Influence of propeller slipstream on vortex flow field over a typical micro air vehicle

2016 ◽  
Vol 121 (1235) ◽  
pp. 95-113 ◽  
Author(s):  
S. Sudhakar ◽  
A. Chandankumar ◽  
L. Venkatakrishnan
Keyword(s):  
Flow Field ◽  
Vortex Flow ◽  
Surface Flow ◽  
Micro Air Vehicle ◽  
Stereoscopic Particle Image Velocimetry ◽  
Flow Visualisation ◽  
Flow Topology ◽  
Freestream Velocity ◽  
Air Vehicle ◽  
Oil Flow

ABSTRACTAn experimental study has been carried out to explore the effect of propeller-induced slipstream on the vortex flow field on a fixed-wing Micro Air Vehicle (MAV). Experiments were conducted at a freestream velocity of 10 m/s, corresponding to a Reynolds number based on a root chord of about 1.6 × 105. Surface flow topology on the surface of the MAV wing at propeller-off and propeller-on conditions was captured using surface oil flow visualisation at four angles of incidence. The mean off-body flow over the MAV was documented in the four spanwise planes at different chord position using Stereoscopic Particle Image Velocimetry (SPIV) technique at angle-of-attack of 24° for both conditions. The oil flow visualisation showed minimal differences in flow patterns for propeller-off and propeller-on conditions at 10° and 15° incidence. The small asymmetry between port and starboard side observed at 20° during the propeller-off condition became significantly pronounced at 24°. The fuselage stub which is necessary for housing the motor of the propeller was seen to have a significant effect on the flow symmetry at large incidences that can occur when the MAV encounters sudden vertical gusts. Switching on the propeller restored the symmetry at both incidences. SPIV measurements were carried out at the incidence of 24° which exhibited the highest asymmetry. The off-body data shows the re-establishment of symmetry during propeller-on condition owing to the increase in the magnitude of spanwise and vertical velocities as a result of the propeller slipstream. The findings emphasise the importance of considering the propeller flow and design of the motor housing while evaluating the aerodynamics of low-aspect-ratio MAVs.

scholarly journals On the scaling and topology of confined bluff-body flows

2019 ◽  
Vol 876 ◽  
pp. 1018-1040 ◽  
Author(s):  
C. L. Ford ◽  
P. M. Winroth
Keyword(s):  
Bluff Body ◽  
Surface Flow ◽  
Mode Interaction ◽  
Flow Visualisation ◽  
Mode Ii ◽  
Dimensionless Frequency ◽  
Bluff Bodies ◽  
Flow Topology ◽  
Close Coupling ◽  
Vortex Pattern

An experimental study of bluff bodies in confinement is presented. Two Reynolds matched rigs (pipe diameters: $D=40~\text{mm}$ and $D=194~\text{mm}$) are used to derive a picture of the flow topology of the primary-shedding mode (Kármán vortex, mode-I). Confined bluff bodies create an additional spectral mode (mode-II). This is caused by the close coupling of the shedder blockage and the wall and is unique to the confined bluff-body problem. Under certain conditions, modes-I and II can interact, resulting in a lock-on, wherein the modes cease to exist at independent frequencies. The topological effects of mode interaction are demonstrated using flow visualisation. Furthermore, the scaling of mode-II is explored. The two experimental facilities span Reynolds numbers (based on the shedder diameter, $d$) $10^{4}<Re_{d}<10^{5}$ and bulk Mach numbers $0.02<M_{b}<0.4$. Bluff bodies with a constant blockage ratio ($d/D$), forebody shape and various splitter-plate lengths ($l$) and thicknesses ($t$) are used. Results indicate that the flow topology changes substantially between short ($l<d$) and long ($l>d$) tailed geometries. Surface flow visualisation indicates that the primary vortex becomes anchored on the tail when $l\gtrsim 3h$ ($2h=d-t$). This criterion prohibits the development of such a topology for short-tailed geometries. When mode interaction occurs, which it does exclusively in long-tailed cases, the tail-anchored vortex pattern is disrupted. The onset of mode-II occurs at approximately the same Reynolds number in both rigs, although the associated dimensionless frequency is principally a function of Mach number. Accordingly, mode interaction is avoided in the larger-scale rig, due to the increased separation of the modal frequencies.

