Acoustic receptivity and transition modeling of Tollmien-Schlichting disturbances induced by distributed surface roughness

Acoustic receptivity to Tollmien-Schlichting waves in the presence of surface roughness is investigated for a flat plate boundary layer using the time-harmonic incompressible linearized Navier-Stokes equations. It is shown to be an accurate and efficient means of predicting receptivity amplitudes, and therefore to be more suitable for parametric investigations than other approaches with DNS-like accuracy. Comparison with literature provides strong evidence of the correctness of the approach, including the ability to quantify non-parallel flow effects. These effects are found to be small for the efficiency function over a wide range of frequencies and local Reynolds numbers. In the presence of a two-dimensional wavy-wall, non-parallel flow effects are quite significant, producing both wavenumber detuning and an increase in maximum amplitude. However, a smaller influence is observed when considering an oblique Tollmien-Schlichting wave. This is explained by considering the non-parallel effects on receptivity and on linear growth which may, under certain conditions, cancel each other out. Ultimately, we undertake a Monte-Carlo type uncertainty quantification analysis with two-dimensional distributed random roughness. Its power spectral density (PSD) is assumed to follow a power law with an associated uncertainty following a probabilistic Gaussian distribution. The effects of the acoustic frequency over the mean amplitude of the generated two-dimensional Tollmien-Schlichting waves are studied. A strong dependence on the mean PSD shape is observed and discussed according to the basic resonance mechanisms leading to receptivity. The growth of Tollmien-Schlichting waves is predicted with non-linear parabolized stability equations computations to assess the effects of stochasticity in transition location

Stabilization of crossflow instability with plasma actuators: linearized navier stokes simulations

This paper describes work carried out within the European Union (EU)-Russia Buterfli project to look at the control of transition-causing “target” stationary cross flow vortices, by the use of distributed plasma actuation to generate sub-dominant “killer” modes. The objective is to use the “killer” modes to control the “target” modes through a non-linear stabilizing mechanism. The numerical modelling and results are compared to experimental studies performed at the TsAGI T124 tunnel for a swept plate subject to a favorable pressure gradient flow. A mathematical model for the actuator developed at TsAGI was implemented in a linearized Navier Stokes (LNS) solver and used to model and hence predict “killer” mode amplitudes at a measurement plane in the experiment. The LNS analysis shows good agreement with experiment, and the results are used as input for non-linear PSE analysis to predict the effect of these modes on crossflow transition. Whilst the numerical model indicates a delay in transition, experimental results indicated an advance in transition rather than delay. This was determined to be due to actuator induced unsteadiness arising in the experiment, resulting in the generation of travelling crossflow disturbances which tended to obscure and thus dominate the plasma stabilized stationary disturbances

CONCEPTUAL MODELS FOR DEVELOPMENTAL NEEDS OF ACADEMIC MIDDLE MANAGERS IN HIGHER EDUCATION INSTITUTIONS

Development of employees by the Human Resources (HR) department in any organization is crucial to implementing its strategy, processes and procedures for success. The same principle applies to Higher Education Institutions (HEIs) in which academic Middle Managers (MMs) are the balancing drivers who execute organization’s vision and mission and contribute towards its goals. At faculty level, academic MMs roles include Deans, Head of Departments, Subject leaders and Principal lecturers/Programme leaders. However, emergent from contemporary literature studies shows that HEIs structures and systems are rapidly changing and highly impacting academic MMs in their roles. Thus, the changes and challenges transpiring in the HEIs sector are inducing and creating colossal pressures and workloads for academic MMs to work effectively and efficiently in their respective roles. Contributing to this burden, are factors such as; an increase in student numbers and retention, bureaucracy, accountability and reporting, policies, skills, management and leadership development and practice, globalisation and international outlook, competition and league tables, resources, technological advances, quality teaching, learning and research, providing value and creating balance. Based on these notions, the research aim is to create conceptual models for developmental needs of academic MMs in HEIs via a mixed methodology implemented in three phases. The findings of this research through qualitative enquiry identified fifteen factors during semi-structured interviews, six main categories using grounded theory approach, and eight main themes in case studies. In quantitative approach, seventeen factors using univariate analysis and sixteen factors using factor analysis were identified. The originality of this study contributed to the theory, practice and research of academic MMs developmental needs by; new interpretations of the authors in the field, testing and adding to theories, synthesizing work and offering work perspectives, carrying out innovative research in UK and detailed work across methods

