JPS58206807A - Control device for clearance at extremity end of rotary vane of axial flow turbine - Google Patents

Abstract

PURPOSE:To enable a clearance at the extremity end of rotary vane to be reduced and to reduce a loss of leakage by a method wherein a shroud position setting coil spring made of shape memory alloy is arranged between an annualr shroud opposed to the xetremity end of the rotary vane and a casing supporting the shroud. CONSTITUTION:An extremity end of a rotary vane 1 is positioned against a thin walled shroud 2, the shroud 2 is fixed to a casing 3 by a wedge shape seal part 4 arranged at the lower part of the casing 3. With the above arrangement, a coil spring 6 made of shape memory alloy is arranged between a thermal insulator 5 arranged outside of the shroud 2 and the casing 3. A clearance 7 at the extremity end of the rotary vane 1 expanded as an operation is started and the operation is approached to its rated operation is reduced under an extension the coil spring 6 by selecting properly a transformation point of the coil spring 6. Thereby, a loss of leakage at the extremity end of the rotary vane 1 is reduced and an efficiency of turbine is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an axial flow turbine rotor blade tip clearance control device suitable for reducing fluid loss between the rotor blade tip of the axial flow turbine and an outer cage jig.

Axial flow turbine is a general term for trickle flow type castor turbines and steam turbines. A gas turbine will be explained below as an example.

One way to improve the efficiency of gas turbines is to reduce leakage loss between turbine rotor blades and casings. The loss can be reduced by reducing the gap between the rotor blade tip and the casing. However, due to differences in the expansion coefficients and thermal mass between the casing and rotor blades, this gap is at its minimum at startup before entering rated operation, so the clearance at rated operation is the minimum that appears at startup. It was necessary to make the gap larger than the gap, leading to increased leakage loss.

Conventionally, various methods have been proposed to control the gap between the rotor blade tip and the casing.

For example, there is a method to reduce the amount of air that cools the casing during startup, causing the casing to rapidly heat and expand, and to increase the minimum gap τ prior to startup.
It is known that the shroud, which is attached to the casing and faces the tip of the rotor blade, can be forcefully moved radially outward during startup to widen the gap. However, these methods require valves and crank mechanisms, which not only complicate the structure, but also have the disadvantage of poor reliability.

An object of the present invention is to provide a rotor blade tip clearance control device for an axial flow turbine that can minimize the gap between the turbine rotor blade and the casing.

A feature of the present invention is that the radial positioning of the shroud, which is supported by the casing relative to the rotor blade tip, is performed by a coil spring made of a shape memory alloy.The shape memory alloy has a transformation temperature of 1. Taking advantage of the characteristic that the properties of metals are completely different after the martensitic transformation (martensitic transformation), above the transformation temperature the shape is memorized (in the present invention, the coil spring is stretched), and below the transformation temperature it is different. It is an alloy that exhibits a shape (fill spring in a contracted state).

In other words, by appropriately selecting the transformation temperature, the gap at the tip of the rotor blade, which widens after startup and enters rated operation, can be reduced.
5 so that the coil spring becomes smaller again as it expands (restores its shape).

Gas turbine casing temperature varies depending on location.
□ Although it is different, by changing the composition of the shape memory alloy beam, the transformation temperature can be controlled completely freely, and since this change in shape is a reversible process, it can be applied to all stages of a multistage gas turbine. Applicable.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In the figure, l is a rotor blade, and its tip tI'i faces the thin shroud 2. Shroud 2 is
A γL7 provided at the lower part of the sink 3 is attached to the casing 3 through a wedge-shaped seal portion 4. Outside K of shroud 2
Id insulation material 5 is made of shape memory alloy between the insulation material 5 and the casing 31. A fill spring 6 is provided.

Next, the operation of the invention will be explained with reference to FIGS. 1 to 3. FIG. 3 shows the relationship between the turbine rotor blade tip clearance and the operating time.

First, the operation of the coil spring 6 before it undergoes martensitic transformation will be described using FIGS. 1 and 3. Point A is the forest state before startup, and the gap 7 at the tip of the rotor blade is C0. ``When a gas turbine is started, thermal expansion of the rotor blades 1, casing 4, etc. begins due to the rise in temperature of gas passing through each part. However, the thermal expansion of the casing 4 is relatively small compared to the rotor blades Due to its low temperature, large heat capacity, etc., it tends to hit more frequently than the thermal expansion of dynamic R1.

That is, as shown in FIG. 3A-+B, the tip clearance 7 of the rotor blade 1 gradually decreases, and when the thermal expansion of the rotor including the rotor blade 1 reaches equilibrium (point B), The minimum value becomes C1. Furthermore, as the operation continues, the tip gap 7 gradually widens due to thermal expansion of the casing 3 (Figure 3 B-40).
, the initial setting value C8 of the tip clearance 7, which becomes C7 when the thermal expansion of the casing 3 reaches equilibrium (point 6), is determined from the minimum clearance C, which occurs at startup, from safety and technical viewpoints. , is determined by taking into account the relative thermal expansion difference between the casing 3 and the rotor. Now, the transformation temperature of the coil spring 6 should be made to match the temperature of the cavity 8 when the temperature of the casing 3 is constant. For example, as shown in FIG. 2, the coil spring 6 returns to its original shape, that is, in an elongated state, and can deform the thin-walled coil 2 inward in the radial direction. As a result, the third
As shown in the figure, the tip clearance 7 of the rotor blade 1 is different from that of the conventional C7
The force is reduced to C7, and the loss at the tip of the rotor blade can be reduced compared to the conventional method. 1 and 2, the wedge-shaped seal portion 4 has the function of not directly transmitting the heat of the shroud 2 that is in contact with high-temperature gas to the coil bar 6, and the wedge-shaped seal portion 4 is deformed radially inward, the shroud 2 and the casing 3
A function that prevents stress from increasing at the edges? Loaded.

According to the present invention, the gap between the tips of the rotor blades during rated operation can be reduced, so the efficiency of the turbine can be improved.

[Brief explanation of drawings]

Figures 1 and 2 show an embodiment of the present invention. Figure 1 is a cross-sectional view of the shape memory alloy before it reaches the transformation temperature. Figure 2 is a cross-sectional view of the shape memory alloy after it has reached the transformation temperature. Figure 3 is a cross-sectional view of the shape memory alloy according to the present invention. FIG. 3 is a diagram showing temporal changes in a blade tip clearance. 1... Moving blade, 2... Shroud, 3... Casing, 6... Shape memory alloy coil spring. Agent: Patent Attorney Meidai Takahashi

Claims (1)

[Claims] 1.i! 'fE? In an axial flow turbine comprising a rotor blade of an IF turbine, an annular shroud facing the tip of the rotor blade, and a casing supporting the shroud, a shape memory alloy is provided between the shroud and the casing. Made with 1. 1fL- A rotor blade tip clearance control device for a trickle flow turbine, characterized in that a shroud positioning coil spring is provided.