Effect of 3D Roughness Patch on Instability Amplification in a Supersonic Boundary Layer

Surface roughness is known to have a substantial impact on the aerothermodynamic loading of high-speed vehicles, particularly via its influence on the laminar-turbulent transition process within the boundary layer. Numerical simulations are performed to investigate the effects of a distributed region of densely packed, sinusoidal shape roughness elements on a Mach 3.5 flat plate boundary layer for flow conditions corresponding to the planned conditions of an upcoming experiment in the Mach 3.5 Supersonic Low Disturbance Tunnel at the NASA Langley Research Center. Analysis of convective instabilities in the wake of the roughness patch was reported in a previous paper and the current work extends that analysis to instability amplification across the length of the roughness patch. Quasiparallel stability analysis of the modified boundary layer flow over the patch indicates two dominant families of unstable disturbances, namely, a group of high frequency modes that amplify in localized regions along the roughness patch and another group of low frequency modes that have smaller peak amplification rates but amplify steadily both above the roughness patch and in the wake region behind it. The results suggest that the amplification factors associated with the high-frequency modes are sufficiently low, at least for the roughness patches considered in this paper, so that these modes are unlikely to have a major influence on the transition process. The amplification of the low-frequency modes within the region of the roughness patch is further quantified via direct numerical simulations. Results confirm the strongly destabilizing influence of the roughness patch on the first mode instabilities, yielding an N-factor increment of N 3.6 for a roughness patch length of eight wavelengths

Stabilization of a Swept-Wing Boundary Layer by Discrete Roughness Elements at High Reynolds Numbers

Direct numerical simulations (DNS) are performed to study potential stabilizing ef- fect of spanwise periodic discrete roughness elements (DREs) on cross ow instabilities in a spatially developing three-dimensional boundary layer over an in nite-swept natural- laminar- ow wing at a freestream Mach number of 0:75 and a chord Reynolds number of approximately 25 million. In the DNS, both the spanwise periodic DREs and distributed roughness in the leading-edge region are implemented to simulate a typical experimen- tal scenario in which multiple steady cross ow modes including the most unstable mode (i.e., the \target" mode) emerge because of the presence of naturally distributed surface roughness in the leading edge region and spanwise periodic control cylinders of subcritical wavelength are used to force small-wavelength disturbances (i.e., the control mode) for damping the target mode. The DNS results show that the e ectiveness of DRE control is sensitive to roughness diameter, height, and chordwise placement. For the DRE parame- ters considered in this study, the stabilizing e ect on the target mode is small within the computational domain that ended at about 35% of the chord

Las emociones de los profesores que enseñan alemán en las escuelas secundarias chinas

This work was supported by the Fundamental Research Funds for the Central Universities and the Funds of the Teaching Advisory Board for German majors under the Ministry of Education in China (21DYJJ06).As part of the continued effort to advocate multilingual education, China has recently included German, French, and Spanish as subjects in secondary education. Secondary teachers teaching these languages other than English (LOTEs) may confront new challenges and opportunities, potentially making their professional lives emotionally intense. We therefore take teachers teaching German in Chinese secondary schools as examples and examine their emotions, including the emotion types and the reasons behind those emotions. Using a mixed method, the study surveyed 136 Chinese German teachers nationwide, and then conducted follow-up interviews with 20 participants. The study reveals that the Chinese German teachers experienced more positive emotions than negative ones. The positive emotions were mostly associated with positive interactions in their school settings, followed by their teacher knowledge, interests, and personality, while opportunities created by the development of the German subject constituted an additional factor. Implications for how to enhance LOTE teachers’ emotional experiences are discussed.Como parte del esfuerzo continuo por promover la educación multilingüe, China ha incluido recientemente el alemán, el francés y el español como asignaturas en la educación secundaria. Los profesores de secundaria que enseñan estos idiomas distintos al inglés (LOTE) pueden enfrentarse a nuevos desafíos y oportunidades, lo que puede hacer que sus carreras profesionales sean emocionalmente intensas. Por lo tanto, tomamos como ejemplo a los profesores que enseñan alemán en las escuelas secundarias chinas y examinamos sus emociones, incluidos los tipos de emociones y las razones que subyacen a estas emociones. Utilizando un método mixto, esta investigación encuestó a 136 profesores chinos de alemán en todo el país, y luego realizó entrevistas de seguimiento con 20 participantes. El estudio revela que los profesores chinos de alemán experimentaron más emociones positivas que negativas. Las emociones positivas se asociaron en su mayoría con las interacciones positivas en sus entornos escolares, seguidas de los conocimientos, intereses y personalidad de los profesores, mientras que las oportunidades creadas por el desarrollo de la asignatura de alemán constituyeron un factor adicional. Se han discutido las implicaciones sobre cómo mejorar las experiencias emocionales de los docentes de LOTE.Fundamental Research FundsFunds of the Teaching Advisory Board (21DYJJ06

