H.O.M.E.R.: The Idea Originating the ACHEON Project
H.O.M.E.R. nozzle concept produces a fully controllable flux, with the ability to maintain a predefined direction and to change this direction arbitrarily as a function of momentum (or velocity) of two primitive streams and of the geometric configuration of the nozzle itself.
Figure 1 – Representation of the nozzle and its behaviour
Figure 1 shows the architecture of the nozzle. It can have any arbitrary geometry as long as it is constituted by a duct (1) eventually bipartite into two channels by a central septum. The two channels converge into the nozzle outlet, connected to two Coanda surfaces (3) and (3’).
This nozzle is different, more rational and simple than any other jet vector system ever conceived before. It has the ability to permit the stabilization of a synthetic jet with an arbitrary predefined direction and to modify this direction dynamically without any moving mechanical part. It generates a vector and controllable jet by the combined action of two different physical phenomena: the mixing of two primitive jets (2) and (2′) and the angular deviation of the resulting synthetic jet by adhering to the Coanda surfaces (3) and (3’).
The synthetic jet is generated and governed by two primitive jets (2) and (2’) by varying their momentums. Physical quantities which guarantee the controllability of the deflection angle of the synthetic jets are the momentum – or speed, for homogeneous jets – and geometric dimensions and design of the nozzle. Minimal operating conditions are related to the Reynolds number (Re > 5000) of the synthetic jet (4) in correspondence to the nozzle outlet. In case of lower Reynolds numbers the system behaviour is unpredictable.
It has been verified that this nozzle can produce an angular deviation of a synthetic jet with no moving mechanical parts, and change the direction of the synthetic jet dynamically. It has been also verified that the synthetic jet always deflects on the side of the primitive stream with the maximum momentum. Referring to Figure 1 the following conditions can be identified:
- if the momentum of the primitive jet (2) is greater than the one of (2’) the synthetic jet (4) adheres to the Coanda surface designated as (3);
- if the momentum of the primitive jet (2’) is greater than the one of (2) the synthetic jet (4) adheres to the Coanda surface designated as (3’);
- if momentums are equal the synthetic jet is straight aligned with the nozzle axis.
The angle formed by the synthetic jet (4) and the geometrical axis of the nozzle can be controlled by the momentums of the primitive jets (2) and (2’). It can be increased when the difference between the moments of the two primitive jets (2) and (2′) increases, can be decreased when it decreases and becomes null when it is zero.
PEACE the second idea originating the project
The second IDEA originating the ACHEON project is in the PEACE system which is in a very preliminary stage of development. It is the PEACE project started at Universidade da Beira Interior. PEACE is the acronym of Plasma Enhanced Actuator for Coanda Effect. PEACE aims to produce an active control of the Coanda adhesion to a surface by means of the BSD technology (Dielectric Barrier Discharge) which can enhance and control adhesion of the synthetic by an active control system.
A plasma actuator consists of two offset thin electrodes that are separated by a layer of dielectric insulator material (Figure 2). One electrode is exposed to the air. The other is fully covered by a dielectric material.
The electrode exposed to air is assumed to be loaded by a high voltage, whereas an electrode buried under the dielectric is expected to be grounded. A high voltage AC potential (high-amplitude (several kV) and high-frequency (typically several kHz) AC voltage) is supplied to the electrodes. This effect permits a partial ionization in the region of the largest electric potential, which usually begins at the edge of the electrode that is exposed to the air, and spreads out over the area projected by the covered electrode.
The ionized air (plasma) in the presence of the electric field produces an attraction/repulsion on the surrounding air. Ionized particles are accelerated and transmit their momentum, through collision, to the neutral air particles in the plasma region over the covered electrode. The result is an acceleration of the air in proximity of the surface of the dielectric.
Figure 2 – Schematic of Plasma actuator method
This technology permits an active control on the Coanda effect by means of a very simple system with very high advantages against Coanda adhesion control by control jets.
