Hemispherical Body Research Articles

Numerical Investigations of Flow Field over Conical, Disc and Flat-Face Spiked-Nose Attached to a Hemisphere Body at Mach 6

Numerical Investigations of Flow Field over Conical, Disc and Flat-Face Spiked-Nose Attached to a Hemisphere Body at Mach 6

Drag Reduction of a Hemispherical Body Adopting Spike at Supersonic Speed

Use of spike on a hemispherical body changes the flow field and hence the aerodynamic drag. Experimental and computational studies have been made to obtain the flow field around a hemispherical body with spikes at a supersonic Mach number of 2. The effect of shape of spike tip and length has been studied. Experiments consisted of shadowgraph flow visualisation and measurement of drag. Computations have been made adopting structured grid and k-ω turbulence model using commercial software Fluent. It is observed that use of a sharp spike itself reduces the drag significantly. However the use of a hemispherical head spike further reduces the drag. Contribution of different components towards drag indicate that the increase in length of a spike do not change the spike contribution. However the flow field on main body is altered which leads to reduction in drag with change in length. Estimated drag generally found to be higher in comparison to measured value, however the trend is almost similar.

Análise tridimensional de elementos finitos de três geometrias implante-abutment cônicos internos

ABSTRACT Objective: The aim of this study was to compare the stress distribution in internal tapered connection implants with different adaptation geometries submitted to oblique load simulation using the Finite Element Analysis (FEA) method. Methods: Three different internal tapered implant-abutment assemblies were modeled by varying only the diameter of the abutment body in the cone region. The dimensions of the implants were 4.0 mm in diameter and 13 mm in length. Oblique loads of 210 N angled 30 degrees to the long axis of the implant were applied to a hemispherical body positioned over the abutments simulating a dental crown. The stress generated by the implant-abutment assembly was analyzed by the FEA method using the von Mises criterion. Results: A higher concentration of stress in the coronal region (collar) and implant body on the opposite side of the load application was shown, as well as in the body region of the abutments and in the screw threads. The cervical region of the implants showed the highest von Mises stress values, the highest values being observed in G3 (1034 MPa), followed by G2 (841 MPa) and G1 (702 MPa). Conclusion: According to the results presented, it can be concluded that the stress distribution was more homogeneous and less concentrated in the G1 implant-abutment assembly. Therefore, the use of abutments with dimensions standardized by the implant manufacturer is recommended.

Combustion Performance of Methane/Air in a Micro Combustor Embedded Hollow Hemispherical Slotted Bluff Body

With the rapid development of micro-energy power systems, the performance of micro-combustors as key components is in urgent need of further improvement. Aimed at enhancing combustion performance, a hollow hemispherical bluff body was used to analyze the methane combustion process. In this paper, we exploited the detailed reaction mechanism of methane/air with a laminar finite-rate model; the numerical analysis of methane combustion in the micro-combustor was carried out by Ansys Fluent software. The combustion, flow and thermal characteristics of the micro-combustor embedded with a hollow hemisphere bluff body (MCEHB) and the micro combustor embedded with a slotted hollow hemisphere bluff body (MCESHB) are compared, and the effect of slot width ratio on the combustion characteristics and thermal performance is discussed in detail. The results showed that the bluff body slotting treatment is not only beneficial to improving the velocity and temperature distribution behind the bluff body but also can improve the conversion rate of methane, especially at high inlet velocities. However, the conversion rate of methane is also affected by the slot width. When the slot width ratio below 0.5, the slot width corresponding to the peak methane conversion increased with the inlet velocity. Moreover, the bluff body slotting treatment can improve the wall temperature distribution, meanwhile expanding the high temperature area at the inner wall, thereby reducing the wall temperature fluctuation in the rear part of the micro-combustor. In addition, the optimal slot width ratio B increases with the inlet velocity. Since the inlet velocity is lower than 0.5 m/s, the optimal slot width ratio B is in the range of 0.3–0.375. However, as the inlet velocity exceeds 0.5 m/s, the optimal slot width ratio B moves to the range of 0.375–0.553. Furthermore, both large and small slot widths bring obvious temperature fluctuations to the micro combustor; the uneven wall temperature distribution phenomenon is detrimental to working performance. Therefore, the slot width ratio B of 0.375 only brings slight temperature fluctuations, indicating this is an optimal slot width ratio that should be chosen. This work has reference value for optimizing the design of the bluff body structure and improving the combustion performance of methane in the micro combustor.

