Drone Scale Coaxial Rotor Aerodynamic Interactions Investigation

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Dhwanil Shukla ◽  
Narayan Komerath
Keyword(s):  
High Speed ◽  
Vortex Sheet ◽  
Reynolds Numbers ◽  
Thrust Coefficient ◽  
Low Reynolds Numbers ◽  
Rotor Aerodynamics ◽  
Induced Drag ◽  
Coaxial Rotor ◽  
Simplifying Assumptions ◽  
Uninhabited Aerial Vehicles

Coaxial rotor uninhabited aerial vehicles (UAVs) are compact compared to single rotor UAVs of comparable capacity. At the low Reynolds numbers (Re) where they operate, the simplifying assumptions from high Re rotor aerodynamics are not valid. The low Re coaxial rotor flowfield is studied including aerodynamic interactions and their effect on performance. The evolution of the wake is captured using high-speed stereo particle image velocimetry (SPIV). Improvement of upper rotor performance due to viscous swirl recovery from the lower rotor is discovered and then verified by analyzing PIV data. Interesting vortex–vortex sheet interactions are observed under the coaxial rotor affecting wake structure spatially and temporally. A qualitative model explaining the observed wake interaction phenomena is presented. Comparison with the performance of high Re rotors shows higher profile and induced drag at low Re for the same thrust coefficient.

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.

scholarly journals Studying the unsteady characteristics of a laminar transonic buffet depending on the angle of attack

2021 ◽  
Vol 2057 (1) ◽  
pp. 012009
Author(s):  
P A Polivanov ◽  
A A Sidorenko
Keyword(s):  
Shock Wave ◽  
Unsteady Flow ◽  
High Speed ◽  
Angle Of Attack ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Unsteady Characteristics ◽  
Basic Experiments ◽  
Transonic Buffet ◽  
Amplitude Characteristics

Abstract Laminar transonic buffet on the airfoil for low Reynolds numbers of 0.5-0.7⋅106 was experimentally studied. Basic experiments were performed using high-speed schlieren imaging. The unsteady flow structure was investigated using various methods. It was found that shock wave oscillations can be significantly different from the turbulent case. The frequency and amplitude characteristics of oscillations from the angle of attack were found.

Micro Vortex Flow Induced by Small Life

2007 ◽  
Author(s):  
O. Mochizuki
Keyword(s):  
High Speed ◽  
Ccd Camera ◽  
Reynolds Numbers ◽  
Artemia Salina ◽  
The Body ◽  
Power Stroke ◽  
Low Reynolds Numbers ◽  
Flapping Motion ◽  
Vortex Pairs ◽  
Low Reynolds

We investigated the relations between swimming motions and flow fields around plankton that is a larva of brine-shrimp (Artemia salina) and jellyfish (Aurelia aurita). These move in low Reynolds numbers by flapping motion in common. We recorded motions and flow by using a high speed CCD camera, and analyzed by a motion analysis and PIV method. We observed vortex pairs in each case as a result of power stroke and recovery stroke of pitching motion. Force acting on the body was estimated by measured acceleration of the body. Mechanism of generation of thrust force related to vortex pairs by flapping motion in low Reynolds number environment was discussed in this paper.

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.

Effect of Roughness and Unsteadiness on the Performance of a New LPT Blade at Low Reynolds Numbers

2008 ◽  
Author(s):  
Francesco Montomoli ◽  
Howard Hodson ◽  
Frank Haselbach
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Beneficial Effect ◽  
High Speed ◽  
Reynolds Numbers ◽  
High Lift ◽  
Low Reynolds Numbers ◽  
University Of Cambridge ◽  
Wake Passing ◽  
Lower Loss

This paper presents a study of the performance of a high lift profile for low pressure turbines at Reynolds numbers lower than in previous investigations. The separate and combined effects of roughness and wake passing are compared. The effect of incidence on cascade losses is also evaluated. The experimental investigation was carried out in the high speed wind tunnel of Whittle Laboratory, University of Cambridge. This is a closed circuit, continuous wind tunnel where the Reynolds number and Mach number can be fixed independently. The unsteadiness caused by wake passing in front of the blades is reproduced using a wake generator with rotating bars. The results obtained confirm that the beneficial effect of unsteadiness on losses is also present at the lowest Reynolds number examined (Re3 = 0.2×105). Roughening the surface also had a beneficial effect on the losses but this effect vanishes at the lower Reynolds numbers, i.e. (Re3 ≤ 0.3×105), where the surface becomes hydraulically smooth. The present study suggests that a blade with as-cast surface roughness has a lower loss than a polished one.

scholarly journals Turbulent Superstructures in Inert Jets and Diffusion Jet Flames

