One-Dimensional and Axisymmetric Numerical Simulation of a Single-Stage Gas Gun

Abstract One dimensional and axisymmetric numerical simulation of a single-stage gas gun is being conducted in this study. Axisymmetric viscous and compressible flow equations has been numerically solved by van Leer flux vector splitting scheme, with space and time second order accuracy by using moving boundary. One dimensional inviscid compressible flow has been numerically solved by secondorder Roe TVD scheme. For the turbulent flow in axisymmetric simulation is used the Baldwin-Lomax model. The projectile velocity for different governing parameters for a transonic and supersonic gas gun is obtained and investigated. The transonic gas gun results illustrate that the second-order TVD Roe scheme has a higher accuracy than the Van Leer flux vector splitting scheme for low Mach number flows. The supersonic gas gun results are in an excellent agreement with the one-dimensional and axisymmetric simulation. The comparison between two methods of solution shows that the one-dimensional and inviscid flow approximation are sufficient for simulation of flow in a single-stage gas gun and does not need to the axisymmetric simulation

Analytical Solution for Different Profiles of Fin with Temperature-Dependent Thermal Conductivity

Three different profiles of the straight fin that has a temperature-dependent thermal conductivity are investigated by differential transformation method (DTM) and compared with numerical solution. Fin profiles are rectangular, convex, and exponential. For validation of the DTM, the heat equation is solved numerically by the fourth-order Runge-Kutta method. The temperature distribution, fin efficiency, and fin heat transfer rate are presented for three fin profiles and a range of values of heat transfer parameters. DTM results indicate that series converge rapidly with high accuracy. The efficiency and base temperature of the exponential profile are higher than the rectangular and the convex profiles. The results indicate that the numerical data and analytical method are in agreement with each other

United Nations Educational Scientific and Cultural Organization and International Atomic Energy Agency THE ABDUS SALAM INTERNATIONAL CENTRE FOR THEORETICAL PHYSICS MODIFIED k-£ MODEL AND ITS ABILITY TO SIMULATE SUPERSONIC AXISYMMETRIC TURBULENT FLOWS

Abstract The k-£ turbulence model is a promising two-equation model. In this paper, the k and I model equations were derived from k-k^ incompressible and one-equation turbulence models. Then the model was modified for compressible and transitional flows, and was applied to simulate supersonic axisymmetric flows over Hollow cylinder flare and hyperboloid flare bodies. The results were compared with the results obtained for the same flows experimentally as well as k-e, k-oo and Baldwin-Lomax models. It was shown that the kt model produces good results compared with experimental data and numerical data obtained when other turbulence models were used. It gives better results than k-co and k-e models in some cases. MIRAMARE -TRIESTE May Introduction Supersonic axisymmetric flows are important in aerodynamics and turbomachinery among other applications. A turbulence model must have the ability to simulate complicated high speed the flows, which contain the recirculation zone, expansion and compression waves and their interaction with other high speed flow phenomena, with a certain degree of accuracy. In the last thirty years, the majority of research works that have been done in turbulence modeling correspond to k-E models. The k-co equation is the second two-equation model that was recently tackled by other researchers, for example see [1]. In this study, the k-£ two-equation turbulence model is derived and tested for the axisymmetric blunt body flows with recompression corner. The turbulence length scale equation is much easier to resolve numerically than the turbulent dissipation and turbulent vorticity equations that were used in the k-E and k-co models, respectively. The k-E model overestimates the skin friction coefficient when applied to the boundary layer flows with adverse pressure gradient. The k-co equation is sensitive to free stream boundary conditions. Sarkar [2] and Zemman The k-£ equations have gained much less attention by researchers. Smith [6,7] introduced a transport equation for length scale and applied it to boundary layer flows with success. In this paper, the k-£ equations were first derived from Saeedi et at [8] k-k^ model. Then they were modified to simulate supersonics flows and transition region. In this paper k-£, k-e, k-co and Baldwin-Lomax [9] turbulence models, were used to simulate supersonic flow over a hollow cylinder flare, and a hyperbolic-flare body bow shock. The modifications introduced by Sarkar [2] and Zemma

Inverse hyperbolic heat conduction in fins with arbitrary profiles

This study aims to estimate unknown base temperature distribution in different non-Fourier fins. The Cattaneo-Vernotte (CV) heat model is used to predict the heat conduction behavior in these fins. This inverse problem is solved by the function-estimation version of the Adjoint conjugate gradient method (ACGM) based on boundary temperature measurements. The ACGM includes direct, sensitivity, and adjoint problems. For each of these problems, a one-dimensional general formulation of the non-Fourier model for longitudinal fins with arbitrary profile is driven and solved by an implicit finite difference method. In this study, three different profiles are considered: triangular, convex parabolic, and concave parabolic. For each of them, two different base temperature distributions are estimated using an inverse method. Moreover, the effects of sensor positions at the fin tip and a specific place in-between are considered on the base temperature estimation. A close agreement between the exact values and the estimated results is found, confirming the validity and accuracy of the proposed method. The results show that the ACGM is an accurate and stable method to determine the thermal boundary conditions in different non-Fourier fin problem

Transonic and supersonic overtaking of a projectile preceding a shock wave

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Modified k-shell model and its ability to simulate supersonic axisymmetric turbulent flows

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

A Review on the diagnostic approaches of COVID-19 infection; Features and limitations

Detection of coronavirus disease 2019 (COVID-19) in early stage is indispensible for outcome improvement and interruption of transmission chain. Clear understanding of the nature of the diagnostic tests for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and their challenges, collecting the most diagnostically valuable specimen at the right time from the right anatomic site, and interpretation of their findings is important. This review scrutinizes current challenges and interpretation of reverse transcriptase polymerase chain reaction (RT-PCR), as the reference method, loop-mediated isothermal amplification (LAMP), antibody and antigen detection, typical lung imaging characteristics and prominent abnormal changes in laboratory findings of patients with proven COVID-19, and describes how the results may vary over time. Bronchoalveolar lavage fluid and sputum specimens demonstrate the highest positive rates (93% and 72 %, respectively) in molecular diagnosis of COVID-19. Alternatively, repeated RT-PCR assays can be performed; as over time, it is an increase in the likelihood of the SARS-CoV-2 being present in the nasopharynx. Combining clinical evidence with results of chest computed tomography (CT) and RT-PCR can minimize the risk of diagnostic errors. Elevated levels of interleukin 6 (IL‐6) and D-dimer are thought to be closely associated with the occurrence of severe COVID‐19 in adults, and their combined detection can serve as early factors predicting the severity of COVID‐19. Moreover, elevated acute phase proteins are associated with a poor outcome in COVID-19. Serological diagnosis also is an important tool to understand the extent of COVID-19 in the community, and to identify individuals, who are immune. Antibodies begin to increase from the second week of symptom onset