On Transition From Supersonic to Subsonic Flow at Low Reynolds Numbers in a Tube

1969 ◽  
Vol 36 (2) ◽  
pp. 146-150 ◽  
Author(s):  
R. Y. Chen ◽  
J. C. Williams
Keyword(s):  
Mach Number ◽  
Static Pressure ◽  
Subsonic Flow ◽  
Supersonic Nozzle ◽  
Reynolds Numbers ◽  
Impact Pressure ◽  
Low Reynolds Numbers ◽  
Pressure Distributions ◽  
Low Reynolds ◽  
The Impact

A supersonic low-density gas stream produced in a supersonic nozzle was passed through a circular tube in which the transition from supersonic to subsonic flow took place. Static pressure distributions along the tube (and nozzle) and impact pressure distributions across the tube at several stations were measured to determine the nature of this transition. The impact pressure distributions were used, together with the local static pressure, to infer Mach number and velocity profiles in the tube. When the pressure distributions and center-line Mach number distributions are considered together, one obtains a fairly clear picture of the processes involved in the transition from supersonic to subsonic flow at low Reynolds numbers.

Separation and Transition Control on an Aft-Loaded Ultra-High-Lift LP Turbine Blade at Low Reynolds Numbers: High-Speed Validation

2006 ◽  
Vol 129 (2) ◽  
pp. 340-347 ◽  
Author(s):  
Maria Vera ◽  
Xue Feng Zhang ◽  
Howard Hodson ◽  
Neil Harvey
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Surface Finish ◽  
High Speed ◽  
Reynolds Numbers ◽  
High Lift ◽  
Low Reynolds Numbers ◽  
Low Speed ◽  
Transition Mechanism ◽  
Low Reynolds

This paper presents the second part of an investigation of the combined effects of unsteadiness and surface roughness on an aft-loaded ultra-high-lift low-pressure turbine (LPT) profile at low Reynolds numbers. The investigation has been performed using low- and high-speed cascade facilities. The low- and high-speed profiles have been designed to have the same normalized isentropic Mach number distribution. The low-speed results have been presented in the first part (Zhang, Vera, Hodson, and Harvey, 2006, ASME J. Turbomach., 128, pp. 517–527). The current paper examines the effect of different surface finishes on an aft-loaded ultra-high-lift LPT profile at Mach and Reynolds numbers representative of LPT engine conditions. The surface roughness values are presented along with the profile losses under steady and unsteady inflow conditions. The results show that the use of a rough surface finish can be used to reduce the profile loss. In addition, the results show that the same quantitative values of losses are obtained at high- and low-speed flow conditions. The latter proves the validity of the low-speed approach for ultra-high-lift profiles for the case of an exit Mach number of the order of 0.64. Hot-wire measurements were carried out to explain the effect of the surface finish on the wake-induced transition mechanism.

Vortex-induced rotations of a rigid square cylinder at low Reynolds numbers

2017 ◽  
Vol 813 ◽  
pp. 482-507 ◽  
Author(s):  
Sungmin Ryu ◽  
Gianluca Iaccarino
Keyword(s):  
Cross Flow ◽  
Reynolds Numbers ◽  
Dynamic Responses ◽  
Two Dimensional ◽  
Square Cylinder ◽  
Low Reynolds Numbers ◽  
Pressure Distributions ◽  
Low Reynolds ◽  
Drag And Lift ◽  
Vortex Patterns

A numerical investigation of vortex-induced rotations (VIRs) of a rigid square cylinder, which is free to rotate in the azimuthal direction in a two-dimensional uniform cross-flow, is presented. Two-dimensional simulations are performed in a range of Reynolds numbers between 45 and 150 with a fixed mass and moment of inertia of the cylinder. The parametric investigation reveals six different dynamic responses of the square cylinder (expanding on those reported by Zaki et al. (J. Fluids Struct., vol. 8, 1994, pp. 555–582)) and their coupled vortex patterns at low Reynolds numbers. In each characteristic regime, moment generating mechanisms are elucidated with investigations of instantaneous flow fields and surface pressure distributions at chosen time instants in a period of rotation response. Our simulation results also elucidate that VIRs significantly influence the statistics of drag and lift force coefficients: (i) the onset of a rapid increases of the two coefficients at $Re=80$ and (ii) their step increases in the autorotation regime.

Influence of a Finite Width Micro-Tab on the Spanwise Lift Distribution

2013 ◽  
Author(s):  
D. Holst ◽  
A. B. Bach ◽  
C. N. Nayeri ◽  
C. O. Paschereit
Keyword(s):  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Global Changes ◽  
Finite Width ◽  
Local Pressure ◽  
Low Reynolds Numbers ◽  
Pressure Distributions ◽  
Coefficient Distribution ◽  
Stereo Particle Image Velocimetry ◽  
The Impact

The results of surface pressure measurements are presented in this paper to gain further insight into the lift changing influence of finite width micro-tabs, especially in adjacent airfoil sections. Micro-tabs are a promising concept for load control on wind turbines. Local pressure distributions were measured in several rows of pressure taps in the vicinity of the finite width micro-tab attached to a FX 63-137 profile at low Reynolds numbers. The investigation focuses on length dependency, chordwise position, and interaction between two micro-tabs. Additionally, stereo Particle-Image-Velocimetry measurements were conducted to study the structure, sense of rotation, and influence of tab-induced tip vortices, as well as the impact of a finite width micro-tab on the model’s near wake. Experiments reveal relative changes of more than 30 % in the pressure coefficient distribution upstream of several micro-tab configurations. Furthermore, increments of 20 % are recorded in neighbouring sections not directly controlled by micro-tabs. Even higher changes are obtained in the region between two tabs. These improvements are attained due to local and global changes in the effective camber.

Separation and Transition Control on an Aft-Loaded Ultra-High-Lift LP Turbine Blade at Low Reynolds Numbers: High-Speed Validation

2005 ◽  
Author(s):  
Maria Vera ◽  
Xue Feng Zhang ◽  
Howard Hodson ◽  
Neil Harvey
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Surface Finish ◽  
High Speed ◽  
Reynolds Numbers ◽  
High Lift ◽  
Low Reynolds Numbers ◽  
Low Speed ◽  
Transition Mechanism ◽  
Low Reynolds

This paper presents the second part of an investigation of the combined effects of unsteadiness and surface roughness on an aft-loaded ultra high lift low pressure turbine (LPT) profile at low Reynolds numbers. The investigation has been performed using low-speed and high-speed cascade facilities. The low speed and the high speed profiles have been designed to have the same normalized isentropic Mach number distribution. The low speed results have been presented in Part 1 of this paper. The current paper examines the effect of different surface finishes on an aft-loaded ultra-high-lift LPT profile at Mach and Reynolds numbers representative of LPT engine conditions. The surface roughness values are presented along with the profile losses under steady and unsteady inflow conditions. The results show that the use of a rough surface finish might reduce the profile loss. In addition, the results show that the same quantitative values of losses are obtained at high and low speed flow conditions. The latter proves the validity of the low speed approach for ultra high lift profiles for the case of an exit Mach number of the order of 0.64. Hot wire measurements were carried out to explain the effect of the surface finish on the wake induced transition mechanism.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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