Analytical and Finite Element Modal Analysis of a Hyperelastic Membrane for Micro Air Vehicle Wings

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Uttam Kumar Chakravarty
Keyword(s):  
Finite Element ◽  
Natural Frequencies ◽  
Wind Tunnel Test ◽  
Element Model ◽  
Micro Air Vehicle ◽  
Finite Element Models ◽  
Freestream Velocity ◽  
Modal Characteristics ◽  
Aerodynamic Pressure ◽  
Air Vehicle

Analytical and finite element models are developed for investigating the modal characteristics of a hyperelastic rubber latex membrane for micro air vehicle wings applications. A radially prestretched membrane specimen is attached to a thin, rigid circular ring and vibrated in vacuum and in air at atmospheric pressure. The natural frequencies of the membrane computed by analytical and finite element models are correlated well. The natural frequencies increase with mode and prestretch level of the membrane but decrease in air from those in vacuum due to the effect of added mass of air. The damping is low and has a very minimal effect on the frequencies but helps to reduce the amplitude of vibration. Aerodynamic pressure at different angles of attack and a freestream velocity is computed from the wind tunnel test data, and a finite element model is developed for investigating the effect of the aerodynamic pressure on the modal characteristics of the membrane. It is found that the effect of aerodynamic pressure on the natural frequencies of the membrane is not significant.

Alleviation of pitch-up on delta wings using distributed porosity

1999 ◽  
Vol 103 (1025) ◽  
pp. 339-347 ◽  
Author(s):  
L. W. Traub ◽  
B. Moeller ◽  
S. F. Galls
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Delta Wing ◽  
Leading Edge ◽  
Surface Flow ◽  
Force Balance ◽  
Flow Visualisation ◽  
Surface Porosity ◽  
Delta Wings ◽  
Field Surveys

Abstract An experimental investigation was undertaken to determine the effectiveness of distributed surface porosity for the alleviation of pitch-up on a delta wing. Tests were undertaken using a 65° sweep delta wing with distributed porosity evaluated at various locations on the wing. Force balance, on and off surface flow visualisation and flow field surveys using a multi-hole probe were undertaken. The data shows that distributed porosity applied along the wing leading edge at the apex is effective in eliminating pitch-up whilst incurring a minimal performance cost. Trailing edge porosity generally degraded performance.

scholarly journals Visualization of flow field around a Micro Air Vehicle with mechanical flapper

2007 ◽  
Vol 27 (Supplement1) ◽  
pp. 83-84
Author(s):  
Hiroyuki OGUSU ◽  
Mizuki NAKAMURA ◽  
Masayoshi FUKAWA ◽  
Akiyoshi IIDA
Keyword(s):  
Flow Field ◽  
Micro Air Vehicle ◽  
Air Vehicle

An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

2021 ◽  
pp. 1-20
Author(s):  
Liesbeth Konrath ◽  
Dieter Peitsch ◽  
Alexander Heinrich
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Complex Flow ◽  
Flow Topology ◽  
Linear Compressor ◽  
Near Surface ◽  
Oil Flow ◽  
Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0deg to 5deg for both blades indicates at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down.

Computational and experimental study of intake ground vortices

2010 ◽  
Vol 114 (1162) ◽  
pp. 769-784 ◽  
Author(s):  
S. Zantopp ◽  
D. MacManus ◽  
J. Murphy
Keyword(s):  
Flow Field ◽  
Local Maximum ◽  
Internal Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Scale Model ◽  
Navier Stokes ◽  
Complex Flow ◽  
Freestream Velocity ◽  
Crossflow Velocity ◽  
Experimental Approaches

Abstract The ground vortices generated by an intake under both headwind and crosswind configurations have been investigated using computational and experimental approaches. The flow field of a scale-model intake was experimentally studied using stereoscopic particle image velocimetry to measure the ground vortex in conjunction with induct total pressure measurements for the internal flow. The computational predictions were performed using an unsteady Reynolds averaged Navier-Stokes approach. The experimental results show that under crosswind conditions a single ground vortex forms which becomes stronger as the crossflow velocity is increased. Under headwind conditions the measured ground vortex strength initially increases with freestream velocity before it reaches a local maximum and then reduces thereafter. The computations also exhibit the same characteristics and show good agreement with the measurements for some configurations. Based on the predictions, the complex flow field topology is investigated and a detailed flow model of the vortex flow field under crosswind conditions is proposed.