Development Needs of Middle Managers In Higher Education Institutions: A Case Study of A Post 1992 New University in UK

Development of staff by Human Resources (HR) department in any organisation is crucial to implement its strategy, operations, goals and for eventual success. Similarly, in Higher Education Institutions (HEIs) the Middle Managers (MM) are drivers who execute organisation vision, mission and contribute towards its desired attainment. MM job titles at faculty level include Deans, Head of Departments, Subject leaders and Principle lecturers/Programme leaders. However, evidenced from contemporary literature, changes and challenges transpiring in HEIs sector is influencing and generating tremendous pressures and workloads for MM to work effectively and efficiently in their respective roles. Therefore, the fortitude of this study is to explore this phenomenon and capture true MM Development Needs (DN) and propose a conceptual model. In stage one (qualitative stage), a semi structured interview protocol was derived from 2 pilot semi structured interviews and literature review theoretical model. A meso case study (sub cases and individual embedded cases) of a UK Post 1992 university was conducted with 23 semi-structured interviews lasting an hour each. 14 interviews were analysed in rich detail. The major findings depict 251 themes from the qualitative data analysis categorised under 6 main categories. To validated and cross compare the themes, 9 collected interviews were audio listened to verify and validate the findings. In summary, based on stage 1 results, there is a gap in the development programmes provided by HR in HEIs, and MM requirements. Future study in Stage two (quantitative stage), will further explore MM development needs via pilot testing a survey questionnaire in the same post 1992 HEI before disseminating it externally to 141 UK HEIs providers (Gov. UK, 2017) for validation prior to proposing the final development model

Secondary instability of Mack mode disturbances in hypersonic boundary layers over micro-porous surface

In laminar hypersonic boundary layers, it is known that secondary instability plays a crucial role in transition to turbulence. The secondary instability usually includes the fundamental mode, the subharmonic mode, and the detuned mode. Considerable research exists on the secondary instability mechanism in hypersonic boundary layers with the smooth wall condition. The topic of using micro-porous surfaces for disturbance stabilization has recently drawn interest. The stabilization and, thus, a possible delay in the transition arise due to a reduction in the growth rate of the primary Mack mode by the porous surface. This paper focuses on investigating whether the secondary instability mechanism of Mack modes can also be affected by a surface porosity condition. It is known that the primary Mack mode linear disturbances are changed significantly on the porous surface, and how it subsequently influences the secondary instability of the modified time varying basic flow is our concern. The analysis demonstrates that on the porous surface, as the amplitude of the primary Mack mode increases, the fundamental mode is not stable. Instead, the fundamental mode amplifies rapidly with increasing primary amplitudes. At larger secondary instability spanwise wavenumbers, when the primary amplitude exceeds a certain threshold value, the fundamental modes surpass the subharmonic modes and dominate the secondary instability. However, when the spanwise wavenumber is relatively small, especially at the spanwise wavenumber corresponding to the maximum growth rate of the subharmonic mode, the fundamental modes are weakened and lose their dominant position. We find that corresponding to different amplitudes of primary Mack mode disturbances affected by the porosity parameters, there are no strongly preferred interaction modes that dominate the secondary instability; this contrasts with smooth wall findings. We further find that the larger the pore size or porosity, the more severe the suppression of the fundamental mode

Parents\u27 Desire to Change Phone Use: Associations with Objective Smartphone Use and Feelings About Problematic Use and Distraction.

We examined objective smartphone use (via a mobile sensing application) and self-reported desire to change phone use among a sample of 268 U.S. parents of infants. Using the Transtheoretical Stages of Change model as a conceptual foundation, we contextualized their attitudes and behaviors and explored how phone use and desire to change relate to perceptions of distraction and problematic phone use around their child. Latent profile analysis of parents\u27 precontemplation, contemplation, and action scores revealed two classes-precontemplators (15%) and contemplators (85%). Contemplators-those considering or desiring change-showed more bedtime phone use and general social networking than precontemplors; however, there were no significant differences between groups on other objective use measures (e.g., total daily duration of phone use, phone use around child, etc.). Contemplators also showed greater perceptions of problematic use around their child and parenting distraction. Moreover, parents\u27 problematic use and distraction were predictive of higher contemplation scores, even after controlling for demographic and objective phone use variables. Taken together, these results suggest that perceptions of phone use as problematic may be more important than actual phone habits, especially total phone use duration, for desire to change. Suggestions for future research and intervention are provided

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability