Half Of Duct Research Articles

Quantitative flow diagnostics of shock trains by rainbow schlieren deflectometry

AbstractA new measurement technique to reconstruct the density field of the shock-wave/boundary-layer interaction (SWBLI) in a confined duct is proposed. With this technique, it is possible to quantitatively capture in detail the structures of the density field both in the regions of the shock-systems in the central core and boundary-layer flows near the duct wall concurrently. The novel feature of the proposed technique is to make use of the schlieren images with the rainbow filters of the vertical and horizontal cutoff settings and then to reconstruct the two-dimensional density field integrated over the line-of-sight direction using the corresponding filter calibration curves. The proposed technique is applied for the first time to a shock train in a constant-area straight duct under the upstream condition of the shock train: the freestream Mach number is 1.42, the incoming boundary layer thickness normalised by the duct half height is 0.175, and the corresponding unit Reynolds number $Re/m$ is $2.99 \times 10^7$ m-1. The calculated isopycnic field depicts the streamwise and transverse density variations inside the shock train, the mixing region after the shock train, and the boundary-layer of the interaction region. This technique is shown to be capable of identifying the locations of shocks in a shock train more precisely than a conventional approach measuring the static pressure distribution along the duct wall. In addition, various quantitative visual representations such as a shadowgraphy and a bright-field schlieren can be extracted from the density field acquired by the present approach, and the spatial evolution of the shape and strength of each shock constituting the shock train as well as the boundary layer flow properties can be quantitatively clarified.

Mathematical Modelling of Triple Diffusion in Natural Convection Flow in a Vertical Duct with Robin Boundary Conditions, Viscous Heating, and Chemical Reaction Effects

The triple-diffusive convective flow (thermal diffusion and dual species diffusion) in a viscous fluid flowing within a vertical duct is investigated subject to Robin boundary conditions at the duct walls. Viscous heating and homogenous chemical reaction effects are included. The mass transfer (solutal) buoyancy effects due to concentration gradients of the dispersed components are taken into account using the Boussinesq approximation. Symmetric and asymmetric wall conditions for the temperature are taken into account. The conservation equations are rendered into dimensionless form via suitable transformations and the emerging ordinary differential equations feature a number of dimensionless parameters including thermal Grashof number, two solutal Grashof numbers (one for each of the diffusing components i.e. species 1 and species 2), left and right duct wall thermal Biot numbers, species 1 and species 2 chemical reaction parameters, Brinkman number and temperature difference ratio.These coupled and nonlinear dimensionless conservation equations are solved numerically using theRunge-Kutta shooting method. The solutions obtained numerically are validated with approximate analytical solutions obtained via a regular perturbation method which are valid for small values of Brinkman number.The impact of selected parameters on velocity, temperature and dual species concentration distributions is visualized graphically. Furthermore, the variation of skin friction and Nusselt number with these parameters is also tabulated. The solutions obtained numerically and analytically are found to be equal in the absence of viscous dissipation. However, the deviation is magnified with large values of Brinkman number. In the absence of chemical reaction, the results concur with the earlier computations of Zanchini (1998). Increasing second species solutal Grashof number is observed to decelerate the flow in the left duct half space, to accelerate the flow in the right duct half space and consistently reduce temperatures across the entire duct width. With increasing species 1 chemical reaction parameter the concentration magnitudes are elevated in the left duct half space whereas they are depressed in the right duct half space. A similar response is computed for the influence of species 2 reaction parameter on the concentration profile. Temperatures are strongly enhanced across the duct width with increasing Brinkman number and are symmetric in nature about the channel centerline for the symmetric Biot number case (equal thermal Biot numbers at the left and right walls). These profiles are morphed for the asymmetric Biot number case (equal thermal Biot numbers at the left and right walls). Temperatures descend from the left wall to the right wall, although they are still enhanced with increasing Brinkman number. The simulations are relevant to geochemical transport phenomena, industrial materials processing and thermal duct design.

Effect of Inner and Outer Horizontal wall Heating on Porous Duct

Heat Transfer analysis in a square porous annulus is conducted with respect to heating of 4 inner walls along with outer horizontal walls and cooling of outer vertical walls cooling. Darcy law along with Boussinesq approximation is applicable. Two phases of porous medium such as solid and fluid phase are in thermal equilibrium. The governing equations are approximated using Galerkin method and converted into algebraic equation using finite element method. The fluid is found to flow in vertical cells along left and right half of duct. The top section of duct is found to have minimum thermal energy as compared to other parts of duct.

