[Paper Review] Dielectric Barrier Discharge Actuators: Experimental and Numerical Study of Momentum Injection into Co-flow and Counter-flow Freestream

Anthony Tang, Nathan Li+4 more|arXiv (Cornell University)|Mar 31, 2023

Plasma and Flow Control in Aerodynamics4 citations

TL;DR

This study experimentally and numerically investigates dielectric barrier discharge (DBD) plasma actuators for momentum injection into co-flow and counter-flow freestreams at Re = 35,000 and 75,000. It reveals that in counter-flow, momentum injection is six times greater than in quiescent conditions, with flow separation and boundary layer thinning observed, highlighting complex coupling between EHD, inertial, viscous, and Coulombic forces beyond simple superposition.

ABSTRACT

Dielectric barrier discharge (DBD) plasma actuators can generate a wall jet without moving parts by interacting with ionized and neutral molecules in an electric field. The coupling between electrohydrodynamic (EHD), turbulence, inertial and viscous effects in the flow boundary layer remains poorly understood and requires investigation. We present an experimental investigation of momentum injection by DBD actuators into the free stream flow with Re = 35,000 and 75,000 in co-flow and counter-flow scenarios over a range of VAC = 12 kV - 19.5 kV peak-to-peak at a frequency of 2 kHz. In the co-flow configuration, the DBD actuator injects momentum into the boundary layer. In co-flow, the momentum injection results in the thinning boundary layer, while in the counter-flow configuration, flow separation can occur. For the tested condition, a separation bubble is observed at Re = 35,000. The momentum displacement in the counter-flow configuration is six times greater than the EHD jet momentum in a quiescent environment. Both co-flow and counter-flow momentum injections show diminishing effects with increasing external velocities. This work highlights that the resulting flow pattern is not a simple superposition of the EHD jet and the free stream but is determined by the coupling of inertial, viscous, and Coulombic effects in the EHD-driven wall jet and the external flow. The velocity profiles and momentum measurements presented here can be used to validate numerical models and inform the design of DBD actuators for active flow control.

Motivation & Objective

• To understand the coupling of electrohydrodynamic (EHD), turbulent, viscous, and inertial effects in DBD-driven wall jets interacting with external flows.
• To quantify momentum injection into co-flow and counter-flow freestreams under varying electric field strengths (12–19.5 kVpp) and Reynolds numbers (35,000–75,000).
• To investigate the formation of separation bubbles and boundary layer modification in counter-flow configurations.
• To validate numerical models using measured velocity profiles and momentum data for active flow control applications.
• To determine whether momentum injection in external flows is a simple superposition of EHD jet and free stream or governed by complex nonlinear interactions.

Proposed method

• Experimental setup with DBD actuators operating at 2 kHz frequency and peak-to-peak voltages from 12 kV to 19.5 kV in wind tunnel configurations.
• Use of particle image velocimetry (PIV) to measure detailed velocity profiles in co-flow and counter-flow arrangements.
• Numerical modeling of EHD-driven wall jets coupled with external freestream flows to simulate momentum transfer and boundary layer dynamics.
• Reynolds number variation via controlled freestream velocity to assess dependence of momentum injection on external flow speed.
• Comparison of momentum displacement in counter-flow to EHD jet momentum in quiescent conditions to quantify enhancement.
• Analysis of boundary layer thickness and separation bubble formation using velocity gradient and streamwise flow reversal criteria.

Experimental results

Research questions

• RQ1 How does momentum injection by DBD actuators vary in co-flow versus counter-flow freestream configurations at Re = 35,000 and 75,000?
• RQ2 To what extent is the momentum transfer in counter-flow enhanced compared to the EHD jet in quiescent conditions?
• RQ3 What role do inertial, viscous, and Coulombic forces play in shaping the resulting flow field when EHD wall jets interact with external flows?
• RQ4 Does the observed flow behavior represent a simple superposition of the EHD jet and freestream, or is it governed by complex nonlinear coupling?
• RQ5 How does increasing external freestream velocity affect the effectiveness of momentum injection in both co-flow and counter-flow modes?

Key findings

• In co-flow configuration, DBD actuators induce boundary layer thinning due to effective momentum injection into the flow.
• In counter-flow, flow separation occurs, with a stable separation bubble observed at Re = 35,000 under tested conditions.
• Momentum displacement in counter-flow is six times greater than the EHD jet momentum in a quiescent environment, indicating significant amplification of momentum transfer.
• Both co-flow and counter-flow momentum injection effects diminish with increasing external freestream velocity, indicating reduced actuator effectiveness at higher flow speeds.
• The resulting flow patterns are not a simple superposition of the EHD jet and external flow, but result from complex coupling of inertial, viscous, and Coulombic forces.
• Measured velocity profiles and momentum data provide critical validation benchmarks for numerical models of EHD-driven flow control systems.