Study of effect of flow parameters on base pressure in a suddenly expanded duct at supersonic mach number regimes using CFD and design of experiments

Effectiveness of active control of micro jets has been examined by conducting experiments through an abruptly expanded axi-symmetric duct in a view to control base pressure. For this purpose, 1mm orifice diameter micro jets have been deployed at an interval of 900 along the exit diameter of the nozzle. The experiments have been conducted by considering three flow parameters at three levels. Mach number (M), length to diameter (L/D) ratio and area ratio (AR) are the three parameters used to conduct and analyze the flow experiments. Base pressure is considered to be the response variable. The experimentation has been carried out for two cases, i) without active control; ii) with active control. An L9 orthogonal array has been implemented to plan the experiments. It is observed that the control becomes effective for lower area ratios when compared to the higher ones. In addition to this, at high area ratios suction at the base decreases and hence base pressure continuous to diminish with increasing L/D until it reaches a value of L/D=6. The obtained experimental results are subjected to multiple linear regression analysis and Analysis of variance (ANOVA). The performances of the two linear regression models were tested for their prediction accuracy with the help of 15 random test cases. It is observed that, both linear regression models for base pressure without and with control are statistically adequate and capable of making accurate predictions. Furthermore, this work also concludes that, Mach number is the most significant factor affecting base pressure followed by area ratio and L/D ratio for both cases of experimentation. The obtained experimental results are further validated by CFD analysis and are found to be in good concurrence with each other

Base pressure behaviour in a suddenly expanded duct at supersonic mach number regimes using Taguchi design of experiments

Experimental investigations are carried out to study the control of base pressure without and with the use of micro-jets through suddenly expanded axi-symmetric passage in the supersonic regime. Four micro jets having an orifice diameter of 1mm were located at 90◦ intervals. In the base area, active controls jets have been placed on a pitch of a circle diameter that is 1.3 times the exit diameter of the nozzle. The jets were dispensed abruptly into the axi-symmetric tube maintained at a cross-sectional area of 4.84 times the exit nozzle area. The variation of base pressure as a function of flow control parameters namely Mach number, nozzle pressure ratio (NPR) and length to diameter) ratio (L/D) are evaluated experimentally. This study also assesses the impact of flow control variables on base pressure for two cases viz. with control and without control respectively. An L9 orthogonal array of Taguchi and the analysis of variance were employed to investigate the percentage of contribution of these parameters and their interactions affecting the base pressure. The correlations between the various factors affecting the base pressure were obtained by using multiple linear regression equations. Confirmation tests were conducted in order to test the developed linear regression equations for their practical significance. Both the regression models were found to be significant and reliable with a percentage deviation lying in the range of −6.12% to 10.26% for base pressure without control and −13.92% to 6.58% for base pressure with control. Analysis of variance was also performed in order to determine the statistical significance of each parameter on the total variability of base pressure. The study concluded that Mach number is the most influential parameter affecting base pressure followed by NPR and L/D

Modelling of suddenly expanded flow process in supersonic Mach regime using design of experiments and response surface methodology

The present work is an attempt to model, analyze, and control the flow at the base of an abruptly expanded circular duct by using design of experiments (DOE) and response surface methodology (RSM). Tiny-jets in the form of orifice were positioned at an interval of 900, 6.5 mm from the primary axis of the main jet of the nozzle. Experiments were conducted to measure two responses namely, base pressure without the use of micro jets or active control (WoC) and base pressure with the use of micro jets or active control (WC). Mach number (M), nozzle pressure ratio (NPR), area ratio (AR) and length to diameter ratio (L/D) were considered as the input variables (parameters), which control the outputs (i.e. base pressure). Non-linear regression models based on central composite design (CCD) and Box-Behnken design (BBD) have been developed in order to facilitate the input-output relationships. Moreover, the significance of main, square and interaction terms of the developed models have been tested by performing analysis of variance (ANOVA). The ANOVA and significance test results and their respective correlation coefficient values indicate that both the CCD and BBD regression models are statistically adequate for both the base pressure responses of without control and with control respectively. The performances of the nonlinear models have been validated for accuracy prediction by use of 15 test cases. The performance of BBD model is found to be better in forecasting base pressure for both cases of without control and with control when compared to the CCD model