Sound Propagation in a Duct with Wall Corrugations Having Square-Wave Profiles

Acoustic wave propagation in ducts with rigid walls having square-wave wall corrugations is considered in the context of a perturbation formulation. Using the ratio of wall corrugation amplitude to the mean duct half width, a small parameter is defined and a two levels of approximations are obtained. The first-order solution produces an analytical description of the pressure field inside the duct. The second-order solution yields an analytical estimate of the phase speed of waves transmitting through the duct. The effect of wall corrugation density on acoustic impedance and wave speeds is highlighted. The analysis reveals that waves propagating in a duct with square-wave wall corrugation are slower than waves propagating in a duct with sinusoidal wave corrugation having the same corrugation wavelength.

Reynolds number effect on turbulent secondary flow in a duct

Numerical simulations of fully-developed turbulent flow through a straight square duct at three Reynolds numbers of 190, 300, and 550 based on the friction velocity averaged over the duct perimeter and duct half width are reported. The effect of Reynolds number on the mean and turbulence statistics and secondary flow is investigated. The mean streamwise-velocity profiles along the wall bisector are found to obey a logarithmic scaling when they are normalized by the friction velocity at the mid-wall. Magnitudes and spatial distributions of the peak production and diffusion terms in the mean streamwise-vorticity equation normalized by the wall units are found to be unaffected by the Reynolds-number variation when they are considered in wall-unit coordinates.

The effect of endoscopic sphincterotomy on the motility of the gallbladder and sphincter of Oddi in patients with acalculous biliary pain syndrome

Sphincter of Oddi dysfunction usually occurs after cholecystectomy, but it can sometimes be detected in patients with intact gallbladder too. The diagnostic value of the non-invasive functional tests is not established in this group of patients and the effects of sphincterotomy on transpapillary bile outflow and gallbladder motility are unknown. The aim of this study was to determine the effect of endoscopic sphincterotomy on the gallbladder ejection fraction, transpapillary bile outflow and the clinical symptoms of patients with acalculous biliary pain syndrome. 36 patients with acalculous biliary pain syndrome underwent quantitative hepatobiliary scintigraphy, and all of them had decreased cholecytokinin-induced gallbladder ejection fraction. The endoscopic manometry of the sphincter of Oddi showed abnormal sphincter function in 26 patients who were enrolled the study. Before and after endoscopic sphincterotomy all patients had ultrasonographic measurement of cholecystokinin-induced gallbladder ejection fraction with and without nitroglycerin pretreatment and scintigraphy was repeated as well. The effects of sphincterotomy on gallbladder ejection fraction and transpapillary biliary outflow were evaluated. In addition, changes in biliary pain score with a previously validated questionnaire were also determined. All 26 patients had decreased gallbladder ejection fraction before sphincterotomy measured with scintigraphy (19+18%) and ultrasound (16+9.7%), which was improved after nitroglycerin pretreatment (48.2+17%; p<0.005). Detected with both methods, the ejection fraction was in the normal range after sphincterotomy (52+37% and 40.8+16.5%), but nitroglycerin pretreatment failed to produce further improvement (48.67+22.2%, NS). Based on scintigraphic examination sphincterotomy significantly improved transpapillary biliary outflow (common bile duct half time 63±33 min vs. 37±17 min; p<0.05). According to results obtained from questionneries, 22 of the 26 patients gave an account of significant symptom improvement after sphincterotomy. Endoscopic sphincterotomy improves cholecystokinin-induced gallbladder ejection fraction, transpapillary biliary outflow as well as biliary symptoms in patients with acalculous biliary pain syndrome and sphincter of Oddi dysfunction. Cholecystokinin-induced gallbladder ejection fraction with nitroglycerin pretreatment, measured with ultrasonography can be useful to select a subgroup of patients who can benefit from sphincterotomy.

