The effect of rear cavity modifications on the drag and flow field topology of a Square Back Ahmed Body

2021 ◽  
pp. 095440702199091
Author(s):  
Naveen Koppa Shivanna ◽  
Pritanshu Ranjan ◽  
Shibu Clement
Keyword(s):  
Drag Reduction ◽  
Reference Model ◽  
Lift Coefficient ◽  
Body Height ◽  
Power Spectra ◽  
The Body ◽  
Recirculation Region ◽  
Cavity Depth ◽  
The Mean ◽  
Ahmed Body

This work presents a numerical investigation of turbulent flow over a simplified vehicle model called the Square Back Ahmed Body (SBAB). The simulations are performed at Reynolds number 1 × 105 using the k − [Formula: see text] SSTSAS turbulence model. The numerical results for the standard reference model, that is, SBAB, have been validated against available experimental data and numerical simulations. The performance of a passive flow controller with four variants on the mean wake topology and the resultant drag reduction is evaluated. The four variants are; (i) straight cavity, (ii) straight cavity with rounded edges, (iii) C-shaped cavity, and (iv) tapered cavity. For a straight cavity with a depth equal to 33.33% of the body height, drag is lowered by 5.63%. With the same cavity depth, rounding the straight cavity edges reduces the drag by 10.67% owing to the streamlining and shortening of the recirculation region. For a C-shaped cavity, the amount of drag reduction increased slightly by 1% more than that off straight cavity with rounded edges, due to improvement in the base pressure distribution compared to that of the latter case. Tapering the cavity edges at an angle of 6° gave a significant drag reduction of 22.55% primarily due to a tremendous decrease in wake size. The drag reduction achieved in all the cases results from the modification in the mean wake topology induced by afterbody shape remodeling. The power spectra of the evolution of the lift coefficient over time reveal a noticeable decrement in the flow randomness with the inclusion of a cavity and its modifications, which interprets the mitigation of the chaotic nature in the wake. The cavity presence has also increased the vorticity spreading rate in the mixing layer and produced significant attenuation of Turbulent Kinetic Energy (TKE).

Numerical Investigation of a Square Back Vehicle Equipped With a Single Cavity and Multi-Cavity

2020 ◽  
Author(s):  
Naveen Koppa Shivanna ◽  
Pritanshu Ranjan ◽  
Shibu Clement
Keyword(s):  
Drag Reduction ◽  
Numerical Investigation ◽  
Bluff Body ◽  
Body Height ◽  
The Body ◽  
Vehicle Model ◽  
Cavity Depth ◽  
Passive Flow ◽  
The Mean ◽  
Single Cavity

Abstract This work aims to investigate the comparative effect of two passive flow controls in modifying the mean wake topology around a simplified square back vehicle model. The two passive flow controls are (i) Single cavity and (ii) Multi-cavity. A straight cavity with an optimum depth at the rear base of a vehicle is a well-known technique used to alter the mean wake topology and achieve drag reduction[1]. For two dimensional bluff bodies, a multi-cavity is known to deliver better drag reduction at shorter cavity depths in comparison to a single cavity[2]. With this viewpoint, a numerical investigation is carried out to examine the performance of a multi-cavity over a single cavity in drag reduction for a three-dimensional bluff body vehicle model. The numerical simulations are performed at Reynolds Number (Re) = 1 × 105 using the k-ω SSTSAS turbulence model in a Finite volume open-source code OpenFOAM. The investigations revealed, for any cavity depth, a single cavity always performed better than multi-cavity in reducing drag. However, at optimum cavity depth equal to 33% of the body height, the drag reduction magnitude was identical for both the flow controls. The plausible mechanisms responsible for their relative difference in performance will be explored by analyzing the base pressure distribution, wake mean topology, and the temporal behavior of the wake.

A numerical investigation of the asymmetric wake mode of a squareback Ahmed body – effect of a base cavity

2017 ◽  
Vol 831 ◽  
pp. 675-697 ◽  
Author(s):  
J.-M. Lucas ◽  
O. Cadot ◽  
V. Herbert ◽  
S. Parpais ◽  
J. Délery
Keyword(s):  
Drag Reduction ◽  
Body Height ◽  
Power Spectra ◽  
Low Pressure ◽  
The Body ◽  
Frequency Resolution ◽  
Recirculation Region ◽  
Periodic Mode ◽  
Lateral Velocity ◽  
Base Cavity

