CN111237085B

CN111237085B - Turbine engine primary and secondary flow combined variable circulation method

Info

Publication number: CN111237085B
Application number: CN202010183525.9A
Authority: CN
Inventors: 丁水汀; 刘传凯; 邱天; 李果
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2020-03-16
Filing date: 2020-03-16
Publication date: 2021-05-14
Anticipated expiration: 2040-03-16
Also published as: CN111237085A

Abstract

The invention discloses a turbine engine primary and secondary flow combined variable circulation method, which enables a core machine flow path to respectively realize a turbojet mode secondary flow refrigeration cycle and a turbofan mode inner duct Brayton cycle in high-speed flight and low-speed flight states through mode switching of a variable circulation mechanism. Therefore, under a high-speed flight mode, the quality of secondary flow cold air is greatly improved, and ultrahigh turbine front temperature and an ultra-wide speed range are realized. In a low-speed flight mode, the ultrahigh bypass ratio and the ultralow oil consumption rate are realized by utilizing the huge flow difference between the fan and the air compressor. The invention breaks through the limit of the speed range of the existing turbine engine and gives consideration to the requirement of long voyage.

Description

Turbine engine primary and secondary flow combined variable circulation method

Technical Field

The invention relates to a turbine engine, in particular to a turbine engine primary and secondary flow combined variable cycle method.

Background

In the design of an airplane with both a wide speed range and a long range, a power device is crucial: the wide speed range requires a small bypass ratio, a low pressure increase ratio and a high turbine front temperature; the long voyage requires large bypass ratio, high pressure increase ratio and moderate turbine front temperature. Variable cycle engines are promising power plants to achieve these conflicting requirements. In the 60's of the 20 th century, the american general electric company first proposed the concept of a Variable Cycle Engine (VCE) intended to combine the technical advantages of both turbojet and turbofan engines, with the aim of realizing both turbojet and turbofan cycles on the same engine. To date, VCE technology has been explored for nearly 60 years and has developed its course. And aiming at the requirements of supersonic transport airplanes and fighter power systems, variable-cycle technical schemes such as double-culvert and three-culvert self-adaptive variable cycles based on different geometric adjustment methods are developed.

According to the working principle of the turbine engine, the three most important parameters influencing the further improvement of airspace, speed range and efficiency index of the aviation gas turbine engine are bypass ratio, total pressure increase ratio and turbine front temperature. However, the existing variable cycle engine is limited by the technical route, the bypass ratio adjusting range of the engine can be changed only in a small range, the engine supercharging ratio adjusting range is expanded, the temperature before the turbine is increased, and the speed range of the variable cycle engine cannot be effectively increased and the cycle efficiency cannot be improved. In general, the limitations of conventional variable cycle engines are manifested in two ways:

(1) aiming at the requirement of high-speed flight, the range of the working pressure ratio cannot be effectively widened and the total temperature before the turbine cannot be improved, so that the range of a speed domain and an airspace is limited. In order to ensure low-speed economy, a traditional variable-cycle engine adopts a high designed pressure ratio, and a technical route based on the bypass variable geometry is not capable of effectively adjusting the power cycle pressure ratio, so that the heating capacity of a combustion chamber is insufficient during high-speed flight, as shown in fig. 1, and the cyclic power of the high-speed flight of the engine is insufficient and the thrust is too early and too fast to attenuate. Therefore, in order to break through the speed range limit of the traditional variable cycle engine 3.2Ma, the temperature level before the turbine is increased while the pressure ratio range of the compressor is greatly widened.

(2) Aiming at the requirement of low-speed flight, the working pressure increase ratio and the bypass ratio cannot be effectively improved, so that the reduction amplitude of the low-speed oil consumption rate is limited. The traditional variable-cycle engine is used for expanding a speed range, and a turbojet power cycle is needed during high-speed flight. Due to the limitation of the size of the casing and the limitation of the outer-duct variable geometry technology, the limit change amplitude of the duct ratio cannot exceed 1.3, and the pressure increase ratio cannot be effectively adjusted, so that the cyclic thermal efficiency and the propulsion efficiency during low-speed flight cannot be effectively improved, as shown in fig. 2 (in fig. 2, T is T₀Is ambient temperature, T₂For the outlet temperature, T, of the compressor of a conventional variable cycle engine_2.iAt a desired compressor outlet temperature). Therefore, in order to remarkably reduce the low-speed oil consumption rate of the traditional variable-cycle engine and break through the range limit, the supercharging ratio of the engine must be improved while the bypass ratio of the engine is greatly increased.

