Hypersonic Boundary Layer Receptivity to Acoustic Disturbances Over Cones

The receptivity mechanisms of hypersonic boundary layers to free stream acoustic disturbances are studied using both linear stability theory (LST) and direct numerical simulations (DNS). A computational code is developed for numerical simulation of steady and unsteady hypersonic flow over cones by combining a fifth-order weighted essentially non-oscillatory (WENO) scheme with third-order total-variation-diminishing (TVD) Runge-Kutta method. Hypersonic boundary layer receptivity to free-stream acoustic disturbances in slow and fast modes over 5-degree, half-angle blunt cones and wedges are numerically investigated. The free-stream Mach number is 6.0, and the unit Reynolds number is 7.8×106/ft. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations in two-dimensional and axisymmetric coordinates. Computations are performed in three steps. After the steady mean flow field is computed, linear stability analysis is performed to find the most amplified frequency and the unstable disturbance modes in different flow regions. Then time accurate computations are performed using slow and fast mode acoustic disturbances, and the initial generation, interaction and evolution of instability waves inside the boundary layers are studied. Receptivity computations showed that the acoustic disturbance waves propagated uniformly to downstream, interact with the bow shock, enter the boundary layer, and then generate the initial amplitude of the instability waves in the leading edge region. Effects of the entropy layer due to nose bluntness to the receptivity process are studied. It is found that transition location moves downstream and is delayed by increasing bluntness, and the role of the entropy layer in this process is revealed. Also, the effects of wall cooling to the receptivity process using slow and fast mode acoustic disturbances are studied. The effects of cooling on the first and second mode regions are investigated. It is found that the first mode is stabilized and the second mode is destabilized by wall cooling when the flow is forced by acoustic waves in the slow mode

Effects of Nose Bluntness on Hypersonic Boundary-Layer Receptivity and Stability Over Cones

The receptivity to freestream acoustic disturbances and the stability properties of hypersonic boundary layers are numerically investigated for boundary-layer flows over a 5 straight cone at a freestream Mach number of 6.0. To compute the shock and the interaction of the shock with the instability waves, the Navier-Stokes equations in axisymmetric coordinates were solved. In the governing equations, inviscid and viscous flux vectors are discretized using a fifth-order accurate weighted-essentially-non-oscillatory scheme. A third-order accurate total-variation-diminishing Runge-Kutta scheme is employed for time integration. After the mean flow field is computed, disturbances are introduced at the upstream end of the computational domain. The appearance of instability waves near the nose region and the receptivity of the boundary layer with respect to slow mode acoustic waves are investigated. Computations confirm the stabilizing effect of nose bluntness and the role of the entropy layer in the delay of boundary-layer transition. The current solutions, compared with experimental observations and other computational results, exhibit good agreement

Towards exascale DNS solver for hypersonic boundary-layer receptivity to solid particulates

Development in hypersonic vehicles is dependent on the prediction of hypersonic boundary-layer transition location from a laminar to turbulent state because aerodynamic heating, drag force, engine performance, and vehicle operation are highly affected by the boundary-layer transition. To make precise prediction about boundary-layer transition points, it is required to understand the fundamental physics behind it. Although some key mechanisms are enlightened with recent studies, there are still unsolved part of this complex physics. Process of transformation of external disturbances into instability waves which grow in the downstream and causes to turbulence is called as receptivity. Small solid particles suspended in the atmosphere may be a significant source of boundary-layer instabilities. Their sizes in micro scales. Since particulate sizes are very small, fine meshes are used to catch the small disturbances that is induced by these small particulates and this makes parallelizing the solver inevitable. For more complex cases, heterogonous and exascale computing is required to obtain the results in a practical time period. In this poster, progress towards a physics-based parallel direct numerical simulation (DNS) tool to simulate the dynamic interaction of particulates, particulate-induced vortical disturbances, acoustic waves, and surface roughness with boundary-layer from the first principles will be presented.Mechanical and Aerospace Engineerin

