A variable-geometry turbocompressor is provided which includes a tandem variable stator downstream of a rotor stage. The tandem stator includes an inlet stator cascade and an outlet stator cascade arranged adjacent one another and each including variable guide vanes. To accommodate precise control of the air flow over various compressor operating conditions, the inlet and outlet stator cascades are provided with adjusting mechanisms for varying the position of their vanes independently of one another.

This invention relates to a variable-geometry turbocompressor having at 
least one variable inlet stator upstream of the first rotor stage. 
A turbocompressor of said generic category is known form DE-OS 25 02 986. 
The variable inlet stator of this known arrangement exhibits two separate 
stator cascades arranged one downstream of the other (tandem construction) 
the vanes of which permit of separate pivotal variation. This serves to 
achieve the great amount of deflection of the gas stream and, thus, the 
great amount of preswirl required for certain operating regimes. 
In a broad aspect of the present invention the off-design performance of a 
compressor forming part of a gas generator is improved to especially 
provide good adaptation to the following design and operating 
requirements: 
compressors of high compression ratio with correspondingly high 
requirements for the adaptability of the forward stages to the greatly 
fluctuating air flow in the compressor inlet section. 
Cooperation of the compressor with heat exchanger and mechanically 
independent, variable power turbine, compelling the compressor working 
line to be relatively high in the lower speed range to cater to the 
off-design performance of the gas turbine. 
This requires that the airflow in the compressor inlet section and the 
rotational speed of the compressor be correlated; a requirement that 
cannot be achieved using an arrangement of the known type, i.e., a tandem 
inlet stator the inlet row of vanes of which is indeed variable separately 
from the outlet row of vanes, but only and invariably in the same 
direction and in a given relation to it. 
It is a particular object of the present invention to provide a 
turbocompressor of said generic category, where the first rotor stage is 
directly followed by a variable stator which in conventional arrangement 
embraces two separate stator cascades essentially arranged one downstream 
of the other (tandem construction) and the separate inlet stator cascade 
of which is variable independently of the separate outlet stator cascade. 
In a further aspect of the present invention the second or further rotor 
stages too are fitted at their downstream end with variable tandem stators 
the separate inlet stator cascade of which is variable independently of 
the separate outlet stator cascade. 
The independence with which the separate inlet stator cascade(s) of the 
tandem stator(s) can be actuated permits excellent adaptation of the 
compressor to off-design operation of a gas generator and permits a safe 
surge margin to be achieved also in transient operation by suitable 
control provisions, while at normal operating conditions, maximum 
efficiency can be achieved with the aid of suitable control provisions. It 
is especially during acceleration of the gas generator, in the presence of 
pressure or temperature distortions at the inlet, of bleed air and/or 
mechanical power takeoffs that individual variability of the separate 
inlet stator cascade(s) ensures optimum adaptation of the compressor to 
the respective operating regime. 
In a further aspect of the present invention the two-parameter actuation of 
the tandem stator(s)--other conditions remaining the same--enables the 
maximum allowable afflux angle to be widened by moderately closing the 
separate inlet stator cascade with the position of the separate outlet 
stator cascade remaining unchanged, and simultaneously, the maximum 
allowable aerodynamic load to be augmented and the stall margin to be 
widened by widening the gap between the inlet vanes and outlet vanes. 
Two-parameter control ultimately affords more design latitude in the 
interest of improved aerodynamic load capacity of a compressor in 
steady-state operation, because individual actuation of the vanes in the 
inlet stator and the tandem stators permits the vane geometry to be 
optimized primarily for optimum efficiency at low surge margin and 
secondarily--with a different setting of the tandem stators--for, e.g., 
maximum surge margin or maximum insensitivity to inlet distortions. 
In a further advantageous aspect of the present invention at least two 
further compressor stages downstream of the variable tandem stator(s) are 
fitted with variable single stator cascades, considering that when 
extending the actuating range of the forward stator, aerodynamically 
optimum correspondence of downstream stator cascades were prevented when 
these had fixed vanes. The inlet stator and the single stator cascades of 
the rotor stages downstream of the forward stages can then be actuated in 
response to the same actuating parameters as the separate outlet stator 
cascade(s) of the tandem stator(s). 
In a further advantageous aspect of the present invention the separate 
inlet stator cascade of the tandem stator is connected to the separate 
outlet cascade such that codirectional actuation of these two cascades is 
in response to a first actuating parameter and that it is additionally 
variable by means of a higher-authority actuating element. This 
arrangement provides an advantage in that in many cases when the operating 
regime of the compressor or gas generator changes, only a single actuating 
motion will be required, so that in these cases the higher-authority 
actuating element does not need motivating. 
A preferred version of a turbocompressor arranged in accordance with the 
present invention is characterized by a stator actuating mechanism having 
an actuating shroud for each row of vanes, pivotally connected to which 
shroud are the stator vanes by means of links, the shrouds themselves 
being rotatably variable by means of a central first actuating rod 
operated through an actuating element, and characterized in that a second 
actuating rod with a separate actuating element is provided for the 
separate inlet cascade of the tandem stator(s). 
Coupling of the two actuating rods one with the other for codirectional 
actuation can be effected such that the two actuating rods are carried on 
the same pivotal axis and the actuating element of the second actuating 
rod is arranged on the first actuating rod. In an alternative arrangement 
both actuating elements are pivotally connected to the compressor casing, 
where if codirectional actuation of the two cascades through a first 
actuating element is desired, the actuating element for the second 
actuating rod is carried via a pivot that is fixedly arranged on the first 
actuating rod.