Numerical simulations of the turbulent flow over the flat backed Ahmed model at Reynolds number $Re\simeq 4\times 10^{5}$ are conducted using a lattice Boltzmann solver to clarify the mean topology of the static symmetry-breaking mode of the wake. It is shown that the recirculation region is occupied by a skewed low pressure torus, whose part closest to the body is responsible for an extra low pressure imprint on the base. Shedding of one-sided vortex loops is also reported, indicating global quasi-periodic dynamics in conformity with the seminal work of Grandemange et al. (J. Fluid Mech., vol. 722, 2013, pp. 51–84). Despite the limited low frequency resolution of the simulation, power spectra of the lateral velocity fluctuations at different locations corroborate the presence of this quasi-periodic mode at a Strouhal number of $St=0.16\pm 0.03$. A shallow base cavity of $5\,\%$ of the body height reduces the drag coefficient by $3\,\%$ but keeps the recirculating torus and its interaction with the base mostly unchanged. The drag reduction lies in a global constant positive shift of the base pressure distribution. For a deep base cavity of $33\,\%$ of the body height, a drag reduction of $9.5\,\%$ is obtained. It is accompanied by a large elongation of the recirculation inside the cavity that considerably attenuates the low pressure sources therein together with a symmetrization of the low pressure torus. The global quasi-periodic mode is found to be inhibited by the cavity.

scholarly journals Prediksi Tinggi Badan Ditentukan dari Panjang Rentang Lengan dan Panjang Telapak Kaki Pada Mongoloid Feminina Khususnya Etnis Jawa

2018 ◽  
Vol 2 (2) ◽  
Author(s):  
Nur Mujaddidah Mochtar
Keyword(s):  
Clinical Medicine ◽  
Pearson Correlation ◽  
Body Height ◽  
Regression Equation ◽  
The Body ◽  
Regression Equations ◽  
Foot Length ◽  
Arm Span ◽  
Knee Height ◽  
The Mean

Background: There are various circumstances where measurements are not actually possible, replacement parameters can be used to estimate body height. Many characteristics of body height measurement and how to measure it. These include anthropometric measurements that can be used for the identification of medicolegal-forensic processes. Body height in clinical medicine and in the field of scientific research can be easily estimated using various anthropometric parameters such as arm span, knee height, foot length and foot breadth, and others. The arm span and foot length has proved to be one of the most reliable predictors. This study was conducted to estimate of body height from arm span and foot length using the regression equation and to determine the correlation between the body height and arm span and foot length.Methods: This study was conducted at Universitas Muhammadiyah Surabaya with 182 Javanese female students. Stature, arm span and foot length measured directly using anthropometric technique and measuring tape. The data obtained were then analyzed with SPSS version 16. The regression equation was derived for the estimate of body height and the relationship between stature, arm span and foot length determined by the Pearson correlation.               Results: We found that the mean body height of Javanese women was 1534,45 ± 47,623  mm, mean of arm span 1543,25 ± 60,468 mm and the mean of foot length 226,14 ± 9,586 mm. The correlation between stature and arm span was positive and significant (r = 0,715  , p <0,05). The correlation between stature and foot length was positive and significant (r = 0,726 , p <0,05). The correlation between stature and arm span and foot length was positive and significant (r = 0,798, p <0,05).               Conclusion: Body height correlates well with the arm span and foot length so that it can be used as a reliable marker for high estimates using regression equations.

scholarly journals Internal Proportions of The Body Composition in Members of the Female National Tennis Team of Poland

2018 ◽  
Vol 2 (73) ◽  
Author(s):  
Marina Jagiello ◽  
Wladislaw Jagiello
Keyword(s):  
Body Composition ◽  
Body Size ◽  
Body Mass ◽  
Body Height ◽  
The Body ◽  
Control Group ◽  
Tennis Players ◽  
National Team ◽  
The Mean ◽  
Total Body

Contemporary anthropological research confirms the fact that body composition is one of the basic elements differentiating athletes from persons not practising sport. Among athletes representing various branches of sport there are also significant differences in their body composition. Internal proportions of the body composition of an athlete, or a selected group of athletes, is an especially important yet little researched issue of sports anthropology. This problem is still topical in sports games, especially in tennis. Therefore, the aim of the study was to determine internal proportions of the body composition of female tennis players from the Polish national team in comparison to persons who do not practice sport professionally. The study involved female athletes of the Polish national tennis team (n = 10). The study was carried out in a training camp from 28 September to 9 October 2002 in Zakopane — Centre of Sports Preparation. Athletes’ age was 16—20 (18.1 ± 1.4) years, and the training experience 8—12 years (10.5 ± 1.8). The mean body height for the group members was 171.9 ± 6.7 cm and the mean body mass 59.7 ± 6.3 kg. The results of research by Piechaczek et al. (1996) constituted the reference point for the results of measurements of Polish tennis representatives. The authors studied 153 female students of Warsaw Technical University aged 20.2 ± 1.09 years. They were randomly chosen students of the first and the second year of various departments at this university. The mean body height of the students was 166.2 ± 6.2 cm and the mean body mass 57.4 ± 7.72 kg. Anthropometric measurements were taken using standard instruments (Drozdowski, 1998). The analysis involved 11 somatic features which determined three so-called factors of body composition: length (m1), stoutness (m2) and obesity (m3). The assessment of proportions of the body composition was made by means of Perkal’s natural indices (1953) with Milicerowa’s modifications (1956). We determined the following: composition factors (m), index of total body size (M), internal proportions of the body composition, evenness of composition, the code of internal proportions; also the assessment of internal proportions of the body composition within each of the factors.Taking into consideration the mean values of the studied somatic features in the control group and the comparative group we found differences in their body composition. The representatives of the Polish national tennis team showed substantially longer upper and lower limbs, and the body height was greater. They also had much greater forearm perimeter and shorter pelvic width. As to the total body size, the tennis players slightly exceeded the students (M = 0.24). The total body size (M) resulted from high values of length features (m1 = 1.01), low ones of stoutness (m2 = –0.39) and medium ones of obesity (m3 = 0.1). The value of the intragroup variability index (harmony of composition) amounted to 1.4 and the code of internal proportions of tennis players’ body composition — to 6—2—4. The proportions of internal features of the stoutness index (natural indices of features within a factor) showed the advantage of the forearm perimeter (1.62) and elbow width (0.36). The knee width (–1.30) and pelvic width (–0.60) were disproportionate to the total value of this factor. The input of features characterizing the length factor was relatively proportional.Keywords: tennis, training, body composition, internal proportions.

scholarly journals Age relative height, weight and body mass index percentiles of children in Jos, North-Central Nigeria

2021 ◽  
Vol 12 (8) ◽  
pp. 149-154
Author(s):  
Ovayoza O. Mosugu ◽  
Francis Shinku ◽  
Jacob C. Nyam ◽  
Emmanuel S. Mador
Keyword(s):  
Body Mass Index ◽  
Childhood Obesity ◽  
Body Mass ◽  
Weight Status ◽  
Body Height ◽  
Mean Value ◽  
The Body ◽  
Healthy Weight ◽  
North Central ◽  
The Mean

Background: Interpretation of body mass index in children is quite different from that in adults which use standard weight status categories that are the same for all ages and for both men and women. Aims and Objective: The study was aimed at determining the prevalence of childhood obesity in Jos. Materials and Methods: A total of 371 children were enrolled in the study. Weight was taken with only light clothing and without foot wears. Height obtained without head-gears or shoes and the measuring flat tops pressed down to avoid errors due to tall hair. Body mass index were calculated for each subject as ratio of body weight to body height. All data were analyzed statistically and separately for different ages and the mean values for height against age, weight against age, height against weight and BMI for age was obtained with centiles of absolute deviations from the mean. Results: The age of the studied population ranged from 3 – 14 years with mean of 8.4 ± 2.8. Height of the children on the other hand ranged from 0.9 – 1.64 meters with mean value of 1.26 ± 0.15 and their weight ranged from 10 – 76 kg with mean value of 25.6 ± 9.2. Out of the 371 children studied, 14 (3.8%) were found to be underweight, 302 (81.4%) had healthy weight while 41 (11%) were at risk of overweight and 14 (3.8%) were overweight. In addition, the body mass index of girls was found to be significantly higher than those of boys at 12 and 13 years only. Conclusion: It is concluded that the prevalence of childhood obesity is high in Jos, North-central Nigeria.

scholarly journals The Effects of Aerodynamic Interference on the Aerodynamic Characteristics of a Twin-Box Girder

2021 ◽  
Vol 11 (20) ◽  
pp. 9517
Author(s):  
Buchen Wu ◽  
Geng Xue ◽  
Jie Feng ◽  
Shujin Laima
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Body Height ◽  
Flow Characteristics ◽  
Aerodynamic Characteristics ◽  
The Body ◽  
Incoming Flow ◽  
Aerodynamic Forces ◽  
Box Girder ◽  
The Mean