Influence of duct geometry on the performance of Darrieus hydroturbine

Computational study is carried out to develop a new duct with the purpose of improving the performance of a straight-bladed Darrieus hydroturbine. Though Darrieus turbine is very simple to construct, it has some disadvantages when compared to axial turbines. These are a lower power coefficient and a variation in the torque produced within the cycle leading to periodic loading on the components of the turbine. The main objective of the present study is to retain the simple design and fabrication procedure of Darrieus turbine while reducing the disadvantages. In this study, a new duct is developed, for a given turbine design, that reduces the variation in torque over a cycle by appropriately directing the flow upstream and downstream the turbine while increasing power conversion. At the operating point, which is at a tip-speed ratio of 2, use of a duct reduces the torque ripple by a factor of 4.15 and the power coefficient( C p )is increased to 0.63 from 0.40. By choosing the position of the turbine in the duct appropriately, it is shown that the torque ripple may be reduced by a factor of 6.37, at the expense of the power coefficient. And, a maximum C p = 0.644 is observed when the turbine center coincided with the throat of the duct. Similarly, the effect of varying other parameters such as the convergence angle of the duct and its external shape on the performance of the turbine are studied through numerical simulation. It is seen that there exists an optimum value in each case. While varying the convergence angle of the duct it is observed that the maximum power coefficient and lowest torque ripple are obtained at the same value of duct half angle, equal to 27°. The dependence of the power coefficient and torque ripple on duct convergence angle is weak. The duct with straight external shape is observed to have best performance with a peak power coefficient of 0.72, while the convex external shape has a peak of only 0.51. The external shape is observed to have a negligible effect of the torque ripple factor. Significance of the emerging trends of parameters are discussed. ► Numerical simulation of the effect of duct on the performance of Darrieus turbine. ► Torque ripple reduces by 4.15 and power conversion factor increases to 0.63 from 0.4. ► Lowest torque ripple is 0.2 when the turbine centre is 0.4 m upstream of the throat. ► Power conversion is the maximum when the turbine is at the throat. ► Duct with straight external shape has a peak power coefficient of 0.72.

B207 断面積一定のダクトにおけるショックトレーンの形状に関する可視化研究

Flow visualization using a color schlieren system and wall pressure measurements have been performed to elucidate the interaction of a weak normal shock wave and a boundary layer in a constant-area duct. The freestream Mach number just upstream of the shock is about 1.3 and the flow confinement given as the ratio of the boundary layer thickness to the duct half height ranges from 0 to about 6%. The schlieren visualization shows that with increasing flow confinement, single normal shock gradually changes into a shock train consisted of four shocks.

Multiple normal shock wave/turbulent boundary-layer interactions

A multiple normal shock/turbulent boundary-layer interaction in a rectangular duct has been investigated experimentally using a two-component laser Doppler velocimeter (LDV). Just upstream of the normal shock system the Mach number was 1.61, the unit Reynolds number was 30 x 106 m ', and the confinement level as characterized by the ratio of the boundary-layer thickness to the duct half height was 0.32. The results presented here identify the fluid dynamic mechanisms involved in the reacceleration process following each shock in the multiple shock system. Two distinct expansion processes occur following each shock in the system: acceleration through a supersonic expansion fan originating near the wall and acceleration through an aerodynamic converging-diverging nozzle in the core flow.

Pharmacological investigation of the venoms of the marine snails Conus textile and Conus geographus

Phrenic nerve-diaphragm preparations and isolated skeletal muscles were exposed to two Conus venoms. Rats and mice were injected intraperitoneally. Anaesthetized rats and guinea-pigs were injected intravenously, the sciatic nerve being exposed and stimulated to give a foot twitch. Paralysis of diaphragm and other isolated muscles was observed only after administration of venom from the posterior half (approximately) of the venom duct of C. geographus. The anterior half of the duct of C. geographus and the whole of the duct of C. textile failed to yield venom capable of paralyzing isolated muscles or of causing symptoms in rats and mice on intraperitoneal injection. Venom active on isolated skeletal muscle caused respiratory failure in anaesthetized animals, the foot twitch response to sciatic nerve stimulation being simultaneously abolished. Recovery in both aspects usually occurred after artificial respiration. Active venom paralyzed skeletal muscle directly without prior neuromuscular blockade. However, there was enhancement of the effect of liminal doses of tubocurarine on the neuromuscular junction, and tubocurarine enhanced the muscle paralysis produced by small doses of venom. Eserine was without effect on the muscle paralysis.