In conclusion, the traditional variable cycle engine technical route mainly based on the ducted geometry adjustment has the problems that the adjustable ducted ratio range is limited, the adjustable supercharging ratio range and the turbine front temperature upper limit are difficult to enlarge 'pain spots', and the speed range, the airspace range and the range limit of the variable cycle engine are greatly limited. Therefore, the traditional circulation changing thought and method must be subverted from the source, and a new concept, a new principle and a new scheme are provided, so that the airspace and speed domain limit of the traditional turbine engine can be hopefully broken through, and the long-range requirement is considered.

Disclosure of Invention

In order to break through the performance bottlenecks of the variable-cycle engine in the speed range, the airspace and the oil consumption rate, and aiming at the 'pain point' of the existing variable-cycle engine with adjustable bypass ratio, adjustable range of pressure ratio and limited temperature in front of a turbine, the invention provides a turbine engine primary and secondary flow combined variable-cycle method, which changes the traditional variable-cycle thought and method from the source, can greatly break through the adjustable range limit of the cycle parameters of the variable-cycle engine, and realizes the consideration of speed range crossing and long voyage.

The invention relates to a turbine engine secondary flow combined variable cycle method, which is characterized in that under a high-speed flight mode, airflow flowing through an air inlet and a fan is divided into two parts, namely airflow A and airflow B. Wherein the gas stream A enters directly into the combustion chamber of the turbine engine and flows through the low pressure turbine and the tail pipe in sequence; therefore, the air inlet, the fan, the combustion chamber, the low-pressure turbine and the tail nozzle jointly form a Brayton cycle of primary flow, and thrust is generated. The airflow B is used as cold air of a secondary flow air system, and after the cold air passes through a high-pressure air compressor, an air-air heat exchanger and a high-pressure turbine in sequence to form a cold air refrigeration cycle, the part entering the high-pressure air compressor is cooled.

In the low-speed flight mode, the airflow flowing through the air inlet and the fan is divided into two paths; similarly, the air flow A and the air flow B are respectively; wherein the air flow a is directed directly to the bypass. The airflow B firstly flows into the high-pressure compressor, is pressurized by the high-pressure compressor and then directly enters the combustion chamber; the airflow at the outlet of the combustion chamber firstly enters a high-pressure turbine to expand and do work, and then enters a low-pressure turbine.

The invention has the advantages that:

1. the turbine engine primary and secondary flow combined variable circulation method can realize large-range adjustment (0-4) of the bypass ratio of the engine, large-range adjustment (2-40) of the pressure ratio and large-range increase (2400K) of the front temperature limit of the turbine

2. The turbine engine primary and secondary flow combined variable cycle method can enlarge the theoretical speed range of the variable cycle turbine engine from (0-3.2Ma) to (0-5 Ma);

3. the turbine engine primary and secondary flow combined variable-cycle method can reduce the subsonic cruising oil consumption rate of the variable-cycle turbine engine by more than 15%.

Drawings

FIG. 1 is a schematic diagram of a conventional variable cycle engine speed range limitation;

FIG. 2 is a schematic diagram of limited thermal efficiency of a conventional variable cycle engine;

FIG. 3 is a schematic view of the high-speed flight mode of the turbine engine employing a secondary flow combined variable cycle according to the present invention;

FIG. 4 illustrates the principle of the present invention for increasing the cyclic power of the turbine engine in a high-speed flight mode by combining a secondary flow and changing the cycle;

FIG. 5 is a schematic view of the low speed flight mode of the turbine engine using a secondary flow combined variable cycle according to the present invention;

FIG. 6 is a schematic diagram of the thermal efficiency enhancement principle of the low speed flight mode of the turbine engine using a secondary flow combined variable cycle according to the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

The invention relates to a turbine engine primary and secondary flow combined variable cycle method, which designs a compression system in a turbine engine by adopting a high-flow fan with a low designed pressure ratio and a low-flow core high-pressure compressor with a high designed pressure ratio. Meanwhile, under the high-speed state and the low-speed state, different thermodynamic cycle modes are respectively designed so as to meet the requirements of ultrahigh speed and long voyage. The thermodynamic cycle modes in the two modes of operation are specifically as follows:

A. high speed flight mode (turbojet mode, Ma > 1.5).

The air flow through the inlet and fan is designed to be split into two streams, with the fan last stage most (about 80%) entering the combustion chamber of the turbine engine directly and passing through the low pressure turbine and the jet nozzle in sequence. Thus, the air inlet, the fan, the combustion chamber, the low-pressure turbine and the tail nozzle jointly form a Brayton cycle of primary flow to generate thrust.

The last-stage small part of airflow (about 20%) of the fan is used as the cold air of the secondary flow air system, and after the cold air passes through the high-pressure compressor, the air-air heat exchanger and the high-pressure turbine in sequence to form a cold air refrigeration cycle, the quality and the cooling effect of the cold air are greatly improved, as shown in fig. 3. The power required by the secondary flow cold air refrigeration cycle is extracted from the primary flow cycle through the variable speed drive device. Through the design, the engine becomes a turbine engine with low supercharging ratio and high turbine front temperature in a high-speed flight mode.