Direct Numerical Simulation of Receptivity to Roughness in a Swept-Wing Boundary Layer at High Reynolds Numbers

Direct numerical simulations (DNS) are performed to examine the receptivity to roughness in a spatially developing three-dimensional boundary layer over an in finite-swept natural-laminar-flow wing at a free stream Mach number of 0:75 and a chord Reynolds number of approximately 25 million based on the long, swept chord. Stationary cross ow disturbances are excited by applying either critically spaced discrete cylinders of micron size or naturally occurring distributed roughness in the leading-edge region. The DNS data show that the spanwise spectral content of the excited cross ow disturbances is highly dependent upon the shape of roughness elements, and the initial growth of the cross ow structures is a nonlinear function of the element height. The linear growth rate of the excited cross ow disturbances predicted by DNS shows good agreement with linear parabolized stability equations. The receptivity study lays the foundation for investigating the stabilization of the naturally most unstable steady cross ow mode by using spanwise periodic DREs

Direct Numerical Simulation of Transition Due to Traveling Crossflow Vortices

Previous simulations of laminar breakdown mechanisms associated with stationary crossflow instability over a realistic swept-wing configuration are extended to investigate the alternate scenario of transition due to secondary instability of traveling crossflow modes. Earlier analyses based on secondary instability theory and parabolized stability equations have shown that this alternate scenario is viable when the initial amplitude of the most amplified mode of the traveling crossflow instability is greater than approximately 0.03 times the initial amplitude of the most amplified stationary mode. The linear growth predictions based on the secondary instability theory and parabolized stability equations agree well with the direct numerical simulation. Nonlinear effects are initially stabilizing but subsequently lead to a rapid growth followed by the onset of transition when the amplitude of the secondary disturbance exceeds a threshold value. Similar to the breakdown of stationary vortices, the transition zone is rather short and the boundary layer becomes completely turbulent across a distance of less than 15 times the boundary layer thickness at the completion of transition

Human Resource Management Bundles and Employee Performance: A Mediated Model

This research demonstrated the impact of human resource management bundles on employee performance, both direct and mediated by human capital and organizational commitment.  The ability-enhancing, motivation-enhancing and empowerment-enhancing HRM bundles have significant direct impacts on employee performance and organizational commitment. However, only the motivation-enhancing HRM bundle has a significant direct impact on human capital.  There are also significant impacts from human capital to employee performance, organizational commitment to human capital, organizational capital to social capital and social capital to human capital. Finally, human capital has a significant relationship with employee performance. Most of the hypothesized mediated effects were also found, except that their effects were smaller than those of the direct effects. Implications of the research findings and proposals for future research are discussed

Factors Contributing to Expatriate Adjustment to Life in Malaysia

The objective of this study is to determine the factors contributing to expatriate adjustment to life in Malaysia. Drawing on the conservation of resources theory and previous research, the independent variables of cultural intelligence, language ability, open-mindedness, tenure in Malaysia, previous overseas experience and monthly income, are used in this study to predict expatriate adjustment. A survey questionnaire was developed and analysis done on 80 expatriates from four industries in Kuala Lumpur and Selangor. Results of regression analysis using the PROCESS software showed that cultural intelligence, language ability open-mindedness, tenure in Malaysia and gender explained 76.2% of the variance in expatriate adjustment in Malaysia. Furthermore, tenure in Malaysia moderated cultural intelligence. However, previous overseas assignments and monthly income did not have any relationships with expatriate adjustment. The applicability of the conservation of resources theory to explain expatriate adjustment is clearly established in this study as all the variables that are significant predictors of expatriate adjustment are resources

On Landau inequality via semigroup orbits

Let $\omega>0$. Given a strongly continuous semigroup $\{e^{tA}\}$ on a Banach space and an element $f\in\mathbf{D}(A^2)$ satisfying the exponential orbital estimates $$\|e^{tA}f\|\leq e^{-\omega t}\|f\| \quad\text{and}\quad \|e^{tA}A^2f\|\leq e^{-\omega t}\|A^2f\|,\quad t\geq0,$$ a dynamical inequality for $\|Af\|$ in terms of $\|f\|$ and $\|A^2f\|$ was derived by Herzog and Kunstmann (Studia Math., 223(1):19-26, 2014). In this note we provide an improvement of their result by relaxing the exponential decay to quadratic, together with a simple and direct way recovering the usual Landau inequality