Improvement of Mass Transfer Rate Modeling for Prediction of Cavitating Flow

This study proposes and investigates the impact of a modification, accounting for the influence of vortices and flow properties on the liquid rupture, to improve the modeling of mass transfer rate in cavitation. The threshold phase-change pressure is calculated by the fluid-saturated pressure at rest and the added vortex pressure term. The explicit simulation of the fully turbulent, homogeneous compressible, cavitating flow around the NACA0015 hydrofoil and the hemispherical body is performed. Saito cavitation model and Wilcox k-ω turbulence model are implemented for the evaluation of the proposed modification. The pressure coefficient distribution -Cp and cavitation behavior, including the vapor formation-collapse processes and the flow mechanism, are investigated. The analysis shows that the present modification, coupled the local flow viscosity with the vorticity magnitude, making the cavitation model better sensitive to the flow condition. The modification has a weak impact on the steady sheet cavitation around a hemispherical body but is the key factor underlying the improvement in the predicted complex flow around the NACA0015 hydrofoil. In that, the predicted -Cp and cavity structure around the hydrofoil is improved in comparison with the existing numerical data by other research groups and that by the Singhal turbulent pressure fluctuation model‎.

Creep-fatigue interaction on estimation of lifetime and fatigue damage of F82H

In this study, creep-fatigue (CF) tests on F82H at 823 K were conducted according to the standard specimen and requirement of ASTM. Tension holding (TH) showed higher lifetime than compression holding (CH). Compared with 9Cr-1Mo-V steels, CF lifetime degradation was not observed at the holding time less than 0.05 h in case of CH and 0.17 h in case of TH. CF damages were summarized from the CF test results by Campbell method. The obtained damages distributed around CF damage envelope of Grade 91 in ASME NH. CF damage of cylindrical water-cooled ceramic breeder (WCCB) test blanket module (TBM) container at the zenith of hemisphere body under the ITER thermo-mechanical load was calculated. The calculated damage located within of the damage envelope of Grade 91. It was indicated that the present design of cylindrical WCCB TBM might resist CF interaction under the ITER thermo-mechanical load conditions.

Development of pharmacognostic parameters for the leaf of Bridelia scandens (Roxb.) Willd

Background: Pharmacognostic study of medicinal plants is an important parameter for standardization and authentication of plants, with the help of which adulteration and substitution can be prevented. The present study deals with pharmacognostic profile of leaf of Bridelia scandens (Roxb).Willd. an important traditional plant, belonging to family Euphorbiaceae used to treat various ailments. Methods: The present study includes macroscopic and microscopic studies, quantitative microscopy, and physiochemical characters such as ash value, extractive values, fluorescence analysis, and total phenol and flavonoid content. Results: Macroscopically, the leaves are B. scandens are elliptic –oblong or obavate, dark green above, pale green below lateral veins. Microscopically, leaf consists of thick semicircular midrib and the lamina, cortical zone ending with thick continuous cylinder of sclerenchyma cells. Sclerenchyma cylinder completely enclosed the vascular cylinder of the midrib, consists of only continuous thick layer of phloem. Xylem cylinder consists of numerous short or long radial chains of vessels. The lateral vein is flat on the adaxial side and prominently projecting hemispherical body on the adaxial side. Powder microscopy of leaf revealed the presence of spiral xylem vessels, rosette and prismatic calcium oxalate crystals and trichomes. A Physiochemical characteristic was also determined. Conclusion: Existing literature revealed that so far, no Pharmacognostic study has been reported on the leaf of B. scandens. Findings from this investigation can be used for its identification and determination of quality and purity of medicinally important plant. Thus exploring the usefulness of pharmacognostic evaluation to validate and authenticate drug.

Free convection heat transfer from a concave hemispherical surface: A numerical exercise

Numerical investigation on a concave hemispherical surface to discover the thermo-fluid characteristics due to laminar free convection is carried out. In this study, numerical simulations of continuity, momentum, and energy equation are performed for the concave hemispherical surface using ANSYS FLUENT 19. The salient parameters such as the dimensionless radius of curvature of the hemispherical surface (from 1 to 5), Rayleigh number (from1.5 × 103 to 1.5 × 107) and surface temperature (from 350 K to 500 K) is varied to perform a parametric study. It is observed that the Nusselt number rises with the Rayleigh number for the different radius of curvatures. However, with a rise in curvature radius, the heat transfer rate marginally increases at a lower Rayleigh number, whereas it steeply increases for higher Rayleigh number values. The variation of local heat transfer coefficient along the curved surface is displayed. The velocity vector field and temperature plume around the hemispherical body clearly illustrate the convection characteristics. A Nusselt number relationship is also obtained for the concave hemispherical surface, which was not reported earlier, and this relationship is accurate within ±6%.

