Research

For my thesis research, I have been investigating ideas around propulsion and control of aerial vehicles using plasma actuators, with the goal of creating a next generation ultra quiet and efficient aerial vehicle. I also have and interest in environmental science and exploring the real world applications of plasma, particularly in the area of pollution monitoring, sanitization and chemical treatment.

Interests

• Active flow control - separation control, drag reduction and lift augmentation
• Plasma actuators
• Flow measurement techniques
• Low Reynolds number flow
• Aerodynamics
• Electrohydrodynamics
• Dielectric barrier discharge
• Corona discharge
• Electrostatic precipitation

Research Projects

Development of plasma vortex generator and force characterization
Active flow control using plasma actuation
Analytical thrust model development for corona discharge

Electrohydrodynamic (EHD) thrust is produced when ionized fluid is accelerated in an electric field due to the momentum transfer between the charged species and neutral molecules. In this study, we extend the previously reported analytical model that couples space charge, electric field, and momentum transfer to derive thrust force in 1D planar coordinates. The electric current density in the model can be expressed in the form of Mott-Gurney law. After the correction for the drag force, the EHD thrust model yields good agreement with the experimental data from several independent studies. The EHD thrust expression derived from the first principles can be used in the design of propulsion systems and can be readily implemented in the numerical simulations. This project was carried under the guidance of Prof. Igor Novosselov and Prof. Alexander Mamishev

Comparison of state of the art and current model for voltage-current and voltage-thrust characteristics

Electrohydrodynamic thruster for centimeter scale aerial vehicles

To date, insect scale robots capable of controlled flight have used flapping-wings for generating lift, but this requires a complex and failure-prone mechanism. A simpler alternative is electrohydrodynamic (EHD) thrust, which requires no moving mechanical parts. In EHD, corona discharge generates a flow of ions in an electric field between two electrodes; the high-velocity ions transfer their kinetic energy to neutral air molecules through collisions, accelerating the gas and creating thrust. In this study, we utilize laser machining fabrication to build EHD thrusters for centimeter-sized aerial robots. The process allows for use of a greater variety of electrode materials and eliminates the need for a cleanroom facility. For example, it allows fabricating a complete four-thruster device in a matter of minutes. Our four-thruster device measures 1.8 × 2.5 cm and is composed of steel emitters and a lightweight carbon fiber mesh. We measured the electrical current and thrust of each thruster of our four-thruster design, showing agreement with the Townsend relation. The device was able to lift its weight, as indicated by thrust measurements and free-flight connected to a wire tether. The thrust-to-weight ratio of our device at takeoff voltage of 4.6 kV is 1.38 with a power consumption of 0.037 W. The peak thrust-to-weight ratio of our thruster at the maximum actuation voltage of 5.2 kV (with a typical operating range of 3.6 kV to 5.2 kV) is 3.03 with a power consumption of 0.104 W. This project was carried under the guidance of Prof. Igor Novosselov and Prof. Sawyer Fuller

An assembled Quad-thruster robot next to a U.S.penny The 1.8 × 2.5 cm quad-thruster having a mass of 37 mg is shown. The thruster is resting on the table and it was able to lift off at 4.6 kV.

Plasma boundary layer and flow development

An electrohydrodynamic (EHD) flow induced by planar corona discharge in near wall region is investigated in this study experimentally and via a multiphysics computational model. The EHD phenomena has many potential engineering applications but requires a mechanistic understanding of the ion and flow transport. The EHD device consists of two electrodes flush mounted on the surface to create an airflow along the plate. Constant current hotwire anemometry is used to measure the flow velocity profile. The applied voltage between the electrodes is varied and the resulting effects in the charge density and flow field are measured. The airflow near the wall acts a jet and it reaches a maximum of 2 m/s with an energy conversion efficiency of ~3%. The velocity decreases sharply as we move vertically from the plate. Multiphysics numerical model couples ion transport equation and the Navier Stokes equations to solve for the spatiotemporal distribution of electric field, charge density and flow field. The numerical results match experimental data shedding new insights into mass, charge and momentum transport phenomena. The EHD driven flow can be applied to the design of new plasma actuators for flow control. This project was carried under the guidance of Prof. Igor Novosselov and Prof. Alexander Mamishev. This project was supported by the Joint Center for Aerospace Technology Innovation, USA in collaboration with Aerojet Rocketdyne

An assembled Quad-thruster robot next to a U.S.penny The 1.8 × 2.5 cm quad-thruster having a mass of 37 mg is shown. The thruster is resting on the table and it was able to lift off at 4.6 kV.

