Physical modeling and correlation of separation length in hypersonic laminar ramp flows

2020 ◽  
Author(s):  
Fang Fang ◽  
Xian-Dong Li ◽  
Lin Bao
Keyword(s):  
Boundary Layer ◽  
Physical Modeling ◽  
Analytical Formula ◽  
Boundary Layer Separation ◽  
Laminar Flows ◽  
Incoming Flow ◽  
Flow Conditions ◽  
Key Factors ◽  
Factors Influencing ◽  
New Correlation

To predict the separation length in hypersonic laminar flows over a ramp, the concepts of disturbance strength and anti-disturbance strength are introduced to characterize the key factors influencing boundary layer separation. It is found that the separation length is controlled by a normalized disturbance strength. Based on that, an analytical formula is derived to correlate the separation length with incoming flow conditions and ramp angle, which can predict the location of the separation under various flow and geometry conditions. The new correlation is compared to numerical simulations and experiments as well as the correlations in previous studies, confirming the suitability and effectiveness of the present analysis.

scholarly journals Aerodynamics of airfoil moving along a circular trajectory

2021 ◽  
Vol 2119 (1) ◽  
pp. 012154
Author(s):  
D M Bozheeva ◽  
D A Dekterev ◽  
Ar A Dekterev ◽  
A A Dekterev ◽  
D V Platonov
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Computational Study ◽  
Stationary Flow ◽  
Boundary Layer Separation ◽  
Velocity Fields ◽  
Incoming Flow ◽  
Calculation Methods ◽  
Circular Trajectory ◽  
Qualitative Comparison

Abstract An experimental and computational study of the NACA0016 airfoil has been carried out for two cases: a stationary airfoil in an incoming flow on an aerodynamic stand and an airfoil moving along a circular trajectory in a stationary flow in a hydrodynamic stand. The Reynolds number for both cases was 60000. A qualitative comparison of the velocity fields for the cases with smooth airflow and boundary layer separation was carried out. It is shown that the used calculation methods describe the task under study with sufficient quality.

Autogenous Suction to Prevent Laminar Boundary-Layer Separation

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Hediye Atik ◽  
Leon van Dommelen
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Laminar Flows ◽  
Computational Techniques ◽  
Pressure Gradients ◽  
Practical Application ◽  
Theoretical Limit ◽  
Local Pressure ◽  
Layer Separation ◽  
Straightforward Application

Boundary-layer separation can be prevented or delayed by sucking part of the boundary layer into the surface, but in a straightforward application the required hydraulics entail significant penalties in terms of weight and cost. By means of computational techniques, this paper explores the possibility of autogenous suction, in which the local pressure differences that lead to separation drive the suction used to prevent it. The chosen examples include steady and unsteady laminar flows around leading edges of thin airfoils. No fundamental theoretical limit to autogenous suction was found in the range of angles of attack that could be studied, but rapidly increasing suction volumes suggest that practical application will become increasingly difficult for more severe adverse pressure gradients.

Separation control and drag reduction for boat-tailed axisymmetric bodies through contoured transverse grooves

2017 ◽  
Vol 832 ◽  
pp. 514-549 ◽  
Author(s):  
A. Mariotti ◽  
G. Buresti ◽  
G. Gaggini ◽  
M. V. Salvetti
Keyword(s):  
Boundary Layer ◽  
Passive Control ◽  
Control Method ◽  
Boundary Layer Separation ◽  
Separation Control ◽  
Geometrical Parameters ◽  
Dynamical Structure ◽  
Incoming Flow ◽  
Layer Separation ◽  
Transverse Grooves

We describe the results of a numerical and experimental investigation aimed at assessing the performance of a control method to delay boundary layer separation consisting of the introduction on the surface of contoured transverse grooves, i.e. of small cavities with an appropriate shape orientated transverse to the incoming flow. The shape of the grooves and their depth – which must be significantly smaller than the thickness of the incoming boundary layer – are chosen so that the flow recirculations present within the grooves are steady and stable. This passive control strategy is applied to an axisymmetric bluff body with various rear boat tails, which are characterized by different degrees of flow separation. Variational multiscale large eddy simulations and wind tunnel tests are carried out. The Reynolds number, for both experiments and simulations, is $Re=u_{\infty }D/\unicode[STIX]{x1D708}=9.6\times 10^{4}$; due to the different incoming flow turbulence level, the boundary layer conditions before the boat tails are fully developed turbulent in the experiments and transitional in the simulations. In all cases, the introduction of one single axisymmetric groove in the lateral surface of the boat tails produces significant delay of the boundary layer separation, with consequent reduction of the pressure drag. Nonetheless, the wake dynamical structure remains qualitatively similar to the one typical of a blunt-based axisymmetric body, with quantitative variations that are consistent with the reduction in wake width caused by boat tailing and by the grooves. A few supplementary simulations show that the effect of the grooves is also robust to the variation of the geometrical parameters defining their shape. All the obtained data support the interpretation that the relaxation of the no-slip boundary condition for the flow surrounding the recirculation regions, with an appreciable velocity along their borders, is the physical mechanism responsible for the effectiveness of the present separation-control method.