A Comparative Study on Aerodynamic Drag Reduction of a Blunt Nose Body using Aerospike and Aerodisk – Numerical Approach

A spike attached to a hemispherical body drastically changes its flow field and influences aerodynamic drag in supersonic and hypersonic flow. It is, therefore a potential candidate for drag reduction of a future high-speed vehicle. The effect of spike nose configuration and angle of attack on the reduction of drag is studied. The studies show that the aerodisk is superior to the aerospike. The aerodisk of appropriate length, diameter and nose configuration may have the capability for the drag reduction. Design criteria is studied and the aerodisk attached to the blunt nose body are designed using CATIA. Numerical solutions are obtained using a commercial CFD software ANSYS-Fluent. Flow observations on the blunt body with a conical, hemispherical aerodisk and flat-faced aerodisk are carried out at Mach number of 2. The flow fields show different flow features between the conical spike, the hemispherical aerodisk and the flat-faced aerodisk. The effects of the aerospike and aerodisk on the lift and drag coefficient are studied. Finally, it is found that A forward-facing spike attached to a hemispherical body alters significantly the structure of the flow field and serves to reduce drag by the formation of a recirculation region around the stagnation point of the blunt body. The flow field, immediately behind the aerodisk shows a complex flow field due to back-disk geometry as compared to the conical spike. To take advantage of the forward-facing spike for more efficient drag reduction, the reattachment point of the shear layer on the body should be moved backward by choosing the optimal spike length with suitable geometrical configuration of the nose.

Investigation of Reduction in Base Drag using Experiment and CFD at Subsonic Speed Regimes

Base drag, arising from flow separation at the blunt base of a body can be a sizeable fraction of total drag in the context of projectiles, missiles and after bodies of fighter aircrafts. The base drag is the major contribution of total drag for low speed regimes, flight tests have shown that the base drag may account for up to 50% of the total drag. Computational and experimental investigation for a hemispherical flight vehicle body of length 500mm and diameter 50mm was conducted for the purpose of investigating the base drag. Three case studies were conducted to investigate the properties of the flow field around the flight vehicle at different flow velocities of 20m/s, 30m/s and 50m/s at zero angle of attack (AoA). The three cases were (i) a flight vehicle with flat base configuration, (ii) a flight vehicle with a nozzle at the base and (iii) a flight vehicle configuration with a boat tail, Fig 1. Also, the three configurations were investigated at different AoA of -2ï‚°, 0ï‚° and +2ï‚°. The base drags for three configurations are calculated and the experimental results are compared with the CFD results.

Improvement of cavitation mass transfer modeling by including Rayleigh–Plesset​ equation second order term

The current study evaluates the effect of taking into account the second order term of the Rayleigh–Plesset equation for the numerical simulation of cavitation with homogeneous mixture models. For that, the corrected expression for the condensation mass transfer rate has been mathematically derived and implemented in the original Zwart and Singhal cavitation models. Two tests cases of steady sheet cavitation around a NACA 0009 hydrofoil and a hemi-spherical body at different cavitation coefficients have been simulated with both the original and the corrected models. The results demonstrate that the pressure distribution at the closure region of the attached cavity is better predicted and a stronger pressure gradient is obtained. Consequently, the cavity length is slightly shortened and it gets closer to the experimental observations. Another test case of cloud cavitation around a NACA 0009 hydrofoil has confirmed that the prediction of the shedding frequency is also improved with the corrected Zwart model because the maximum cavity length is significantly reduced. In conclusion, the proposed modification of the Zwart and Singhal cavitation models helps to ameliorate the numerical simulation of both steady and unsteady cavitation flows.

Strain rate effect of steel-concrete composite panel indented by a hemispherical rigid body

This paper presents numerical and theoretical investigations on the strain rate in steel-concrete composite (SC) panels under low-velocity impact of a hemispherical rigid body. Finite element analyses were performed on five specimens with different loading rates. The impact energy was kept constant to eliminate its influence by simultaneously altering the velocity and mass of the projectile. Results show that the strain rate in most parts of the specimens was low and its influence on bearing capacity and energy dissipation was limited in an average sense of space and time. Therefore, the strain rate effect can be ignored for the analyses of global deformation. However, the strain rate effect should be considered in local contact problems. Equations of the local strain and strain rate were theoretically derived.

