of the flow have been predicted by solving the Navier- Stokes and energy equation using finite volume method. Coupling between two fluids layers are achieved using continuity of temperature and velocity at the interface air-nanofluid. Nano-particle volume fraction effect and geometrical shape of alveolus sidewalls (plane shape, concave shape and convex shape) have been chosen as discussed parameters. Analysis of obtained results shows that the heat transfer rate decreased with increasing volume fraction of solid inside the nanofluid layer. In addition, geometrical shape of alveolus sidewalls has a poor effect on flow structure and isotherms distribution in the physical domain.

EVALUATION OF FLAT SHALLOW CAVITY SOLAR COLLECTOR INSERTED WITH POROUS LAYER

The evaluation of flat shallow cavity solar collector inserted with porous substrate was investigated experimentally and numerically. The aim of this work is to improve the thermal performance of flat plate solar collectors using enhanced heat transfer technique. Porous media were made of multilayer of aluminum mesh to form a porous layer of thickness 25 mm inserted under the absorber plate with porosity of 0.9 and permeability of 84.87. The solar collector was installed in Baghdad south facing at a fixed tilt angle (45°). Three types of solar collector have been designed and constructed namely solar collector made of shallow enclosure (model I), solar collector made of shallow enclosure inserted partially with porous layer (model II) and solar collector with channels of corrugated channels inserted partially with porous layer (model III). The results of parametric study of model III in case of continuous operating showed that the maximum average water temperature difference of water between collector outlet and inlet exceeds (7.21°C) and the maximum outlet temperature exceeds (50°C) at solar noon for (November, and December 2013). The thermal efficiency for collector model III was ranged from 47.52% to 52.2%, while that for model I was ranged (33.5% to 42.3%) under the same environmental conditions.