阅读说明：本技术 一种用于边界层转捩控制的“⊥”型凹腔结构 (Reverse T-shaped concave cavity structure for transition control of boundary layer ) 是由 禹旻 刘智勇 冯峰 杨武兵 于 2020-03-27 设计创作，主要内容包括：本发明一种用于边界层转捩控制的“⊥”型凹腔结构,该凹腔结构相比于原有凹腔结构,在底部增加了下凹腔部分,形成由上、下凹腔组合的“⊥”型凹腔结构。该凹腔结构用于转捩控制的实现方式为：首先通过数值模拟或风洞试验等手段,确定飞行器表面的转捩过程；然后将凹腔设置在需要进行流动控制的飞行器表面的转捩区上游；最后通过调整影响流动状态的重要外形参数和边界层参数达到所需的边界层转捩控制效果。本发明凹腔结构的优点在于：低压损、控制作用明显,不需要额外能量,产生噪声小。(Compared with the original concave cavity structure, the concave cavity structure is additionally provided with the lower concave cavity part at the bottom to form the inverted T-shaped concave cavity structure formed by combining the upper concave cavity and the lower concave cavity. The realization mode of the cavity structure for transition control is as follows: firstly, determining a transition process of the surface of the aircraft by means of numerical simulation or wind tunnel test and the like; then arranging the cavity on the upstream of a transition region on the surface of the aircraft needing flow control; and finally, the required boundary layer transition control effect is achieved by adjusting important appearance parameters and boundary layer parameters which influence the flow state. The concave cavity structure of the invention has the advantages that: low pressure loss, obvious control effect, no need of extra energy and low noise.)

1. A kind of reverse T type cavity structure used for transition control of boundary layer, characterized by that, it includes: an upper cavity and a lower cavity;

the upper concave cavity and the lower concave cavity form an inverted T-shaped concave cavity structure together;

the upper concave cavity and the lower concave cavity are both in rectangular structures, the length of an upper concave cavity cross section edge L1 is smaller than that of a lower concave cavity cross section edge L2, and an upper concave cavity cross section edge L1 is parallel to a lower concave cavity cross section edge L2;

the height D1 of the cross section of the upper concave cavity is greater than the height D2 of the cross section of the lower concave cavity, and the thickness of the cross section of the upper concave cavity and the thickness of the cross section of the lower concave cavity are both W;

the depth D of the inverted T-shaped concave cavity structure is D1+ D2.

2. The inverted-T cavity structure for boundary layer transition control of claim 1, wherein the inverted-T cavity structure is disposed upstream of a transition region on a surface of an aircraft, such that the inverted-T cavity structure generates a transition control effect on a downstream flow.

3. The reverse-sign-on type cavity structure for boundary layer transition control of claim 1, wherein:

L1/D1<L2/D<10，0.5<W/D<1。

4. the reverse-sign-on type cavity structure for boundary layer transition control according to any one of claims 1 to 3, wherein:

0.3<D/<1；

where is the nominal boundary layer thickness at the leading edge of the re-entrant structure.

Technical Field

The invention relates to an inverted T-shaped concave cavity structure for boundary layer transition control, belongs to the technical field of aerodynamics, and is used for boundary layer transition control.

Background

The actual fluid flow has two flow states, laminar flow and turbulent flow. The transition process from laminar flow to turbulent flow has been a hotspot and difficulty of fluid mechanics research. The friction resistance and the heat flow of a turbulent flow boundary layer are usually 3-5 times of those of a laminar flow boundary layer, the development condition of the fluid boundary layer can influence indexes such as surface friction resistance and heat transfer performance to a great extent, and the design of an aircraft is influenced, so that the method has important significance in reasonably controlling the flow characteristics of the boundary layer by adopting an active and passive flow control method.

The passive flow control has the characteristics of no need of extra energy, convenient use and reliable performance, and is a control technology which can achieve practical effects in a short period at present, and the passive control technologies mainly comprise a vortex generator, a cavity, an opening, a boundary layer forced transition device and the like. The cavity of the solid wall surface of the boundary layer can lead the flow to reach the early stage of transition, so that the downstream flow reaches a turbulent flow state. For a re-entrant flow control device, its profile parameters length-to-depth ratio coefficient L/D and width-to-depth ratio coefficient W/D affect the flow characteristics. Cavities can be divided into open, transitional and closed cavities according to their flow type: for the open cavity, the front edge shearing layer does not touch the cavity bottom surface and then crosses the cavity to collide with the rear wall; for the transitional cavity, an expansion wave and a shear layer can exist in the cavity, and the shear layer touches the bottom surface to generate a shock wave and then deviates upwards and collides with the rear wall; for the closed cavity, the airflow is accelerated to expand at the front edge to generate expansion waves, the shear layer touches the cavity bottom to form shock waves, the waves are attached to flow along the cavity bottom surface, and the airflow in front of the rear wall is lifted upwards to generate the shock waves. The aspect ratio W/D of the cavity enhances the open cavity properties.

In engineering design, how to effectively control transition and design a transition control device according to engineering requirements to effectively and reliably delay or induce the occurrence of transition is a technical problem to be solved in the art.

Disclosure of Invention

The invention mainly provides an inverted T-shaped concave cavity structure for transition control of a boundary layer, wherein a lower concave cavity part is added at the bottom of an original concave cavity to form an inverted T-shaped concave cavity flow control device formed by combining an upper concave cavity and a lower concave cavity, and the flow control device has the characteristics of low pressure loss and obvious control effect.