To investigate the aerodynamic characteristics of a twin-box girder in turbulent incoming flow, we carried out wind tunnel tests, including two aerodynamic interferences: leading body-height grid, and leading circular cylinder. In this study, the pressure distribution and the mean and fluctuating aerodynamic forces with the two interferences are compared with bare deck in detail to investigate the relationship between aerodynamic characteristics and the incoming flow characteristics (including Reynolds number and turbulence intensity). The experimental results reveal that, owing to the body-height flow characteristics around the deck interfered with by the body-height grid, the disturbed aerodynamic characteristics of the twin-box girder differ considerably from those of the bare twin-box girder. At the upstream girder, due to the vortex emerging from the body-height grid breaking the separation bubble, pressure plateaus in the upper and lower surface are eliminated. In addition, the turbulence generated by the body-height grid reduces the Reynolds number sensitivity of the twin-box girder. At a relatively high Reynolds number, the fluctuating forces are mainly dominated by turbulence intensity, and the time-averaged forces show almost no change under high turbulence intensity. At a low Reynolds number, the time-averaged forces change significantly with the turbulence intensity. Moreover, at a low Reynolds number, the wake of the leading cylinder effectively forces the boundary layer to transition to turbulence, which reduces the Reynolds number sensitivity of the mean aerodynamic forces and breaks the separation bubbles. Additionally, the fluctuating drag force and the fluctuating lift force are insensitive to the diameter and the spacing ratio.

scholarly journals Bluff bodies in deep turbulent boundary layers: Reynolds-number issues

2007 ◽  
Vol 571 ◽  
pp. 97-118 ◽  
Author(s):  
HEE CHANG LIM ◽  
IAN P. CASTRO ◽  
ROGER P. HOXEY
Keyword(s):  
Reynolds Number ◽  
Boundary Layers ◽  
Delta Wing ◽  
Body Height ◽  
Turbulent Boundary Layers ◽  
The Body ◽  
Bluff Bodies ◽  
Mean Flow ◽  
Order Of Magnitude ◽  
The Mean

It is generally assumed that flows around wall-mounted sharp-edged bluff bodies submerged in thick turbulent boundary layers are essentially independent of the Reynolds number Re, provided that this exceeds some (2–3) × 104. (Re is based on the body height and upstream velocity at that height.) This is a particularization of the general principle of Reynolds-number similarity and it has important implications, most notably that it allows model scale testing in wind tunnels of, for example, atmospheric flows around buildings. A significant part of the literature on wind engineering thus describes work which implicitly rests on the validity of this assumption. This paper presents new wind-tunnel data obtained in the ‘classical’ case of thick fully turbulent boundary-layer flow over a surface-mounted cube, covering an Re range of well over an order of magnitude (that is, a factor of 22). The results are also compared with new field data, providing a further order of magnitude increase in Re. It is demonstrated that if on the one hand the flow around the obstacle does not contain strong concentrated-vortex motions (like the delta-wing-type motions present for a cube oriented at 45° to the oncoming flow), Re effects only appear on fluctuating quantities such as the r.m.s. fluctuating surface pressures. If, on the other hand, the flow is characterized by the presence of such vortex motions, Re effects are significant even on mean-flow quantities such as the mean surface pressures or the mean velocities near the surfaces. It is thus concluded that although, in certain circumstances and for some quantities, the Reynolds-number-independency assumption is valid, there are other important quantities and circumstances for which it is not.

Selected Parameters of Anaerobic Fitness and Somatic Components Among Super-league Team Handballers Playing Various Positions

2020 ◽  
Vol 30 (92) ◽  
pp. 41-46
Author(s):  
Krzysztof Krawczyk
Keyword(s):  
Body Composition ◽  
Test Procedure ◽  
Body Height ◽  
Cycle Ergometer ◽  
Mean Value ◽  
Wingate Test ◽  
The Body ◽  
Composition Material ◽  
The Mean ◽  
Super League

Study aim: The aim of the study was to evaluate the relative mechanical work (J/kg), maximal power (W/kg) and the time to attain (s) and of maintaining (s) power in the Wingate test among super-league handballers playing different positions. Additionally, the somatic components of the body were assessed, based on measuring body composition. Material and methods: Participants: 20 players of the super-league handball team. Mean age of the subjects - 25.84 ± 3.36 years, mean body height - 191.89 ± 12.82 cm, mean body mass - 97.99 ± 7.18 kg, mean BMI - 25.85 ± 1.91. Anaerobic fitness was assessed in accordance via the Wingate-30 s test procedure, on a Monark 824E cycle ergometer, using the MCEv5.0 software program, while body composition was assessed with the Tanita SC 330, Japan body composition analyser. Results: The mean value of the maximum power among the participants was - 11.45 ± 0.86 W/kg., mean value of the work - 256.78 ± 15.93 J/kg., the mean value of the time to attain power - 4.63 ± 0.80 s., mean value of time maintaining power - 2.91 ± 1.05 s., power decrease index - 26.17 ± 3.52%. The mean value of the FAT% index - 12.92 ± 3.27% and the mean percentage of water in the body composition - TBW% - 60.94 ± 1.99. Conclusions: The selected parameters of anaerobic fitness obtained by the participants in the Wingate test were at a good and average level, which certainly did not guarantee the achievement of high sports results in the men's handball super-league competition. Higher values of the parameters regarding anaerobic fitness were obtained by the players playing in the positions: centre and winger, relative to pivots and goalkeepers. The values of body composition tissue components were within the limits of the results for referencing.