Miniature PM monitor and in-situ analysis

Exposure to fine and ultrafine particulate matter (PM) from combustion and manufacturing processes can cause significant health effects. The toxic potential of inhaled particles depends on particle size and their chemical composition. Collection of air-borne particles on a filter, their extraction into a solvent like cyclohexane and fluorescence analysis is costly and time consuming. In this study, we demonstrate a novel ultrafine particle electrostatic collector that uses a wire to rod ionizer to charge the particles and ionic wind to drive the flow. The particles are then directed on to a glass slide by the electric field between the collection electrode and repelling electrode. The slide with collected particles was then coated with PDMS (Polydimethylsiloxane). Fluorescence Excitation Emission Matrix (EEM) is used to characterize organic compounds and it can be used to compact, low-cost sensor development This project was carried under the guidance of Prof. Igor Novosselov. This project was supported by the National Institutes of Health, USA

Collected glass slides a) Cigarette smoke and b) Ethane 73% dilution and their respective EEM

Particle behavior in electrohydrodynamic flow

Ultrafine particle behavior in electro-hydrodynamic (EHD) flow induced by corona discharge is studied experimentally and numerically and EHD flow serves as a primary particle sampling mechanism. Multiphysics numerical model couples ion transport equation and the Navier-Stokes equations (NSE) to solve for the spatiotemporal distribution of electric field, charge density, and flow field; the results are compared with experimental velocity profiles at the exit. Experimentally evaluated particle transmission trends for ambient and NaCl nanoparticles in the 20 nm–150 nm range are in good agreement with the theoretical models. However, for particles in the 10 nm–20 nm size range, the transmission is lower due to the increased particle charging resulted from their exposure to the high-intensity electric field and high charge density in the EHD driven flow. These conditions yield a high probability of particles below 20 nm to acquire and hold a unit charge. The transmission is lower for smaller particle (10 nm) due to their high charge to mass ratio, and it increases as the single-charged particles grow in mass up to 20 nm, resulting in their lower electrical mobility. For particles larger than 20 nm, the electrical mobility increases again as they can acquire multiple charges. The results shed insight into interaction of nanoparticle and ions in high electrical field environment, that occur in primary EHD driven flows and in the secondary flows generated by corona discharge. This project was carried under the guidance of Prof. Igor Novosselov. This project was supported by the National Institutes of Health, USA

Schematic of the EHD particle collector Particle collection efficiency as a function of their size

Experimental, numerical and analytical model development for corona discharge

Ultrafine particle behavior in electro-hydrodynamic (EHD) flow induced by corona discharge is studied experimentally and numerically and EHD flow serves as a primary particle sampling mechanism. Multiphysics numerical model couples ion transport equation and the Navier-Stokes equations (NSE) to solve for the spatiotemporal distribution of electric field, charge density, and flow field; the results are compared with experimental velocity profiles at the exit. Experimentally evaluated particle transmission trends for ambient and NaCl nanoparticles in the 20 nm–150 nm range are in good agreement with the theoretical models. However, for particles in the 10 nm–20 nm size range, the transmission is lower due to the increased particle charging resulted from their exposure to the high-intensity electric field and high charge density in the EHD driven flow. These conditions yield a high probability of particles below 20 nm to acquire and hold a unit charge. The transmission is lower for smaller particle (10 nm) due to their high charge to mass ratio, and it increases as the single-charged particles grow in mass up to 20 nm, resulting in their lower electrical mobility. For particles larger than 20 nm, the electrical mobility increases again as they can acquire multiple charges. The results shed insight into interaction of nanoparticle and ions in high electrical field environment, that occur in primary EHD driven flows and in the secondary flows generated by corona discharge. This project was carried under the guidance of Prof. Igor Novosselov. This project was supported by the National Institutes of Health, USA

Schematic of the EHD particle collector Particle collection efficiency as a function of their size

Effect of radiation on electronic cooling

In this study on conjugate convection with surface radiation from a rectangular open cavity equipped with four non-identical flush-mounted discrete heat sources, parametric studies are performed. The governing equations for temperature distribution are evolved through appropriate energy balance between heat generated, conducted, convected and radiated from the cavity. The governing equations are later discretized into algebraic form using finite difference formulation and are subsequently solved simultaneously using Gauss-Seidel iterative solver. A number of parametric studies showcasing the effects of the independent parameters, like aspect ratio, surface emissivity, thermal conductivity and convection heat transfer coefficient, on various important results are made. This project was carried under the guidance of Prof. Gururaja Rao

