Experimental Analysis of a Small-Scale Rotor at Various Inflow Angles

Kolaei, Amir; Barcelos, Devin F.; Bramesfeld, Goetz

doi:10.1155/2018/2560370

“…Figure 2-9. TMotor split into 34 elements [6] A test case was used as a base reference for evaluating the effects of splitting DVEs. All parameters were kept the same as the test case except for the fact that splitting was enabled.…”

Section: Test Casementioning

confidence: 99%

Robust Wake Rollup Modelling Using Dyes

Janardhan¹

2021

Preprint

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This project report gives details on a modification of VAPTOR, a program that can predict the aerodynamic performance of aircrafts using a potential flow method with a relaxed wake model. In VAPTOR the wake is modelled using distributed vorticity elements (DVEs). DVEs can induce velocities at certain points used to relax the wake. A DVE has inbuilt singularity protections i.e. prevents the calculated velocity to approach infinity, but when two adjacent DVEs have a very low relative angle, these protections lead to an error in the calculation of the velocity at its shared midpoint during the relaxation process. In most cases these errors are negligible until a rotor is analysed during hover or vortex ring state. In these special cases the wake rollup is more intense leading to relatively small angles. The subsequent errors caused by the singularity protections cannot be ignored since they cause the solutions to be erratic and not smooth. It also causes the wake DVEs to deform disproportionally which is a visual indication of the errors. The modification uses a method that involves splitting the DVE in order to eliminate the errors when calculating the velocity at the junction of two adjacent DVEs. The splitting is temporary and only applied during the calculation of the velocity at the junction. The algorithm for the splitting of the DVE and its implementation into MATLAB is provided in this report. The implementation is tested by ensuring that all conditions are kept the same except when splitting is enabled or disabled. A number of test runs were conducted, and an index called the Smoothness Index was created in order to quantify the improvements of the DVE splitting method. The results shown are promising as the solution with splitting enabled is twice as smooth as when the splitting is disabled. There is also a noticeable improvement during visual comparison of the wake diagrams when splitting is enabled and disabled. The results combined with the fact that the extra computation required to execute the DVE splitting method is negligible, the author recommends it be enabled in all cases. Having said that, the end user has full control whether he or she would like to use it or not. They can also change the parameters of splitting to suit their needs.

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“…The DVE splitting method can be enabled or disabled based on the user's preference. (repmat(cos(acos(dot(ispn_dir,iedge_dir,2))pi/2),1,2)',[],1); % coeff_o=coeff; i= [1,1,1,2,2,3,3,3,3,3,3,4,4,4,4,5,5,5,5,5,5,6,6,6,6,7,7,7,7,7,7,8,8,8 ,8,9,9,9,10,10,11,11,11,11,12,12,12,12]'+(0:12:(n_pair-1)*12);i=i(:); j= [1,2,3,2,3,1,2,3,4,5,6,2,3,5,6,4,5,6,7,8,9,5,6,8,9,7,8,9,10,11,12,8,9,11,12,10,11,12,11,12,1,3,4,6,7,9,10,12]'+(0:12:(n_pair-1)*12);j=j(:); n_idve = reshape(repmat(cross(ispn_dir,iedge_dir),1,2)',3,[])';n_idve=n_idve./s um(n_idve.^2,2).^0.5; a_roll = -atan2(n_adve(:,2),n_adve(:,3)); a_pitch = asin(n_adve(:,1)); aloc_dir = fcnGLOBSTAR((adve (1:4:end-3,:) +adve(2:4:end-2, o=(1:4)+...…”

Section: Chapter 5: Conclusionmentioning

confidence: 99%

Robust Wake Rollup Modelling Using Dyes

Janardhan¹

2021

Preprint

0

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This project report gives details on a modification of VAPTOR, a program that can predict the aerodynamic performance of aircrafts using a potential flow method with a relaxed wake model. In VAPTOR the wake is modelled using distributed vorticity elements (DVEs). DVEs can induce velocities at certain points used to relax the wake. A DVE has inbuilt singularity protections i.e. prevents the calculated velocity to approach infinity, but when two adjacent DVEs have a very low relative angle, these protections lead to an error in the calculation of the velocity at its shared midpoint during the relaxation process. In most cases these errors are negligible until a rotor is analysed during hover or vortex ring state. In these special cases the wake rollup is more intense leading to relatively small angles. The subsequent errors caused by the singularity protections cannot be ignored since they cause the solutions to be erratic and not smooth. It also causes the wake DVEs to deform disproportionally which is a visual indication of the errors. The modification uses a method that involves splitting the DVE in order to eliminate the errors when calculating the velocity at the junction of two adjacent DVEs. The splitting is temporary and only applied during the calculation of the velocity at the junction. The algorithm for the splitting of the DVE and its implementation into MATLAB is provided in this report. The implementation is tested by ensuring that all conditions are kept the same except when splitting is enabled or disabled. A number of test runs were conducted, and an index called the Smoothness Index was created in order to quantify the improvements of the DVE splitting method. The results shown are promising as the solution with splitting enabled is twice as smooth as when the splitting is disabled. There is also a noticeable improvement during visual comparison of the wake diagrams when splitting is enabled and disabled. The results combined with the fact that the extra computation required to execute the DVE splitting method is negligible, the author recommends it be enabled in all cases. Having said that, the end user has full control whether he or she would like to use it or not. They can also change the parameters of splitting to suit their needs.

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“…Figure 8 shows the T-motor geometry that was used in the validation study. Three cases were modelled with a 90-degree angle of attack, which is purely axial freestream flow like it is encountered during climbing flight [27]. The control volume that was used had 3 subregions, as shown in Figure 9, in order to better control grid spacing and element size transition rates.…”

Section: Geometric Modelmentioning

confidence: 99%

Early On-Set Prediction Of Vortex-Ring State Of Quadrotors

McQuaid¹

2021

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The OpenFOAM CFD package was used to initially investigate the aerodynamic effects of vortex-ring state of a quadrotor, then to study various quadrotor flight maneuvers to minimize the thrust loses of vortex-ring state and followed by possible detection methods for a drone entering vortex-ring state. Vortex-ring state is characteristic of a decrease in the effective angle of attack of incoming airflow due to a rotor descending into its downwash. This causes significant loses in the thrust of the rotor, which typically leads to severe flight upsets for rotorcraft. A quadrotor was studied at varying descent velocities to investigate wake roll-up at the rotor tips and the subsequent effects on rotor thrust and power. The quadrotor was then subjected to non-vertical descent angles to investigate thrust loss mitigation approaches due to vortex-ring state. A method of detecting the on-set of vortex-ring state is proposed using various differential pressure measurements on the quadrotor. It has been shown that by monitoring the pressure difference between the top of the quadrotor body and the bottom of one of the quadrotor legs, a pressure drop can be seen just prior to the on-set of vortex-ring state. This pressure drop was shown to occur during descending flight regimes and may prove to be an effective pre-vortex-ring state warning system.

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Experimental Analysis of a Small-Scale Rotor at Various Inflow Angles

Cited by 38 publications

References 21 publications

Robust Wake Rollup Modelling Using Dyes

Robust Wake Rollup Modelling Using Dyes

Robust Wake Rollup Modelling Using Dyes

Early On-Set Prediction Of Vortex-Ring State Of Quadrotors

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