An Analysis of the Secondary Flow Around a Tandem Blade Under the Presence of a Tip Gap in a High-Speed Linear Compressor Cascade

2020 ◽  
Author(s):  
Liesbeth Konrath ◽  
Dieter Peitsch ◽  
Alexander Heinrich
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Complex Flow ◽  
Flow Topology ◽  
Linear Compressor ◽  
Near Surface ◽  
Oil Flow ◽  
Linear Compressor Cascade

Abstract Tandem blades have often been under investigation, experimentally as well as numerically, but most studies have been about tandem blade stators without tip gap. This work analyzes the influence of a tip gap on the flow field of a tandem blade for engine core compressors. Experiments have been conducted in a high-speed linear compressor cascade on a tandem and a reference geometry. The flow is analyzed using five-hole probe measurements in the wake of the blades and oil flow visualization to show the near surface stream lines. First, the results for design conditions (tandem and conventional blade) are compared to measurements on corresponding blades without tip gap. Similarities and differences in the flow topology due to the tip clearance are analyzed, showing that the introduction of the tip clearance has a similar influence on the loss and turning development for the tandem and the conventional blade. The tandem blade features two tip clearance vortices with a complex flow interaction and the possible formation of a third counter-rotating vortex between them. An incidence variation from 0° to 5° for both blades indicate at first a similar behavior. After a separation of the flow field into gap and non-gap half it becomes apparent that the tandem blade shows higher losses on the gap side, while featuring a close-to-constant behavior on the non-gap side. Further investigation of the flow on the gap side shows indicators of the front blade exhibiting tip clearance vortex break down, while the rear blade seems unaffected.

scholarly journals Wake Structures and Surface Patterns of the DrivAer Notchback Car Model under Side Wind Conditions

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 320 ◽  
Author(s):  
Dirk Wieser ◽  
Christian Navid Nayeri ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Field ◽  
Aerodynamic Force ◽  
Middle Part ◽  
Surface Flow ◽  
Stereoscopic Particle Image Velocimetry ◽  
Ring Vortex ◽  
Particle Image Velocimetry System ◽  
Rear Window ◽  
Base Surface ◽  
Surface Patterns

The flow field topology of passenger cars considerably changes under side wind conditions. This changes the surface pressure, aerodynamic force, and drag and performance of a vehicle. In this study, the flow field of a generic passenger vehicle is investigated based on three different side wind angles. The study aimed to identify vortical structures causing changes in the rear pressure distribution. The notchback section of the DrivAer model is evaluated on a scale of 1:4. The wind tunnel tests are conducted in a closed section with a splitter plate at a Reynolds number of 3 million. The side wind angles are 0 ∘ , 5 ∘ , and 10 ∘ . The three-dimensional and time-averaged flow field downstream direction of the model is captured by a stereoscopic particle image velocimetry system performed at several measurement planes. These flow field data are complemented by surface flow visualizations performed on the entire model. The combined approaches provide a comprehensive insight into the flow field at the frontal and side wind inflows. The flow without side wind is almost symmetrical. Longitudinal vortices are evident along the downstream direction of the A-pillar, the C-pillars, the middle part of the rear window, and the base surface. In addition, there is a ring vortex downstream of the vehicle base. The side wind completely changes the flow field. The asymmetric topology is dominated by the windward C-pillar vortex, the leeward A-pillar vortex, and other base vortices. Based on the location of the vortices and the pressure distributions measured in earlier studies, it can be concluded that the vortices identified in the wake are responsible for the local minima of pressure, increasing the vehicle drag.

Flow field studies on a micro-air-vehicle-scale cycloidal rotor in forward flight

2014 ◽  
Vol 55 (12) ◽  
Author(s):  
Andrew H. Lind ◽  
Tejaswi Jarugumilli ◽  
Moble Benedict ◽  
Vinod K. Lakshminarayan ◽  
Anya R. Jones ◽  
...  
Keyword(s):  
Flow Field ◽  
Field Studies ◽  
Micro Air Vehicle ◽  
Forward Flight ◽  
Air Vehicle
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