Detailed study on aerodynamics of flapping aerial vehicles and design of flapping wing mechanism

Other Projects

Airborne virus inactivation using non-thermal plasma reactor
Electromechanical nerve stimulation using TENS device

Education

Publications

• A. Tang¹, R.S. Vaddi¹, A. Mamishev and I. Novosselov, 'Empirical relations for discharge current and momentum injection in dielectric barrier discharge plasma actuators', Journal of Physics D: Applied Physics (2021) 54(24):245204
• U.N. Lee¹, T.L. Neel¹, F.Y. Lim, J.W. Khor, J. He, R.S. Vaddi, A. Q. W. Ong, A. Tang, J. Berthier, J.S. Meschke, I.Novosselov, A.B. Theberge, and E. Berthier, 'Miniaturizing wet scrubbers for aerosolized droplet capture', Analytical Chemistry (2021), 93(33), 11433–11441
• P. Fillingham, R.S. Vaddi, A. Bruning, G. Israel and I. Novosselov, 'Drag, lift, and torque on a prolate spheroid resting on a smooth surface in a linear shear flow', Powder Technology 377 (2021) 958:965
• R.S. Vaddi, Y. Guan, A. Mamishev and I. Novosselov, 'Analytical model for electrohydrodynamic thrust', Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (2020) 476:20200220
• R.S. Vaddi, Y. Guan and I. Novosselov, 'Behavior of ultrafine particles in electro-hydrodynamic flow induced by corona discharge', Journal of Aerosol Science (2020): 105587.
• H.K. Hari Prasad¹, R.S. Vaddi¹, Y.M. Chukewad. E. Dedic, I. Novosselov and S. Fuller 'A laser-microfabricated electrohydrodynamic thruster for centimeter-scale aerial robots', PLoS ONE 15(4):e0231362
• Y. Guan, R.S. Vaddi, A. Aliseda and I. Novosselov, 'Analytical model of electro-hydrodynamic flow in corona discharge', Physics of plasmas 25, no. 8 (2018): 083507.
• Y. Guan, R.S. Vaddi, A. Aliseda and I. Novosselov, 'Experimental and numerical investigation of electrohydrodynamic flow in a point-to-ring corona discharge', Physical Review Fluids 3, no. 4 (2018): 043701.

¹ Authors contributed equally to the work.

Under Review/In Preparation

• R.S. Vaddi, A. Mamishev and I. Novosselov, 'Direct current augmented dielectric barrier discharge plasma actuator: Effect of third electrode', Applied Physics Letters (in preparation)
• R.S. Vaddi, A. Mamishev and I. Novosselov, 'Direct current augmented dielectric barrier discharge plasma actuator: Effect of electrode shape', AIAA Journal (in preparation)
• R.S. Vaddi, C. Sota, A. Mamishev and I. Novosselov, 'Active Flow Control of NACA 0012 airfoil using Sawtooth Direct Current Augmented Dielectric Barrier Discharge Plasma Actuator', Experiments in Fluids (under review)

• Ravi Sankar Vaddi , Gaurav Mahamuni and Igor Novosselov, 'Development of an EHD induced wind driven personal exposure monitor and in-situ analysis for characterization of exposure', XI International Symposium on Electrohydrodynamics, St. Petersburg, Russia, 18-22 June 2019
• Ravi Sankar Vaddi , Yifei Guan, Zhi yan Chen, Alexander Mamishev and Igor Novosselov, 'Experimental and numerical investigation of corona discharge induced flow on a flat plate', XI International Symposium on Electrohydrodynamics, St. Petersburg, Russia, 18-22 June 2019
• Yifei Guan, Ravi Sankar Vaddi , Alberto Aliseda and Igor Novosselov, 'Comparison of Analytical and Numerical Models for Point to Ring Electro- Hydrodynamic Flow', XI International Symposium on Electrohydrodynamics, St. Petersburg, Russia, 18-22 June 2019

• An itty-bitty robot that lifts off like a sci-fi spaceship Wired magazine article

Personal

I was born and raised in Rajahmundry, Andhra Pradesh, India. In my spare time, I love to sketch, paint, I enjoy most of my time being outdoors. In the winter, I am an avid skier and novice ice climber. During the warmer months here in Colorado, I enjoy mountain biking, free climbing, and kayaking.

When forced indoors, I follow a number of sci-fi and fantasy genre movies and television shows, I am an aspiring chef, and I spend a large amount of my free time exploring the latest technology advancements in the front-end web development world.