Global burden of 288 causes of death and life expectancy decomposition in 204 countries and territories and 811 subnational locations, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BACKGROUND Regular, detailed reporting on population health by underlying cause of death is fundamental for public health decision making. Cause-specific estimates of mortality and the subsequent effects on life expectancy worldwide are valuable metrics to gauge progress in reducing mortality rates. These estimates are particularly important following large-scale mortality spikes, such as the COVID-19 pandemic. When systematically analysed, mortality rates and life expectancy allow comparisons of the consequences of causes of death globally and over time, providing a nuanced understanding of the effect of these causes on global populations. METHODS The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2021 cause-of-death analysis estimated mortality and years of life lost (YLLs) from 288 causes of death by age-sex-location-year in 204 countries and territories and 811 subnational locations for each year from 1990 until 2021. The analysis used 56 604 data sources, including data from vital registration and verbal autopsy as well as surveys, censuses, surveillance systems, and cancer registries, among others. As with previous GBD rounds, cause-specific death rates for most causes were estimated using the Cause of Death Ensemble model-a modelling tool developed for GBD to assess the out-of-sample predictive validity of different statistical models and covariate permutations and combine those results to produce cause-specific mortality estimates-with alternative strategies adapted to model causes with insufficient data, substantial changes in reporting over the study period, or unusual epidemiology. YLLs were computed as the product of the number of deaths for each cause-age-sex-location-year and the standard life expectancy at each age. As part of the modelling process, uncertainty intervals (UIs) were generated using the 2·5th and 97·5th percentiles from a 1000-draw distribution for each metric. We decomposed life expectancy by cause of death, location, and year to show cause-specific effects on life expectancy from 1990 to 2021. We also used the coefficient of variation and the fraction of population affected by 90% of deaths to highlight concentrations of mortality. Findings are reported in counts and age-standardised rates. Methodological improvements for cause-of-death estimates in GBD 2021 include the expansion of under-5-years age group to include four new age groups, enhanced methods to account for stochastic variation of sparse data, and the inclusion of COVID-19 and other pandemic-related mortality-which includes excess mortality associated with the pandemic, excluding COVID-19, lower respiratory infections, measles, malaria, and pertussis. For this analysis, 199 new country-years of vital registration cause-of-death data, 5 country-years of surveillance data, 21 country-years of verbal autopsy data, and 94 country-years of other data types were added to those used in previous GBD rounds. FINDINGS The leading causes of age-standardised deaths globally were the same in 2019 as they were in 1990; in descending order, these were, ischaemic heart disease, stroke, chronic obstructive pulmonary disease, and lower respiratory infections. In 2021, however, COVID-19 replaced stroke as the second-leading age-standardised cause of death, with 94·0 deaths (95% UI 89·2-100·0) per 100 000 population. The COVID-19 pandemic shifted the rankings of the leading five causes, lowering stroke to the third-leading and chronic obstructive pulmonary disease to the fourth-leading position. In 2021, the highest age-standardised death rates from COVID-19 occurred in sub-Saharan Africa (271·0 deaths [250·1-290·7] per 100 000 population) and Latin America and the Caribbean (195·4 deaths [182·1-211·4] per 100 000 population). The lowest age-standardised death rates from COVID-19 were in the high-income super-region (48·1 deaths [47·4-48·8] per 100 000 population) and southeast Asia, east Asia, and Oceania (23·2 deaths [16·3-37·2] per 100 000 population). Globally, life expectancy steadily improved between 1990 and 2019 for 18 of the 22 investigated causes. Decomposition of global and regional life expectancy showed the positive effect that reductions in deaths from enteric infections, lower respiratory infections, stroke, and neonatal deaths, among others have contributed to improved survival over the study period. However, a net reduction of 1·6 years occurred in global life expectancy between 2019 and 2021, primarily due to increased death rates from COVID-19 and other pandemic-related mortality. Life expectancy was highly variable between super-regions over the study period, with southeast Asia, east Asia, and Oceania gaining 8·3 years (6·7-9·9) overall, while having the smallest reduction in life expectancy due to COVID-19 (0·4 years). The largest reduction in life expectancy due to COVID-19 occurred in Latin America and the Caribbean (3·6 years). Additionally, 53 of the 288 causes of death were highly concentrated in locations with less than 50% of the global population as of 2021, and these causes of death became progressively more concentrated since 1990, when only 44 causes showed this pattern. The concentration phenomenon is discussed heuristically with respect to enteric and lower respiratory infections, malaria, HIV/AIDS, neonatal disorders, tuberculosis, and measles. INTERPRETATION Long-standing gains in life expectancy and reductions in many of the leading causes of death have been disrupted by the COVID-19 pandemic, the adverse effects of which were spread unevenly among populations. Despite the pandemic, there has been continued progress in combatting several notable causes of death, leading to improved global life expectancy over the study period. Each of the seven GBD super-regions showed an overall improvement from 1990 and 2021, obscuring the negative effect in the years of the pandemic. Additionally, our findings regarding regional variation in causes of death driving increases in life expectancy hold clear policy utility. Analyses of shifting mortality trends reveal that several causes, once widespread globally, are now increasingly concentrated geographically. These changes in mortality concentration, alongside further investigation of changing risks, interventions, and relevant policy, present an important opportunity to deepen our understanding of mortality-reduction strategies. Examining patterns in mortality concentration might reveal areas where successful public health interventions have been implemented. Translating these successes to locations where certain causes of death remain entrenched can inform policies that work to improve life expectancy for people everywhere. FUNDING Bill & Melinda Gates Foundation