Interface learning of multiphysics and multiscale systems

Complex natural or engineered systems comprise multiple characteristic scales, multiple spatiotemporal domains, and even multiple physical closure laws. To address such challenges, we introduce an interface learning paradigm and put forth a data-driven closure approach based on memory embedding to provide physically correct boundary conditions at the interface. To enable the interface learning for hyperbolic systems by considering the domain of influence and wave structures into account, we put forth the concept of upwind learning towards a physics-informed domain decomposition. The promise of the proposed approach is shown for a set of canonical illustrative problems. We highlight that high-performance computing environments can benefit from this methodology to reduce communication costs among processing units in emerging machine learning ready heterogeneous platforms toward exascale era

Multifidelity Computing for Coupling Full and Reduced Order Models

Hybrid physics-machine learning models are increasingly being used in simulations of transport processes. Many complex multiphysics systems relevant to scientific and engineering applications include multiple spatiotemporal scales and comprise a multifidelity problem sharing an interface between various formulations or heterogeneous computational entities. To this end, we present a robust hybrid analysis and modeling approach combining a physics-based full order model (FOM) and a data-driven reduced order model (ROM) to form the building blocks of an integrated approach among mixed fidelity descriptions toward predictive digital twin technologies. At the interface, we introduce a long short-term memory network to bridge these high and low-fidelity models in various forms of interfacial error correction or prolongation. The proposed interface learning approaches are tested as a new way to address ROM-FOM coupling problems solving nonlinear advection-diffusion flow situations with a bifidelity setup that captures the essence of a broad class of transport processes

Challenges Faced by Adult Learners in Online Distance Education: A Literature Review

Although online distance education provides adult learners with an opportunity for life-long learning, there are still factors challenging them to engage in educational processes. The purpose of this study is to explore the challenges faced by adult learners in online distance education through the analysis of the relevant literature. The articles (N=36) published in the key journals in the fields of open and distance education, instructional technology, and adult education were reviewed and analyzed through constant comparative analysis in the current study. The findings reveal that adult learners have challenges related to internal, external, and program-related factors indicating the interrelated nature of these challenges. The findings also show that the challenges experienced by adult learners vary depending on their age, gender, knowledge and skills as well as the context in which they study. The findings of this study, which has an exploratory nature, have several implications for distance education stakeholders such as administrators, instructors, instructional designers, and policy makers

Investigation of airflow around buildings using Large-Eddy Simulations for Unmanned Aircraft Systems applications

The ever-increasing demand for Unmanned Aircraft Systems (UAS) has led to the desire for integrating them into spaces in close proximity of humans like dense urban spaces, a reality previously thought of as inconceivable. One of the main concerns to be addressed before its widespread adoption is safety, especially in areas of operation adjacent to structures like buildings. This work investigates the effect of building geometries on the flow field in a simplified urban setup consisting of an isolated building to predict their potential impacts on UAS operations. Unanticipated wind gusts or turbulent flow conditions prevalent around various structures constitute a significant challenge for UAS operations in urban environments. We use Large-Eddy Simulation to better understand the unsteady and highly coherent turbulent flow structures produced by buildings in neutral atmospheric boundary layer flow. Furthermore, we also demonstrate a non-intrusive machine learning methodology to predict flow fields to augment safe wind-aware navigation systems for Unmanned Aerial Vehicles as a first step towards safely integrating UAS into existing aerial infrastructure.Mechanical and Aerospace Engineerin

