Analysis of two-equation turbulence models for recirculating flows

The two-equation kappa-epsilon model is used to analyze turbulent separated flow past a backward-facing step. It is shown that if the model constraints are modified to be consistent with the accepted energy decay rate for isotropic turbulence, the dominant features of the flow field, namely the size of the separation bubble and the streamwise component of the mean velocity, can be accurately predicted. In addition, except in the vicinity of the step, very good predictions for the turbulent shear stress, the wall pressure, and the wall shear stress are obtained. The model is also shown to provide good predictions for the turbulence intensity in the region downstream of the reattachment point. Estimated long time growth rates for the turbulent kinetic energy and dissipation rate of homogeneous shear flow are utilized to develop an optimal set of constants for the two equation kappa-epsilon model. The physical implications of the model performance are also discussed

Turbulent separated flow past a backward-facing step: A critical evaluation of two-equation turbulence models

The ability of two-equation models to accurately predict separated flows is analyzed from a combined theoretical and computational standpoint. Turbulent flow past a backward facing step is chosen as a test case in an effort to resolve the variety of conflicting results that were published during the past decade concerning the performance of two-equation models. It is found that the errors in the reported predictions of the k-epsilon model have two major origins: (1) numerical problems arising from inadequate resolution, and (2) inaccurate predictions for normal Reynolds stress differences arising from the use of an isotropic eddy viscosity. Inadequacies in near wall modelling play a substantially smaller role. Detailed calculations are presented which strongly indicate the standard k-epsilon model - when modified with an independently calibrated anisotropic eddy viscosity - can yield surprisingly good predictions for the backstep problem

Analysis of an RNG based turbulence model for separated flows

A two-equation turbulence model of the K-epsilon type was recently derived by using Renormalization Group (RNG) methods. It was later reported that this RNG based model yields substantially better predictions than the standard K-epsilon model for turbulent flow over a backward facing step - a standard test case used to benchmark the performance of turbulence models in separated flows. The improvements obtained from the RNG K-epsilon model were attributed to the better treatment of near wall turbulence effects. In contrast to these earlier claims, it is shown in this paper that the original version of the RNG K-epsilon model substantially underpredicts the reattachment point in the backstep problem. This is a deficiency that is traced to the modeling of the production of dissipation term. However, with the most recent improvements in the RNG K-epsilon model, excellent results for the backstep problem are now obtained

Application of a new K-tau model to near wall turbulent flows

A recently developed K-tau model for near wall turbulent flows is applied to two severe test cases. The turbulent flows considered include the incompressible flat plate boundary layer with the adverse pressure gradients and incompressible flow past a backward facing step. Calculations are performed for this two-equation model using an anisotropic as well as isotropic eddy-viscosity. The model predictions are shown to compare quite favorably with experimental data

Development of turbulence models for shear flows by a double expansion technique

Turbulence models are developed by supplementing the renormalization group (RNG) approach of Yakhot and Orszag with scale expansions for the Reynolds stress and production of dissipation terms. The additional expansion parameter (eta) is the ratio of the turbulent to mean strain time scale. While low-order expansions appear to provide an adequate description of the Reynolds stress, no finite truncation of the expansion for the production of dissipation term in powers of eta suffices - terms of all orders must be retained. Based on these ideas, a new two-equation model and Reynolds stress transport model are developed for turbulent shear flows. The models are tested for homogeneous shear flow and flow over a backward facing step. Comparisons between the model predictions and experimental data are excellent

Development of a recursion RNG-based turbulence model

Reynolds stress closure models based on the recursion renormalization group theory are developed for the prediction of turbulent separated flows. The proposed model uses a finite wavenumber truncation scheme to account for the spectral distribution of energy. In particular, the model incorporates effects of both local and nonlocal interactions. The nonlocal interactions are shown to yield a contribution identical to that from the epsilon-renormalization group (RNG), while the local interactions introduce higher order dispersive effects. A formal analysis of the model is presented and its ability to accurately predict separated flows is analyzed from a combined theoretical and computational stand point. Turbulent flow past a backward facing step is chosen as a test case and the results obtained based on detailed computations demonstrate that the proposed recursion -RNG model with finite cut-off wavenumber can yield very good predictions for the backstep problem

Studies on Fruit Development in Pink and White types of Wax Apple (Syzygium samarangense Merr. & Perry) in Goa, India