Mixed Convection on a Vertical Flat Plate With Transition and Separation

1990 ◽  
Vol 112 (1) ◽  
pp. 144-150 ◽  
Author(s):  
T. Cebeci ◽  
D. Broniewski ◽  
C. Joubert ◽  
O. Kural
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Stability Theory ◽  
Separation Bubble ◽  
Boundary Layer Separation ◽  
Laminar Flows ◽  
Linear Stability Theory ◽  
Boundary Layer Equations ◽  
Heating And Cooling ◽  
Vertical Flat Plate

A numerical method has been developed and used to calculate the flow properties of laminar, transitional, and turbulent boundary layers on a vertical flat plate with heat transfer. The governing boundary-layer equations include a buoyancy-force term and are solved by a two-point finite-difference method due to Keller and results obtained for heating and cooling and, in the case of the laminar flows, for an isothermal surface corresponding to that of Merkin. Cooled plates with unheated sections can give rise to boundary-layer separation and reattachment and, on occasions, transition can occur within the separation bubble. Flows of this type have been examined with the inviscid-viscous interaction procedure developed by Cebeci and Stewartson and the location of transition obtained by the en method based on the linear stability theory for air with Pr = 1. Results are given in dimensionless form as a function of Reynolds number, Richardson number, and Prandtl number and quantify those parameters that give rise to separation. Consequences of the use of interaction and stability theory are examined in detail.

Consumers‟ Acceptance of „Halal‟ Credit Card Services: An Empirical Analysis

2015 ◽  
Vol 3 (1) ◽  
pp. 51 ◽  
Author(s):  
Zaimy Johana Johan ◽  
Lennora Putit
Keyword(s):  
Perceived Control ◽  
Credit Card ◽  
Credit Cards ◽  
Product Knowledge ◽  
Key Factors ◽  
Developing Nation ◽  
Business Transactions ◽  
Factors Influencing ◽  
Financial Credit ◽  
Survey Questionnaires

Many past researches have been carried out in an attempt to continuously understand individuals‟ consumption behaviour. This study was conducted to investigate key factors influencing consumers‟ potential acceptance of halal (or permissible) financial credit card services. Specifically, it anticipated the influence of attitude, social influences and perceived control on consumers‟ behavioural intention to accept such services. In addition, factors such as religiosity and product knowledge were also postulated to affect consumers‟ attitude towards the act of using halal credit cards for any retail or business transactions. Using non-probability sampling approach, a total of 500 survey questionnaires was distributed to targeted respondents in a developing nation but only 220 usable feedbacks were received for subsequent data analysis. Regression results revealed that religiosity and product knowledge significantly influence consumers‟ attitude toward using halal credit card services.  Attitude in turn, subsequently has a significant impact on consumers‟ intention to accept halal financial credit card services. Several theoretical and managerial contributions were observed in this study.   

The boundary layer separation from streamlined surfaces and new ways of its prevention in diffusers

2017 ◽  
Author(s):  
Arkady Zaryankin ◽  
Andrey Rogalev ◽  
Ivan Komarov ◽  
V. Kindra ◽  
S. Osipov
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Separation ◽  
Layer Separation

scholarly journals Perspectives of Healthcare Professionals Regarding Factors Associated with Antimicrobial Resistance (AMR) and Their Consequences: A Cross Sectional Study in Eastern Province of Saudi Arabia

Antibiotics ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 878
Author(s):  
Mohamed A. Baraka ◽  
Amany Alboghdadly ◽  
Samar Alshawwa ◽  
Asim Ahmed Elnour ◽  
Hassan Alsultan ◽  
...  
Keyword(s):  
Antimicrobial Resistance ◽  
Inappropriate Prescribing ◽  
Healthcare Providers ◽  
Cross Sectional Study ◽  
Sectional Study ◽  
Key Factors ◽  
Eastern Province ◽  
Cross Sectional ◽  
Factors Associated ◽  
Factors Influencing

Factors reported in the literature associated with inappropriate prescribing of antimicrobials include physicians with less experience, uncertain diagnosis, and patient caregiver influences on physicians’ decisions. Monitoring antimicrobial resistance is critical for identifying emerging resistance patterns, developing, and assessing the effectiveness of mitigation strategies. Improvement in prescribing antimicrobials would minimize the risk of resistance and, consequently, improve patients’ clinical and health outcomes. The purpose of the study is to delineate factors associated with antimicrobial resistance, describe the factors influencing prescriber’s choice during prescribing of antimicrobial, and examine factors related to consequences of inappropriate prescribing of antimicrobial. A cross-sectional study was conducted among healthcare providers (190) in six tertiary hospitals in the Eastern province of Saudi Arabia. The research panel has developed, validated, and piloted survey specific with closed-ended questions. A value of p < 0.05 was considered to be statistically significant. All data analysis was performed using the Statistical Package for Social Sciences (IBM SPSS version 23.0). 72.7% of the respondents have agreed that poor skills and knowledge are key factors that contribute to the inappropriate prescribing of antimicrobials. All of the respondents acknowledged effectiveness, previous experience with the antimicrobial, and reading scientific materials (such as books, articles, and the internet) as being key factors influencing physicians’ choice during antimicrobial prescribing. The current study has identified comprehensive education and training needs for healthcare providers about antimicrobial resistance. Using antimicrobials unnecessarily, insufficient duration of antimicrobial use, and using broad spectrum antimicrobials were reported to be common practices. Furthermore, poor skills and knowledge were a key factor that contributed to the inappropriate use and overuse of antimicrobials, and the use of antimicrobials without a physician’s prescription (i.e., self-medication) represent key factors which contribute to AMR from participants’ perspectives. Furthermore, internal policy and guidelines are needed to ensure that the antimicrobials are prescribed in accordance with standard protocols and clinical guidelines.

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