Volume CXIV, Number 4, November 7, 1996

Objective: Turner syndrome (TS) is a chromosomal disorder caused by complete or partial X chromosome monosomy that manifests various clinical features depending on the karyotype and on the genetic background of affected girls. This study aimed to systematically investigate the key clinical features of TS in relationship to karyotype in a large pediatric Turkish patient population.Methods: Our retrospective study included 842 karyotype-proven TS patients aged 0-18 years who were evaluated in 35 different centers in Turkey in the years 2013-2014.Results: The most common karyotype was 45,X (50.7%), followed by 45,X/46,XX (10.8%), 46,X,i(Xq) (10.1%) and 45,X/46,X,i(Xq) (9.5%). Mean age at diagnosis was 10.2±4.4 years. The most common presenting complaints were short stature and delayed puberty. Among patients diagnosed before age one year, the ratio of karyotype 45,X was significantly higher than that of other karyotype groups. Cardiac defects (bicuspid aortic valve, coarctation of the aorta and aortic stenosis) were the most common congenital anomalies, occurring in 25% of the TS cases. This was followed by urinary system anomalies (horseshoe kidney, double collector duct system and renal rotation) detected in 16.3%. Hashimoto's thyroiditis was found in 11.1% of patients, gastrointestinal abnormalities in 8.9%, ear nose and throat problems in 22.6%, dermatologic problems in 21.8% and osteoporosis in 15.3%. Learning difficulties and/or psychosocial problems were encountered in 39.1%. Insulin resistance and impaired fasting glucose were detected in 3.4% and 2.2%, respectively. Dyslipidemia prevalence was 11.4%.Conclusion: This comprehensive study systematically evaluated the largest group of karyotype-proven TS girls to date. The karyotype distribution, congenital anomaly and comorbidity profile closely parallel that from other countries and support the need for close medical surveillance of these complex patients throughout their lifespa

A CFD Tutorial in Julia: Introduction to Compressible Laminar Boundary-Layer Flows

A boundary-layer is a thin fluid layer near a solid surface, and viscous effects dominate it. The laminar boundary-layer calculations appear in many aerodynamics problems, including skin friction drag, flow separation, and aerodynamic heating. A student must understand the flow physics and the numerical implementation to conduct successful simulations in advanced undergraduate- and graduate-level fluid dynamics/aerodynamics courses. Numerical simulations require writing computer codes. Therefore, choosing a fast and user-friendly programming language is essential to reduce code development and simulation times. Julia is a new programming language that combines performance and productivity. The present study derived the compressible Blasius equations from Navier–Stokes equations and numerically solved the resulting equations using the Julia programming language. The fourth-order Runge–Kutta method is used for the numerical discretization, and Newton’s iteration method is employed to calculate the missing boundary condition. In addition, Burgers’, heat, and compressible Blasius equations are solved both in Julia and MATLAB. The runtime comparison showed that Julia with for loops is 2.5 to 120 times faster than MATLAB. We also released the Julia codes on our GitHub page to shorten the learning curve for interested readers

The effect of vegetable and animal oils added to different forages and concentrates on the in vitro fermentation parameters in ruminants

This study aimed to determine the effects of fermentation parameters of sunflower oil, vegetable oil blend, palm oil and chicken oil addition to sunflower meal, wheat grain, alfalfa herbage and corn silage at different rates (4% and 6%, dry matter basis). The oil supplementation up to 6% rate to the alfalfa herbage and corn silage did not adversely affect the level of in vitro gas production, metabolic energy (ME), net energy lactation (NEL), organic matter digestion (OMD) and molarities of acetic, propionic, butyric, iso-valeric, iso-butyric and valeric acids and number of total protozoa (P> 0.05). The oil supplementation to alfalfa herbage increased molarities of butyric, iso-valeric, iso-butyric and valeric adds and number of total protozoa (except sunflower oil) in rumen fluid (P < 0.05). Palm oil decreased the in vitro gas production, ME, NEL and OMD values of sunflower meal (P < 0.05). Supplementation of vegetable oil blend to wheat grain increased ME, NE L and OMD values and butyric acid molarity in rumen fluid (P < 0.05). The in vitro ruminal ammonia-nitrogen concentrations of alfalfa herbage and corn silage increased by vegetable oil blend, palm oil and chicken oil up to 6% (P < 0.05). As a result, the nutrient content of the feedstuffs used changed the in vitro ruminal fermentation values of the oil additive to be added. The addition of sunflower oil, vegetable oil blend, palm oil and chicken oil at 4% and 6% rates to corn silage, alfalfa herbage, sunflower meal and wheat grain feed found to differ on in vitro ruminal fermentation parameters