Scaling relations for the geometry of wire-to-airfoil atmospheric ionic thrusters

Blade emitters for atmospheric ionic thrusters

“…The gap length therefore heavily influences the optimal operating range of the thruster, thus posing a strong constraint on the sizing of the electrical structures used. This behavior is to be expected since increasing the gap at constant spacing will favor parasitic interactions between emitters and increase the inception voltage [13,16]. While the increase of the ignition voltage with the gap is a well known property in literature [24,25], in the present tests a remarkable result is that also the actual corona inception voltage exhibits the same behavior.…”

“…The airfoils ends are protected by insulating caps. In this setup the collectors are airfoils of the National Advisory Committee for Aeronautics (NACA) family, extensively characterized and already used in thrusters which achieved a good performance [6,12,13]. In this study, the shape is fixed and corresponds to a NACA0024 airfoil with a chord of 25 mm, as this was shown to maximize the thrust and thrust-to-power coefficients under conditions similar to the present ones and in a wide range of geometrical and electrical parameters [13].…”

“…Moreover, decreasing the gap would decrease the thrust-to-power ratio and increase the mass of the final thruster, which depends on the power demand. In this regard, in the literature the range of interest of S/d for some wire-cylinder geometries lies approximately between 0.1-3.5 [19,22], while for wire-airfoil geometries is between 0.4 and 5 [13,17,20]. Optimal values which maximize thrust density can be found, however they may depend on the configuration under study: for airfoil collectors in particular, besides S/d, their chord-to-gap and thickness-to-gap ratios c/d, t/d also affect the performance, so that for different airfoils of the NACA family the optimal S/d ratios appear in a range between 0.5 and 1.5 [20,23].…”

“…First and foremost, the phenomenon of multiple emitters unscalability represents the main scientific limit for such thrusters. In fact, in several systems [13][14][15][16][17] it has been observed that increasing the number of the emitters does not lead to a proportional increase in the ionic wind, because an array of emitters at the same potential may create a local region of low potential gradient with detrimental effect on the emitter-collector field, and this effect can be worsened by the hydrodynamic interactions between parallel ionic wind jets. This shielding effect, mathematically described as a deviation from Peek's inception law [18], increases the inception voltage of the emitters.…”

“…When dealing with studies on the electrodes' geometry, it is important to introduce proper scaling relations in order to identify the physically meaningful parameters and avoid introducing repeated tests which involve similar physics on different scales. This problem has been addressed in different works [12,13,19,20], and it has been shown by [13] that the shielding effect for a given emitter shape is highly dependent on the spacing-to-gap ratio S/d. By increasing the spacing S between emitters or reducing the emitters-collectors gap d their ratio increases and the detrimental electrostatic interaction can be reduced, thereby promoting a better emitter-collector interaction.…”