Experimental investigation on the performance of single spark ignition and twin spark ignition engine fuelled with ethanol-gasoline blends

Increasing the automobile population and contamination of the atmospheric air is a significant threat to the environment. Harmful emissions from the engine exhaust have considerably increased by manifolds. To bring down the pollution rate modern world demands much cleaner combustion with lesser amounts of emissions. Many investigations on IC engines have been conducted to discover such fuels that can efficiently replace the fossil fuels, produce higher heating value, and can burn to produce lesser or no harmful exhaust emissions. Also, a large number of engine modifications are being brought about to attain optimal performance values and reduced exhaust emissions but, the demand for lesser emission is a never-ending one. The investigational iteration for producing a better engine is an unstoppable one and proceeds to the next level with a small improvement in the result. Continuing to investigate in the same direction the current experimental work, investigates the performance characteristics of a single-cylinder engine with a single spark plug ignition and twin spark ignition respectively fuelled with blends of ethanol and gasoline. The experimentation was conducted at the engine’s rated compression ratio. Engine performance characteristics were initially tested by combusting the fuel blends with only one spark plug while cutting off the second one. In the second stage of the experiment, a second spark plug additional to the earlier one was introduced into the combustion chamber. The engine’s performance characteristics were tested under the same compression ratio and with the same blends of ethanol and gasoline fuel, similar to that used in the experimentation with a single spark plug. The experimental investigation demonstrated an improvement in the performance characteristics and also a decrease in the exhaust emissions with ethanol-gasoline blends and twin spark ignition engine

A typology for clients' multi-project environments

Construction management research and practice is dominated by a single project paradigm. This does not reflect the true nature of many construction clients who have large multi-project portfolios. Traditional single project management strategies are usually adopted for managing such portfolios - with limited success. The literature suggests that programmes, within portfolios, require different forms of management in order to optimize project delivery. In order to better understand these portfolios and thereby allow the exploration of new forms of management, a typology has been developed mapping out the various features of client's construction portfolios. The resultant typology provides a simple method for identifying the programme composition of a portfolio, highlighting the expected features of each programme type, and thereby directing management attention to the main aspects of each programme that can be optimized for efficiency. Six cases of client's construction project portfolios were studied using a highly structured, replication logic, case study methodology. A typology of clients' multi-project environments was developed and validated through literal and theoretical replication between cases. Three main types emerged as descriptive of programmes within client's construction portfolios: bounded programmes, target programmes and rolling programmes. The distinctive features of each type suggest that programme-specific approaches may be necessary for the successful delivery of projects within client's construction portfolios.Case studies, multi-projects, portfolio, programmes, typology,

Predictive modeling of suddenly expanded flow process in the Supersonic Mach number regime using response surface methodology

The present work uses design of experiments (DOE) technique along with response surface methodology to develop linear models, to establish linear input-output relationships in a suddenly expanded flow process. Mach number (M), nozzle pressure ratio (NPR), area ratio (AR) and length to diameter (L/D) ratio have been considered as the input parameters, which controls the output (i.e. base pressure). Full factorial DOE has been implemented for developing the linear model. Experiments were conducted to measure base pressure by two means i.e. without control (WoC) and with the use of active control (WC). The adequacy of developed models was checked through statistical analysis. Fifteen random test cases were conducted in order to validate the models. It is observed that, both linear regression models for base pressure without and with control are statistically adequate and capable of making accurate predictions