Since only the fan is involved in the primary flow compression process in the high speed flight mode, the boost ratio of the engine can be significantly lower than that of a conventional variable cycle engine. Meanwhile, the quality of the cold air is greatly improved due to the secondary flow refrigeration cycle, and the temperature in front of the turbine higher than that of a conventional variable-cycle engine can be realized under the same material level. Thus, in the high speed flight mode, the engine will achieve higher cycle work than a conventional variable cycle engine, as shown in FIG. 4. Moreover, the low pressure ratio of the high-speed mode of the engine is also beneficial to increasing the flow capacity of the high-speed flight of the engine, and further the high-speed thrust and the speed range are greatly improved. Through performance evaluation, the engine can support super-high-speed cruising with the maximum speed of 5Ma under the condition of no force application.

B. Low speed flight mode (turbofan mode, Ma < 1.5).

Mode switching of a variable cycle mechanism comprising a mode switching valve, an adjustable duct ejector and the like (refer to the research status of a variable cycle engine adjusting mechanism [ J ] aviation power, 2019(04):43-46.) is realized by making most of the last-stage airflow (nearly 80%) of a fan not directly enter a combustion chamber and directly guide the airflow to an external duct;

a small part of air flow (about 20%) at the last stage of the fan firstly flows into the high-pressure compressor, is pressurized by the high-pressure compressor and then directly enters the combustion chamber; the airflow at the outlet of the combustion chamber firstly enters the high-pressure turbine to be expanded and do work, and then enters the low-pressure turbine, as shown in fig. 5. Through the design, the high-pressure compressor and the high-pressure turbine are converted into a component of a primary flow inner duct Brayton cycle from a component of a secondary flow refrigeration cycle.

Under the low-speed flight mode, the airflow flow flowing to the outer duct is more than 4 times of the airflow flow of the inner duct (equivalent to a large-duct-ratio turbofan engine with a duct ratio of more than 4), and far exceeds the limit that the adjustable duct ratio of the conventional variable-cycle engine is 1 at most, so that the propelling efficiency during low-speed flight is greatly improved. Furthermore, in the low-speed flight mode, the fan and the compressor participate in the primary flow compression process, the total pressure ratio of the engine can exceed 30, and therefore, the thermal efficiency of the turbofan cycle is also obviously higher than that of the conventional variable cycle engine, as shown in fig. 6. This will greatly improve the economy of the low speed flight mode of the engine. Through performance evaluation, the voyage of the scheme of the advanced cycle-variable engine is improved by more than 15% compared with that of a foreign advanced cycle-variable engine under the subsonic cruising state of 11 kilometers and 0.8 Ma.

Claims

1. A turbine engine primary and secondary flow combined variable cycle method is characterized in that:

in a high-speed flight mode, the airflow flowing through the air inlet and the fan is divided into two paths, namely airflow A and airflow B; wherein the gas stream A enters directly into the combustion chamber of the turbine engine and flows through the low pressure turbine and the tail pipe in sequence; therefore, the air inlet, the fan, the combustion chamber, the low-pressure turbine and the tail nozzle jointly form a Brayton cycle of primary flow to generate thrust; the airflow B is used as cold air of a secondary flow air system, sequentially passes through a high-pressure compressor, an air-air heat exchanger and a high-pressure turbine to form a cold air refrigeration cycle, and then is used for cooling a hot end part of the high-pressure turbine blade;

in the low-speed flight mode, the airflow flowing through the air inlet and the fan is divided into two paths; similarly, the air flow A and the air flow B are respectively; wherein the air flow A is directly directed to the outer duct; the airflow B firstly flows into the high-pressure compressor, is pressurized by the high-pressure compressor and then enters the combustion chamber; the airflow at the outlet of the combustion chamber firstly enters a high-pressure turbine to expand and do work, and then enters a low-pressure turbine.

2. The turbine engine secondary flow combined variable cycle method as claimed in claim 1, wherein: a high-flow fan with low designed pressure ratio and a core compressor with high designed pressure ratio and low flow rate are adopted to form a compression system in the turbine engine, and the high-pressure compressor and the high-pressure turbine can be mutually converted between a component of a primary flow inner duct Brayton cycle in a low-speed flight mode and a component of a secondary flow refrigeration cycle in a high-speed flight mode.

3. The turbine engine secondary flow combined variable cycle method as claimed in claim 1, wherein: in the high-speed flight mode, the secondary flow cold air is cooled through the cold air refrigeration cycle, and the cold air quality of the engine and the temperature in front of the turbine are improved.

4. The turbine engine secondary flow combined variable cycle method as claimed in claim 1, wherein: in the high-speed and low-speed flight modes, the air flow A and the air flow B respectively account for about 80% and 20% of the total air flow.