SECULAR CHANGES IN HEIGHT, BODY WEIGHT, BODY MASS INDEX AND PUBERTAL DEVELOPMENT IN MALE CHILDREN AND ADOLESCENTS IN KRAKOW, POLAND

2011 ◽  
Vol 44 (4) ◽  
pp. 495-507 ◽  
Author(s):  
ŁUKASZ KRYST ◽  
MAŁGORZATA KOWAL ◽  
AGNIESZKA WORONKOWICZ ◽  
JAN SOBIECKI ◽  
BARBARA ANNA CICHOCKA
Keyword(s):  
Body Mass Index ◽  
Body Weight ◽  
Children And Adolescents ◽  
Body Mass ◽  
Pubertal Development ◽  
Body Height ◽  
The Body ◽  
Secular Changes ◽  
The Past ◽  
The Mean

SummaryThis study examined the secular changes in height, body weight, body mass index and pubertal development in male children and adolescents in Krakow (Poland) over the past 80 years, with an emphasis on the last decade (2000–2010). The survey of the population of Krakow is a continuation of observations conducted in that area for many years. The analysis aims to determine whether in the last decade Krakow still witnessed the secular trend, and what form the trend took. The body height and weight, and body mass index (BMI), of 1862 boys aged 3.5–18.5 years were analysed, against the background of a survey series from the years 1938 (N=1801), 1971 (N=2045), 1983 (N=3124) and 2000 (N=2328). The mean body height, in almost all age categories, was greater than in the past; however the final height over the last decade remained the same. The mean values of body weight and BMI increased, especially in the last decade. Also, an acceleration of puberty in boys was observed. The last 10 years saw an over 3-month decrease in the age of initial appearance of pubic hair in boys. In conclusion, the last decade saw cessation of the growing taller trend: maximum body height stabilized at approximately 179 cm, but weight and BMI increased. Also, a distinct acceleration of puberty was noticed. Lack of height increase, at the same time as weight gain and puberty acceleration, indicate a progressing developmental disharmony.

scholarly journals Shortness: an unknown phenotype of multiple endocrine neoplasia type 1

2013 ◽  
Vol 169 (1) ◽  
pp. 133-137
Author(s):  
Caroline L López ◽  
Peter Langer ◽  
Jens Waldmann ◽  
Volker Fendrich ◽  
Helmut Sitter ◽  
...  
Keyword(s):  
Multiple Endocrine Neoplasia ◽  
Multiple Endocrine Neoplasia Type ◽  
Body Height ◽  
The Body ◽  
Female Population ◽  
Endocrine Neoplasia ◽  
Endocrine Neoplasia Type ◽  
Phenotype Characteristic ◽  
The Mean

ObjectiveAn observation of shortness among the female participants of a regular screening program in multiple endocrine neoplasia type 1 (MEN1) patients has raised the question as to whether shortness represents a phenotype characteristic of the disease.MethodsThe body height (cm) of genetically confirmed MEN1 patients at the time of diagnosis was compared with the body height of their unaffected relatives (parents, siblings, and children), the mid-parental body height, and the body height of the age-matched German population. Univariate analysis of the clinical variables was performed using the t-test, Mann–Whitney U test, and ANOVA as appropriate, and multivariate analysis was performed as a logistic regression analysis. P values <0.05 were considered statistically significant.ResultsThe mean body height of 22 female MEN1 patients (mean age 33.5 years) was 161±5 cm and thus significantly lesser than the body heights of their unaffected female relatives (mean 165.5±7.3 cm, P=0.027) and the age-matched German female population (mean 167 cm, P=0.0001) and mid-parental height (177.5 cm, P<0.0001). The mean body height of 24 male MEN1 patients (mean age 34.8 years) was also lesser (177±6.5 cm) than the average body height of German males in this age group (180 cm, P=0.031) and tended to be lesser than that of their unaffected male relatives (178.5±5.8 cm, P=0.0915) and the mid-parental body height (177.5 cm, P=0.124).ConclusionsSmall body height is a yet unrecognized phenotype characteristic of MEN1 patients, especially in women. The mechanisms behind this phenotypical characteristic warrant further investigation.

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