The technical solution of the invention is as follows:

a reverse T-shaped concave cavity structure for boundary layer transition control comprises: an upper cavity and a lower cavity;

the upper concave cavity and the lower concave cavity form an inverted T-shaped concave cavity structure together;

the upper concave cavity and the lower concave cavity are both in rectangular structures, the length of an upper concave cavity cross section edge L1 is smaller than that of a lower concave cavity cross section edge L2, and an upper concave cavity cross section edge L1 is parallel to a lower concave cavity cross section edge L2;

the height D1 of the cross section of the upper concave cavity is greater than the height D2 of the cross section of the lower concave cavity, and the thickness of the cross section of the upper concave cavity and the thickness of the cross section of the lower concave cavity are both W;

the depth D of the inverted T-shaped cavity structure is D1+ D2;

the inverted T-shaped cavity structure is arranged at the upstream of a transition region on the surface of the aircraft, so that the inverted T-shaped cavity structure generates a transition control effect on downstream flow.

L1/D1<L2/D<10，0.5<W/D<1。

0.3< D/<1, where is the nominal boundary layer thickness at the leading edge of the re-entrant structure.

Compared with the prior art, the invention has the advantages that:

1) the invention has small modification amount on the original concave cavity control device and does not conflict with the original important parameter influencing transition control;

2) under the condition of the same depth as the original concave cavity control device, the transition control effect of the inverted T-shaped concave cavity transition control device is more obvious;

3) compared with the original concave cavity control device, the reverse T-shaped concave cavity has the advantages of small self-excited oscillation and low noise.

Drawings

FIG. 1 is a schematic diagram of a cavity structure of the present invention in comparison to a conventional cavity structure;

FIG. 2 is a side view of the bowl structure of the present invention;

FIG. 3 is a top view of the cavity structure of the present invention;

FIG. 4 is the evolution of boundary layer thickness with downstream;

FIG. 5 is a transition from laminar flow to turbulent flow on a plate;

FIG. 6 is a variation of the mean flow velocity profile downstream of the cavity;

FIG. 7 is a variation of the unstable region downstream of the cavity;

FIG. 8(a) FIG. 8(b) FIG. 8(c) is the evolution of different perturbations with downstream;

figure 9 root mean square pressure at the bottom of the cavity.

Detailed Description

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

1) As shown in fig. 1, the invention is a reverse T-shaped concave cavity structure, which is composed of an upper concave cavity and a lower concave cavity, wherein the lengths and the depths of the upper concave cavity and the lower concave cavity are shown in fig. 2, and the width of the concave cavity is shown in fig. 3;

2) obtaining the flow condition of the aircraft according to working conditions such as incoming flow Mach number, Reynolds number, wall temperature and the like by means of numerical simulation, wind tunnel test and the like, and calculating the thickness of the boundary layer;

3) if the numerical simulation is carried out, the transition process is simulated in modes of obtaining unstable disturbance of an inlet through linear stability analysis, adding white noise at the inlet, introducing suction disturbance in wall blowing and the like; if the test is a wind tunnel test, a transition process is obtained through a measurement technology;

4) placing an inverted T-shaped cavity transition control device at the upstream of a transition region;

5) by adjusting the upper cavity length-depth ratio coefficient L1/D1, the lower cavity length-depth ratio coefficient L2/D2, the cavity width-depth ratio coefficient W/D and the boundary layer thickness-to-cavity depth ratio coefficient/D, a superior transition control effect is achieved.

Specifically, the present invention relates to an inverted-t type cavity structure for boundary layer transition control, including: an upper cavity and a lower cavity;

the upper concave cavity and the lower concave cavity form an inverted T-shaped concave cavity structure together;

the upper concave cavity and the lower concave cavity are both in rectangular structures, the length of an upper concave cavity cross section edge L1 is smaller than that of a lower concave cavity cross section edge L2, and an upper concave cavity cross section edge L1 is parallel to a lower concave cavity cross section edge L2;

the height D1 of the cross section of the upper concave cavity is greater than the height D2 of the cross section of the lower concave cavity, and the thickness of the cross section of the upper concave cavity and the thickness of the cross section of the lower concave cavity are both W;

the depth D of the inverted T-shaped cavity structure is equal to the sum of the depths of the upper concave cavity and the lower concave cavity, namely D1+ D2.

The inverted T-shaped cavity structure is arranged in a laminar flow region on the surface of the aircraft, namely the cavity needs to be arranged at the upstream of a transition region on the surface of the aircraft, so that the inverted T-shaped cavity structure generates a transition control effect on downstream flow.

The shape parameters of the concave cavity are designed as follows:

(1) the ratio coefficient L1/D1 of the length of the upper cavity to the depth, the ratio coefficient L2/D2 of the length of the lower cavity to the depth, and the ratio W/D of the width and the depth of the whole cavity are parameters influencing the transition control of the boundary;

(2) according to the reasonable control of the surface of the aircraft on the processing device, the size of the concave cavity is not suitable to be too large, and the size of the reverse T-shaped concave cavity is recommended to be controlled to be L1/D1< L2/D <10, and 0.5< W/D < 1.

The nominal boundary layer thickness at the leading edge of the cavity, which is the height perpendicular to the wall from the boundary layer wall to the point where the flow velocity along the wall tangent reaches 99% of the free incoming flow velocity, has a significant effect on the cavity flow, affecting the development of a free shear layer, affecting the pressure distribution of the bottom cavity.

The ratio coefficient D/of the cavity depth and the boundary layer thickness can be used as a key parameter for transition control result analysis, and 0.3< D/<1 is suggested according to the research on the influence relationship between the transition device and the boundary layer.