MATHEMATIC SIMULATION OF GENERALIZED PROBLEM OF HEAT-EXCHANGE IN THE BODIES WITH HEMISPHERICAL SHAPE

The article presents the first mathematical model for calculating temperature fields of hemispherical bodies, which approximately simulates operation of the diamond-drilling bit and takes into account angular velocity of drilling operations and finite velocity of heat conduction, and which was created as a physicomathematical boundary problem for hyperbolic equation of heat conduction with the Dirichlet boundary conditions. Besides, a new integral transformation was formulated for the two-dimensional finite space, with the help of which and with the help of finite element method and Galerkin method a temperature field was found in the form of convergence series.

The Design and Validation of a Thermal Boundary Layer Wall Plate

A feedback controlled thermal wall plate designed to investigate thermal boundary layer flows is described and validated. The unique capabilities of the design are the ability to modify the thermal boundary conditions in a variety of ways or to hold the wall-temperature fixed even when the flow above the wall is unsteady and strongly three-dimensional. These capabilities allow for the generation and study of thermal transport in nonequilibrium boundary layer flows driven by different perturbations and of varying complexity. The thermal wall plate and the experimental facility in which the thermal wall plate is installed are first described. The wall-plate is then validated in a zero-pressure-gradient (ZPG) boundary layer flow for conditions of a uniform wall temperature and a temperature step. It is then shown that the wall temperature can be held constant even when a hemisphere body is placed on the wall that produces large localized variations in the convective heat transfer coefficient. Last, since the thermal wall plate is intended to support the study of thermal transport in a variety of nonequilibrium boundary layer flow, several possible experimental configurations are presented and described.

Characterization of nodular structure in shale with a proposed growth model in the Sitakund anticline, Bengal basin, Bangladesh

Nodular shales commonly occur in silty shales near the axial (proximity to core) regions of anticlinal structures (Sitakund anticline, Sitapahar anticline, Patharia structure, and Mirinja anticline) of eastern fold belt of Bangladesh. Stratigraphically, they are pronounced in the Surma group of Neogene succession. In many outcrops, these are found in the incompetent beds bounded by the competent ones. An initial investigation has been followed by comprehensive petrographical and geochemical studies including thin section microscopy, laser particle size analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray fluorescence (XRF) to characterize the nodular shale of Sitakund structure. From laser diffraction analysis, it is evident that nodular shales are silty in nature containing approximately 60% silt (mainly quartz). XRD pattern shows that nodular shale contains quartz, feldspar, illite, kaolinite, chlorite, and expandable mixed layer clay mineral including minor amount of calcite and siderite. Geochemical analysis shows that there is no significant variation from host rocks in context of major and trace element concentration. Microcracks within the quartz grains and squeezed clay minerals were observed in some nodular shale samples correlating the influence of regional tectonics and local structural dynamics in the axial regime of the anticline. Projection of 15 nodular shale long axes in outcrop shows their orientation in NNW-SSE that is parallel to the fold axis. The study suggests a new name of conventionally called nodular shales based on their origin, composition, and occurrence. The proposed name is “Clay Cabbage”. Diagenesis involving the conversion of montmorillonite to illite clay through a mixed layer illite/montmorillonite along with the regional and local tectonics is responsible for the formation of nodular shale. A new model naming as “Tectono-Diagenetic (TD) Model” is proposed in this study concerning the origin of nodular shale. Fluid pressure during diagenesis along with axial deformation due to folding produces hemispherical bodies by brittle and plastic flow that initiates the core of nodular shale at greater depth. Spiral geometry of the body is attained through several deformation stages with the evolution of the folded pattern.

Hypersonic Flow over Hemispherical Blunt Body with Spikes

Use of spike on a hemispherical body changes the flow fi eld and hence the aerodynamic drag. Computational studies have been made to obtain the fl ow fi eld around a hemispherical body with spikes at a hypersonic Mach number of 6. The effect of shape of spike tip and length has been studied. Laminar computations have been made adopting structured grid using commercial software Fluent. It is observed that use of a sharp spike itself reduces the drag signi cantly. However the use of a hemispherical head spike further reduces the drag. Contribution of dierent components towards drag indicate that the increase in length of a spike do not change the spike contribution. However the flow field on main body is altered which leads to reduction in dragwith change in length. Estimated maximum drag obtained is found to be highest in comparison to any reported drag value in literatures with any spike shape and length.