DBD plasma actuators have a large number of advantages over other active flow control devices:
- very simple, fully electronic, no moving parts
- operated in either steady (continuous) and unsteady (pulsed or duty cycle) modes;
- low power consumption (0,0067-0,0134 Watts per mm for unsteady operation);
- simple integration, maintenance and operating costs;
- it does not affect surfaces and their aerodynamic performances,
- conformability to any surface curvature;
- high mechanical resistance, affordability and durability;,
- fast response for feedback control due to high bandwidth and possibility of closed-loop feedback control;
- possible modulation in terms of frequency and of power variations.
Potential Applications to Aerial Transport Systems
Jet deflection systems are an important enabling technology for novel of air vehicle concepts with enhanced performance, manoeuvrability, shorter takeoff and landing spaces: It permits the exploration of radical new aerial vehicle concepts, and gives a realization to some very advanced concepts which have been proposed during the history of aviation but could not be applied because of the absence of an effective and affordable jet vector system.
The main importance of an effective and affordable system to control the direction of a propulsive jet can be interesting because it could enable many directions of aeronautic design development:
improving performance, safety, efficiency and manoeuvrability of today’s air vehicle concepts;
defining future air vehicle designs, which include innovative concepts such as control without vertical empennages and reduction of mobile ailerons, and innovative aerodynamic concepts which require directional control of propulsive jets;
analysis of the most efficient and environmental friendly aircraft models based on distributed propulsion systems and on novel propulsive concepts;
investigation of novel aerial vehicle concepts which are optimized to enhance and maximize the possibilities which are guaranteed by similar technologies;
exploration of novel aerial vehicle guidance models and, in particular, novel trajectories, novel manoeuvring enabling technologies such as vector flight and most efficient aerodynamic configurations;
delivery of novel propulsive which can reduce the emission greenhouse gasses such as electrical turbofan, which can be powered by renewable or photovoltaic electricity.
It has been demonstrated by the experiences gained in the last 4/5 decades, that control based on sophisticated mechanical systems can only be suitable for military combat planes and for very short operational periods (combat flight), because they lack in terms of affordability and safety.
The key element to define a decisive breakthrough by using this propulsion system is related to the definition of novel aerial vehicle architectures which can take the maximum advantage from the H.O.M.E.R. nozzle concept. In particular different architectures with different operational models can be tested and verified both by CFD simulation (to identify best operative solutions) and by testing reduced scale radio-controlled (RC) models of the most promising architectures so to acquire the necessary operative experiences which can accelerate further investigations on the system.
In particular different architectures can be tested to verify if a similar propulsive concept with direction control of the propelling jet could be implemented on well tested air vehicle architectures and could gradually lead to effectively optimized future air vehicle concepts which can maximise the benefits of this kind of nozzle and the consequent jet directionality.
In particular the project aims to investigate different configurations and application of this propulsion system with thrust direction control capability. Different air vehicle architectures will be investigated both by CFD simulation and experimental tests. In particular this test activity will be performed on different architectures and design concepts which can have significant advantages by the proposed propulsive architecture.
In particular, this proposed propulsive technology will be evaluated for different aerial vehicle configurations with the aims of enhancing the overall system manoeuvrability and shortening take off and landing spaces:
traditional wide-body airliner with wing mounted engines;
traditional airship bodies;
innovative concepts of aerial vehicles, with distributed or localized propulsion;
novel concepts specifically designed to maximize advantages by this directional propulsion system.
The expected results of the project are:
verification and tuning of the H.O.M.E.R. nozzle concept for aerial propulsion;
- definition of a design methodology for H.O.M.E.R. nozzle in different operative conditions, optimizing geometric parameters as a function of fluid-dynamic properties;
- analysis of feasibility of different application of the H.O.M.E.R. nozzle for aerial propulsion both on traditionally shaped air vehicles and unconventionally shaped ones;
- optimization of the H.O.M.E.R. nozzle system in the most promising configurations.
- Design and low inertia, high power/weight optimization of novel high-speed permanent magnet AC motor and electrical drive system to power the fan/compressor stages for low/high altitude operation.
These results are expected by a scientific approach involving together CFD simulations and experimental verification and validation of numerical results aiming to demonstrate the feasibility of the system and to define the possible operative methodologies and the possible limitations connected to its application.