The present invention discloses a channel selection method and device and relates to the communications field, so as to resolve a problem of applying an unlicensed spectrum to a wireless cellular network. The channel selection device is configured to acquire a candidate unlicensed channel, determine an available unlicensed channel from the candidate unlicensed channel, where the available unlicensed channel is an unlicensed channel that is not interfered or on which a strength of an interference signal is less than an interference detection threshold, and acquire a first operation channel from the available unlicensed channel, where the first operation channel is a channel on which the channel selection device performs communication with user equipment in a wireless cellular network mode.

Channel selection method and device

The authors discuss a possibility to use a diverging dual-combustion chamber as applied to high-supersonic boost ramjets operating at flight Mach numbers up to Mf = 8–10. Due to diverging, this chamber allows beginning the ramjet operation from flight Mach numbers Mf ini = 2–3. The diverging combustion chamber is characterized by a ratio of its exit cross-sectional area relative to the cross-sectional area of air-intake throat. This expansion area ratio is determined at Mf = Mf ini, but it should be the same at all flight Mach numbers Mf ⇒ Mf ini, and depends on two factors: the location of a normal shock in the air-intake throat and the condition of reaching the critical velocity at the chamber exit. The dual-combustion chamber provides heat supply in its alone channel first to the subsonic flow and then, along with acceleration of the flying vehicle, to the supersonic flow, which is bound with a decrease in relative heating of working gas. Calculations of characteristics of an exemplified dual-combustion ramjet considered with a twodimensional air-intake were performed in the range of Mf = 3–7.

Characteristics of dual-combustion ramjet

Modern concepts of operation of supersonic inlets of high-velocity air-breathing engines are analyzed. It is demonstrated that the flow in the engine duct becomes extremely complicated in off-design modes of inlet operation, which can lead to unpredictable consequences, in particular, to inlet unstart. The term “inlet unstart” is considered in the present paper as a synonym of the absence of theoretical understanding and prediction of gas-dynamic phenomena. Various approaches are proposed to ensure self-regulation of the inlet-combustor system for air-breathing engines. Possible directions of further research are indicated for the purpose of stable operation of inlets in a wide range of flight conditions.

Gas-dynamic problems in off-design operation of supersonic inlets ( review )

Supersonic and hypersonic non-equilibrium flow control using laser energy deposition

Experimental research on the thermal throat of rocket based combined cycle combustor

A new dual-mode ramjet combustor concept intended for operation over a wide flight Mach number range is described. Subsonic combustion mode is similar to that of a traditional ram combustor which allows operation at higher efficiency, and to lower flight Mach numbers than current dual-mode scramjets. High speed mode is characterized by supersonic combustion in a free-jet that traverses the subsonic combustion chamber to a variable nozzle. The maximum flight Mach number of this scheme is governed largely by the same physics as its classical counterpart. Although a variable combustor exit aperture is required, the need for fuel staging to accommodate the combustion process is eliminated. Local heating from shock-boundary-layer interactions on combustor walls is also eliminated. Given the parallel nature of the present scheme, overall flowpath length is less than that of present dual-mode configurations. Cycle analysis was done to define the flowpath geometry for computational fluid dynamics (CFD) analysis, and then to determine performance based on the CFD results. CFD results for Mach 5, 8, and 12 flight conditions indicate stable supersonic free-jet formation and nozzle reattachment, thereby establishing the basic feasibility of the concept. These results also reveal the structure of, and interactions between the free-jet and recirculating combustion chamber flows. Performance based on these CFD results is slightly less than that of the constant-pressure-combustion cycle analysis primarily due to these interactions. These differences are quantified and discussed. Additional CFD results at the Mach 8 flight condition show the effects of nozzle throat area variation on combustion chamber pressure, flow structure, and performance. Calculations with constant temperature walls were also done to evaluate heat flux and overall heat loads. Aspects of the concept that warrant further study are outlined. These include diffuser design, ramjet operation, mode transition, loss mechanisms, and the effects of secondary flow for wall cooling and combustion chamber pressurization. Also recommended is an examination of system-level aspects such as weight, thermal management and rocket integration as well as alternate geometries and variable geometry schemes.

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Supersonic Free-Jet Combustion in a Ramjet Burner

A new dual-mode ramjet combustor used for operation over a wide flight Mach number range is described. Subsonic combustion mode is usable to lower flight Mach numbers than current dual-mode scramjets. High speed mode is characterized by supersonic combustion in a free-jet that traverses the subsonic combustion chamber to a variable nozzle throat. Although a variable combustor exit aperture is required, the need for fuel staging to accommodate the combustion process is eliminated. Local heating from shock-boundary-layer interactions on combustor walls is also eliminated.

Dual-mode combustor

The dual-mode free-jet combustor concept, pictured in figure 1, is described. It was introduced in 2010 as a wide- operating-range propulsion device using a novel supersonic free-jet combustion process. The unique feature of the free-jet combustor pictured in figure 1a, is supersonic combustion in an unconfined free-jet that traverses a larger subsonic combustion chamber to a variable nozzle. During this mode of operation, the propulsive stream is not in contact with the combustor walls, and equilibrates to the combustion chamber pressure. To a first order, thermodynamic efficiency is similar to that of a traditional scramjet under the assumption of constant-pressure combustion. Qualitatively, a number of possible benefits to this approach are obvious.

https://ntrs.nasa.gov/api/citations/20170008733/downloads/20170008733.pdf

Vance F. Dippold

Papers

Supersonic Free-Jet Combustion in a Ramjet Burner

Dual-mode combustor

Dual-Mode Free-Jet Combustor

Process for operating a dual-mode combustor