The turbocompressor illustrated in FIG. 1 in an axial, fragmentary view has 
a rotor 20 and a compressor case 10. The axis of rotation of rotor 20 is 
indicated by the numeral 21. The first three stages of the rotor 20 are 
indicated by the numerals 2, 4 and 6. The first rotor stage 2 is preceded 
by an inlet stator 1 in tandem construction embracing the separate stator 
cascades 11, 12 one downstream of the other, and it is succeeded by a 
tandem stator 3 embracing a separate inlet stator cascade 31 and a 
separate outlet stator cascade 32. The second rotor stage 4 and the third 
rotor stage 6 are each succeeded by single but variable stator cascades 5 
and 7. The various stator vanes of the separate stator cascades 11, 12 are 
connected to actuating shrouds 15, 16 through links 13, 14 such that 
rotation of the shrouds 15, 16 about the central axis 21 of the compressor 
produces pivotal movement of the vanes in the separate cascades 11, 12. 
The vanes in the separate stator cascades 31, 32 are similarly pivotally 
connected to the shrouds 35, 36 through links 33, 34; and the vanes in the 
variable stator cascades 5 and 7 to actuating shrouds 55, 75 through links 
54, 74. The links 14, 34 are shorter than the links 13, 33, respectively, 
so that an approximately equal amount of rotation of the actuating shrouds 
15, 16 and 35, 36, respectively, produce a wider pivotal movement of the 
respective separate outlet stator cascades 12, 32 referred to the pivotal 
movement of the separate inlet stator cascades 11, 31. 
FIG. 2 shows the arrangement of FIG. 1 in plan view and illustrates a first 
actuating mode for rotating the actuating shrouds 15, 16, 35, 36, 55, 75. 
In this arrangement the actuating shrouds 15, 16, 36, 55 and 75 are 
pivotally connected to a first common actuating rod 103 through 
corresponding links 17, 18, 38, 57 and 77. 
This actuating rod 103 is arranged for pivotal movement about a pivotal 
axis 104 and is pivotally moved by means of a piston 102 of an actuator 
101. As it will be readily apparent the separate stator cascades 11, 12 of 
the inlet cascade 1, the separate outlet stator cascade 32 of the 
succeeding stator 3 and the single stator cascades 5 and 7 are all 
actuated codirectionally when the actuator 101 is operated. For the 
separate inlet stator cascade 31, a second actuating rod 113 with its own 
linear actuator 111 and actuating piston 112 is provided. The actuating 
shroud 35 of the separate stator cascade 31 is pivotally connected to the 
second actuating rod 113 through a link 37. While the second actuating rod 
113 is carried on the same pivotal axis 104 as the first actuating rod 
103, the two actuating rods are pivoted in complete independence of each 
other, which is achieved by dissimilar motivation of the actuators 101, 
111. Both actuators are supported on the compressor casing 10. 
Optionally arranged in lieu of the single downstream cascades 5, 7 
following the rotor stages 4 and 6 are tandem stators of the same 
construction as downstream stator 3, in which case the inlet cascades of 
all downstream tandem stators are actuated by the second actuating rod 
113. 
This optional embodiment is depicted in FIGS. 1A and 2A, wherein like 
reference numerals as in FIGS. 1 and 2 are used for like structures. The 
second sets of stators and the adjusting mechanisms are depicted by the 
reference characters 54A, 55A, 74A and 75A. 
As it will be readily apparent the embodiment in FIG. 3 differs from the 
basic embodiment in FIG. 2 by the actuating motion of the actuator 111 not 
being transmitted directly to the the second actuating rod 113, but via a 
pivot 105 fixedly arranged on the first actuating rod 103. Use of a 
bellcrank 106 between the piston rod of the piston 112 and the second 
actuating rod 113 supported on pivot 105 enables the second actuating rod 
113 to go through an equally directed and almost equally wide pivotal 
movement as the same actuating rod 103. However, since the actuator 111 
should on the other hand be driven independently of the actuator 101, the 
actuating shroud 35 and with it the separate inlet stator cascade 31 of 
the tandem stator 3 can still be actuated independently of the other 
variable stators. The advantage afforded by this embodiment is that a need 
to drive the actuator 111 exists only when a pronounced deviation of the 
actuating motion of the separate inlet stator cascade 31 of the tandem 
stator 3 from that of the remaining stators is required, whereas in the 
remaining operating cases the need to drive this actuator is eliminated. 
This similarly applies to the further embodiment of the invention 
illustrated in FIG. 4. This embodiment differs from the second embodiment 
of FIG. 3 merely in that the actuator 111 is no longer pivotally connected 
to the compressor case 10 but is completely arranged on the first 
actuating rod 103. When the actuator 101 is operated, therefore, the 
second actuating rod 113 goes through the same pivotal motion as the first 
actuating rod 103. In this respect the actuation of all variable stators 
is in response to a single parameter. It is only when a deviation from 
one-parameter actuation is desired for the separate inlet stator cascade 
31 of the tandem stator 3 that the actuator 111 is motivated, which in 
turn is connected to the second actuating rod 113 through a bellcrank 106. 
In this manner the position of the separate inlet stator cascade 31 of the 
tandem stator 3 can be adjusted independently of the other variable 
stators.