Investigation of effect of process parameters on suddenly expanded flows through an axi-symmetric nozzle for different Mach numbers using design of experiments

Experiments are conducted to determine base pressure variation through micro-jets from a suddenly expanded axisymmetric passage. Four micro-jets having an orifice diameter of 1mm are situated at 900 interims along the base at 6.5 mm from the geometrical axis of the main jet. The Mach number and L/D ratios were the process parameters employed in the study. The flow stream was extended all of a sudden into an axi-symmetric duct of 4.84 cross-sectional area for all the Mach numbers and L/D ratios respectively. The test Mach numbers used in the study was 2, 2.5 and 3; length-to-diameter ratios selected for the sudden expansion tube were 4, 6 and 8. The jets were operated at an overexpansion level of (Pe/Pa = 0.277). The experiments are conducted as per Taguchi design of experiments. From this investigation, one will be able to identify the enlargement length to diameter ratio resulting in maximum increasing or decreasing base pressure. Mathematical models are also developed for base pressure based on Mach number and L/D ratio with a maximum error of ± 10%

Experimental and numerical studies on flow from axisymmetric nozzle flow with sudden expansion for mach 3.0 using CFD.

Researches over late in the field of aerodynamic vehicles have been concerned with the problem of flow separation over its base which has led to the establishment of low pressure circulation region. This pressure is found to be noticeably lower in comparison with the free stream atmospheric pressure. Base drag due to such pressure differences can be up to two-thirds of the total drag which is primarily dictated by base pressure. The present study aims to conduct experiments in order to study the base pressure variation from an axisymmetric nozzle exit of 10 mm diameter. Area ratio i.e., ratio of area of duct which is suddenly expanded to nozzle exit area considered in this particular study is 4.84. The fundamental control parameters considered in the current study are the nozzle pressure ratio (NPR) and length-to-diameter (L/D) ratio which apparently are termed to be inertial and geometric parameters respectively. The tests have been conducted for NPR’s spanning from 3 to 11 in steps of 2. Accordingly L/D ratio was varied from 10 to 1 where tests were conducted for L/D ratios of 10, 9, 8, 7, 6, 5, 4, 3, 2 and 1. The results revealed that for increase in the NPR values once the flow is attached to the duct, the base pressure steadily decreased. Wall pressure distribution throughout the enlarged duct has also been studied in order to understand the oscillatory flow nature. The present work also proposes an effective numerical model for base pressure by use of Computational Fluid Dynamics (CFD). The numerical model of the axisymmetric nozzle and the enlarged duct was designed using ANSYS Fluent which is the CFD solver and engaged in the present work. Numerical iterations were completed, and specific values for base pressure have been analyzed. The numerical results were found to be in good agreement with the experimental ones

Experimental and numerical studies on flow from axisymmetric nozzle flow with sudden expansion for Mach 3.0 using CFD

Researches over the recent past in the field of aerodynamic vehicles have been concerned with the problem of flow separation over its base which has lead to the formation of low pressure circulation region. This pressure is found to be noticeably lower than the free stream atmospheric pressure. Base drag due to such pressure differences can be up to twothirds of the total drag and is principally dictated by base pressure. The present study aims to conduct experiments in order to study the variation of base pressure from an axisymmetric nozzle exit of 10mm diameter. Area ratio i.e. ratio of area of suddenly expanded duct to nozzle exit area considered in this particular study is 4.84. The fundamental control parameters considered in the study are the nozzle pressure ratio (NPR) and length-to-diameter (L/D) ratio which apparently are the inertia and geometric parameters respectively. The tests are conducted for NPR’s ranging from 3 to 11 in steps of 2. Accordingly L/D ratio was considered from 10 to 1 where tests were conducted for L/D 10, 9, 8, 7, 6, 5, 4, 3, 2 and 1. The results showed that for increase in the NPR values once the flow is attached to the duct, the base pressure progressively decreased. Wall pressure distribution throughout the enlarged duct is also studied to understand the oscillatory nature of flow. This work also proposes an effective numerical model for base pressure using Computational Fluid Dynamics (CFD). The computational/numerical model of the axisymmetric nozzle and the enlarged duct was constructed using ANSYS Fluent which is the CFD solver and employed in the present work. Numerical iterations were completed, and the detailed values for base pressure are analyzed. The numerical results were found to agree well with the experimental ones