Fluids ◽  
2021 ◽  
Vol 6 (12) ◽  
pp. 459
Author(s):  
Vadim Lemanov ◽  
Vladimir Lukashov ◽  
Konstantin Sharov
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Near Field ◽  
Reynolds Numbers ◽  
Transverse Dimension ◽  
Diffusion Combustion ◽  
Measuring Instruments ◽  
Low Reynolds Numbers ◽  
Time Flow ◽  
Scale Motion

An experimental study of spatially localized very large-scale motion superstructures, propagating in a jet of carbon dioxide at low Reynolds numbers, was carried out. A hot-wire anemometer and a high-speed 2D PIV with a frequency of 7 kHz were used as measuring instruments. Such a puff-type superstructure in a jet with a longitudinal dimension of up to 20–30 nozzle diameters are initially formed in the jet source—a long tube in a laminar-turbulent transition mode (without artificial disturbances). It is shown that this regime with intermittency in time, when part of the time flow is laminar and the other part of time is turbulent, exists both at the exit from the nozzle and in the near field of the jet. Thus, the structural stability of such turbulent superstructures in the near field of the jet was found. Despite the large longitudinal scale, these formations have a transverse dimension of the order of several nozzle diameters. These structures have a complex internal topology, that is, superstructures are a conglomeration of vortices of different sizes from macroscale to microscale. Using the example of diffusion combustion of methane in air, it is demonstrated that in reacting jets, the existence of such large localized perturbations is a powerful physical mechanism for a global change in the flame topology. At the same time, the presence of a cascade of vortices of different sizes in the puff composition can lead to fractal deformation of the flame front.

Drop Formation in Non-Newtonian Jets at Low Reynolds Numbers

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
V. Dravid ◽  
P. B. Loke ◽  
C. M. Corvalan ◽  
P. E. Sojka
Keyword(s):  
High Speed ◽  
Reynolds Numbers ◽  
Shear Thinning ◽  
Liquid Jets ◽  
Initial Increase ◽  
Low Reynolds Numbers ◽  
Subsequent Decrease ◽  
Satellite Drops ◽  
Element Approach ◽  
Secondary Objective

The objective of this study was to develop an experimentally verified computational model that accurately predicts evolution of shear-thinning liquid jets. A secondary objective was to investigate the formation of satellite drops and to determine conditions under which their diameter can be controlled. The model employs the Galerkin finite/element approach to solve the complete two-dimensional set of axisymmetric governing equations and the corresponding kinematic and dynamic boundary conditions at the free surface. The effect of shear-thinning behavior on breakup was studied in detail for the case of an infinitely long non-Newtonian jet. It was found that shear-thinning behavior may be useful in controlling satellite drop sizes. (We observe that increasing the shear-thinning behavior at Re∼5 leads to an initial increase in the satellite drop size, followed by a subsequent decrease.) Comparison of model predictions with experimental data is presented for the case of a shear-thinning non-Newtonian jet. The experimental liquid was pumped through a capillary and drop shapes obtained using a high speed camera. The experimentally obtained shapes were compared to those predicted by the model and found to be in good agreement.

The Development of a Closed Loop High Speed Cascade Wind Tunnel for Aerodynamic and Heat Transfer Testing at Moderate to Low Reynolds Numbers

2013 ◽  
Author(s):  
M. P. Mihelish ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
High Speed ◽  
Closed Loop ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Low Reynolds Number Flows ◽  
Low Reynolds ◽  
Reynolds Number Flows ◽  
Very High

Engine companies typically emphasize research which has been conducted at conditions as close to engine conditions as possible. This focus on engine relevant conditions often causes difficulties in University research laboratories. One particularly difficult testing regime is high speed but low Reynolds number flows. High speed low Reynolds number flows can occur in both low pressure turbines under a normal range of engine operating conditions and in high pressure turbines run at very high altitudes. This paper documents a new steady state closed loop wind tunnel facility which has been developed to study high speed cascade flows at low Reynolds numbers. The initial test configuration has been representative of a first stage vane configuration for a UAV turbofan which flies at a very high altitude. The initial test section was configured in a three full passage four-vane linear cascade arrangement with upper and lower bleed flows. Both heat transfer and aerodynamics loss measurements were acquired and are presented in this paper. Heat transfer measurements were taken at a Reynolds number of 720,000 based on true chord and exit conditions at Mach numbers of 0.7, 0.8, and 0.9. Exit survey measurements were conducted at a chord exit Reynolds number of 720,000 over a similar range in Mach numbers. However, this facility has the capability to run at chord Reynolds numbers of 90,000 or below in the present configuration which uses an approximately three times scale test vane.

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