Fruit development studies were taken up in white and pink types of wax apple trees aging twelve years old at Goa, India. The study was initiated with the onset of flowering in November during the year 2018. After tagging the flowers on anthesis, samples were drawn periodically to record parameters like fruit weight, fruit volume, fruit length and diameter (upper, middle and lower), quality or biochemical parameters like total acids and sugars. Relative growth rate (RGR) was calculated for all parameters and graphs were generated. In both the types, fruit weight, fruit volume, fruit length and diameter increased in a sigmoidal pattern. The quality characters like TSS, total acids and total sugars also showed a sigmoidal pattern of increase whereas the increase in reducing sugars exhibited a double sigmoidal pattern of increase. It was evident from the curves that there was pronounced peak in growth rate between 21 and 28 days after anthesis for fruit weight, fruit volume, fruit length and diameter, in both pink and white types of wax apple

Evaluation of Different Cultivars of Tuberose (Polianthes tuberosa L.) under Humid agro Climatic conditions of Goa

Tuberose (Polianthes tuberosa L.) is one of the most important tropical bulbous-ornamental cultivated for production of long-lasting flowers spikes. Adaptation and acclimatization of different cultivars under humid agro-climatic conditions of Goa are to be confirmed for their better performance. The present investigation was conducted to evaluate the performance of tuberose cultivars under agro-climatic conditions of Goa during 2014- 2017. Five single and six double cultivars of tuberose were evaluated during the study period. All the cultivars differed in their growth and flowering behaviour. Among the single cultivars, evaluated, maximum number of florets per spike (47.00) was observed in Pune local whereas spike-length (75.59 cm) was maximum in Mexican Single. Among the double cultivars, evaluated, maximum plant height (52.21 cm) and maximum number of leaves per plant (59.63) were recorded with cultivar Arka Suvasini. Leaf length was significantly higher (52.93 cm) in Pearl double whereas leaf width (2.04 cm) was maximum in Calcutta Double. Days to appearance of flower spike were earlier in Arka Suvasini. Minimum days taken for opening of basal floret (84.88 days) were recorded with cultivar Arka Suvasini. Spike girth (0.68 cm), Spike fresh-weight (69.06 cm), floret stalk-length (3.6 cm), floret diameter (5.24 cm), weight of individual floret (3.49 g) and vase life (7.93 days) was significantly maximum in Cv. Arka Suvasini followed by Pearl Double. Based on the performance evaluation cv. Mexican Single among single types and cv. Arka Suvasini and Pearl Double among double types could be recommended for commercial cultivation under agro climatic conditions of Goa

Pregnancy outcome among gestational diabetes mellitus patients in a tertiary care centre

Background: Gestational diabetes mellitus poses numerous health problems for both mother and the fetus. Even though there are improved outcomes, complications of gestational diabetes still persists. Objectives of this study was to find out the maternal and perinatal outcomes in gestational diabetes mellitus.Methods: This study was done among pregnant women attending antenatal outpatient department at Sree Mookambika Institute of Medical Sciences, Kulasekharam. oral glucose tolerance test was done at between 24 to 28 weeks and the values more than their cutoff was labelled as gestational diabetes and their outcome was measured as complications during antenatal period, mode of delivery and perinatal outcome in view of neonatal intensive care unit admissions due to hyperbilirubinemia and respiratory distress syndrome.Results: Out of 500 antenatal mothers 65 were found to have gestational diabetes which is approximately 13%. Obstetric outcomes were 10% of them developed pregnancy induced hypertension, 12% of them ended in preterm labour and polyhydramnios in 2%. Delivery by caesarean section and vaginal route is almost similar. Maximum number of neonatal intensive care admissions are due to hyperbilirubinemia followed by respiratory distress.Conclusions: Screening for gestational diabetes and adequate glycemic control is necessary in preventing short term and long-term complications

Mullerian duct cyst mimicking cervical elongation

Diagnosis of Mullerian duct cyst is determined by histopathological examination. Describe a case of a mass descending per vaginum in a 28-year-old lady that was originally misdiagnosed as an elongation of the cervix's anterior lip. Under anaesthesia, carried out surgical intervention that included complete excision of the mass via a vaginal route.  Pathology result confirmed a benign Mullerian cyst histologically bordered by a single layer of ciliated columnar epithelial cells.