Numerical Investigation of the Turbulent Cavitating Flow over Submerged Bodies

A numerical method for the calculation of turbulent cavitating flow over submerged objects is proposed in present work. Cavitation is modeled via a single-fluid cavitation model which is derived based on a truncated form of the Rayleigh-Plesset equation and the mixture multiphase theory. The approach has been implemented by user-define function which is widely used in ANSYS FLUENT. Detailed results are presented for sheet cavitation over a submerged hemispherical object in a wide range of cavitation numbers and the cloud cavitation around a Clark-Y hydrofoil. In particular, for the hemispherical body, we compared the surface pressure distribution with experimental data which was available in literature. Later the cloud cavitation structure and its effect on the forces of the hydrofoil were studied. The comparisons between the simulating and experimental results show that present numerical approach has good capability to predict the surface pressure coefficient and the pulsation frequency at cavitation number σ=0.4, 0.55 and 0.65 of the hemispherical body under cavitation conditions. Meanwhile, for the hydrofoil, the proposed approach is sufficiently robust to predict the characteristics of the time-averaged lift and drag coefficients and the evolution of the cloud cavity with time.

Drag reduction of supersonic blunt bodies using opposing jet and nozzle geometric variations

Passive and active flow control methods are used to manipulate flow fields to reduce acoustic signature, aerodynamic drag and heating experienced by blunt bodies flying at supersonic and hypersonic speeds. This paper investigate the use of active opposing jet concept in combination with geometric variations of the opposing jet nozzle to alleviate high wave drag formation. A numerical study is conducted to observe the effects of simple jet as well as jet emanating from a divergent nozzle located at the nose of a blunt hemispherical body. An initial discussion is presented of the complex shock wave pattern flow physics occurring when opposing jet ejected from a nozzle under various operating conditions interacts with the free stream flow. The complex flow physics that include long penetration and short penetration mode is studied in conjunction with effect on drag. The numerical setup consists of supersonic free stream flow interacting with an opposing sonic jet under varying pressure ratios. Initial computational results are validated by identifying prominent flow features as well as comparing available experimental data of surface pressure distributions. Preliminary validation is followed by the introduction of a divergent nozzle in the blunt body nose region. A series of numerical iterations are performed by varying nozzle geometric parameters that include nozzle divergent angle and nozzle length for a certain jet pressure ratio. Long penetration mode, short penetration mode as well as flow separations are captured accurately during the analysis. The results show a considerable reduction in drag by the use of a divergent nozzle. Specifically, 46% and 56% reduction in drag coefficient is achieved at pressure ratio of 0.6 and 0.8 respectively in the divergent nozzle cases as compared to the simple blunt body without any nozzle.

Shock interactions in hypersonic flows outside the sonic circle in front of a blunt body

The problem of shock–shock interaction between a planar oblique shock wave and a bow shock wave is undertaken by considering a wedge and a hemispherical body in a hypersonic flow. The interaction patterns, as classified by Edney, namely Type-I, Type-II, Type-V, and Type-VI, which appear when a planar oblique shock wave interacts the bow shock wave outside the sonic circle are presented. The experiments are conducted at Mach number of 5.62, with air as test gas, in the short duration Hypersonic Shock Tunnel – 2 (HST-2) at Indian Institute of Science, Bangalore. Schlieren visualization is used to capture and identify the shock interaction patterns. Time evolution of the flow using the schlieren images is correlated with the pitot pressure signal to mark the flow establishment and useful test time in the tunnel, during which measurements are taken. Surface convective heat transfer rates are measured using Platinum thin film technique to quantify the heat transfer rates on the surface of a blunt body in the presence of these shock interactions.

Towards a quantitative comparison between global and local stability analysis

A methodology is proposed here to estimate the stability characteristics of bluff-body wakes using local analysis under the assumption of weakly non-parallel flows. In this connection, a generalisation of the classic spatio-temporal stability analysis for fully three-dimensional flows is first described. Secondly, an additional higher-order correction term with respect to the common saddle-point global frequency estimation is included in the analysis. The proposed method is first validated for the case of the flow past a circular cylinder and then applied to two fully three-dimensional flows: the boundary layer flow over a wall-mounted hemispherical body and the wake flow past a fixed sphere. In all the cases considered, both the estimated unstable eigenvalue and the spatial shape of the associated eigenmode are determined by local stability analysis, and they are compared with the reference counterparts obtained at a definitely higher computational cost by a fully three-dimensional global stability analysis. It is shown that the results of local stability analysis, when the higher-order correction term is included, are in excellent agreement with those obtained by global stability analysis. It is also shown that the retained correction term is of crucial importance in this perspective, leading to a remarkable improvement in accuracy with respect to the classical saddle-point estimation.