Rotor blades

Cracks detection in welds, mounting hardwares, rivets, on blades and vanes, turbine disks, rotors blades, etc. 

In co-operation with LM Glasfiber, a complete section of a rotor blade was produced with a number of well defined defects in order to perform an initial sensitivity test by means of ultrasound, vibrations techniques and real-time radiography. Based on the results of this initial test it was found that automated ultrasonic inspection was the best suited teclmique. In co-... 

Automated ultrasonic inspection of bonded joints and laminates of rotor blades. 

Today the coin-tap test is a widely used technique on wind turbine rotor blades for inspection of thin GFRP laminates for disbonded and delaminated areas. However, since the sensitivity of this technique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, there has been an increasing demand for alternative non-destmctive testing techniques which is less operator dependent and also more sensitive to delaminations and disbonded areas situated beyond thicker GFRP-laminates. 

Fig. 1. Simple illustration of the basic design of the wind turbine rotor blade scanner.

The scanner has been constructed in modules which, for future applications, makes it easy to increase the length of the scanner for inspection of larger blades, by adding further modules to the system. In co-operation with LM Glasfiber and RIS0 it was decided to construct the first scatmer for inspection of blades with a length of max. 21m. In order to be able to scan primarily the bonded areas from the root to the tip of the rotor blade, a so-called X-unit module was constructed. The movement from the root to the tip of the blade was controlled by the P-scan system. 

Since it was required by LM Glasfiber that the scanner should be able to inspect joints between the shells and the iimer beams on each side and also the joints between the shells on the leading and trailing edge of the rotor blades, the X-Unit module was designed with three different set-ups for the Y-modules, which perform the movement of the probes transverse the length of the blade. The three different set-ups of the Y-modules are ... 

In set-up 2 the leading edge can be scanned by means of a special designed Y-module that allow the probe to follow the complex geometry of the leading edge from the root to the tip of the rotor blade. In figure 4 set-up 2 is illustrated. 

When the scanning of the adhesive bonded joint between the shells on the leading edge is complete, the rotor blade is rotated 180° and another special designed Y-module is applied for inspection of the trailing edge of the rotor blade in set-up 3, illustrated on figure 5. 

Based on a preliminary set of acceptance criteria s developed by LM Glasfiber a standard data-set has been developed for each of the above mentioned set-ups, in order to minimize the scanning time. During the performance demonstration at LM Glasfiber the effective scanning time for a complete 21m wind turbine rotor blade based on the preliminary acceptance criteria s, was found to be less than hour. 

After the performance demonstration a number of damaged rotor blades were scanned followed by a number of destructive verifications of the results achieved by ultrasonic scanning. Based on this examination it was concluded that the wind turbine rotor blade scanner is capable of detecting defects such as delaminations, inclusions, missing adhesion, lack of adhesive, porosities and variations in thickness. 

J. Rusborg, Non-Destructive inspection of wind turbine rotor blades, part I (In Danish) FORCE Institute 1995, ISBN 87-7784-049-6... 

The filter cake can then be washed either by displacement or by reslurrying. Reslurrying is easily accompHshed using the stirring action of the rotor blades when the rotor is lowered into the cake. The cake may also be dried in situ by the passage of hot air through it, or may be steam distilled for the recovery of solvent. 

The superheated steam generated in the superheater section is coHected in a header pipe that leads to the plant s high pressure steam turbine. The steam turbine s rotor consists of consecutive sets of large, curved, steel aHoy disks, each of which anchors a row of precision-cast turbine blades, also caHed buckets, which protmde tangentiaHy from the shaft and impart rotation to the shaft when impacted by jets of high pressure steam. Rows of stationary blades are anchored to the steam turbine s outer sheH and are located between the rows of moving rotor blades. 

Rotor blades also form an element of several external classifiers that are used in closed-circuit dry milhng. These are generally called mechanical air separators or classifiers. Examples are the Whirlwind classifier Sturtevant Inc.), the Gayco centrifugal separator Universal Road Machinery Co. (see Fig. 20-41), and the whizzer separator Raymond Division of Combustion Engineering Inc.). 

Some mechanical air classifiers are designed so that the fine product must pass radially inward through rotor blades instead of spirally moving across them as with whizzer blades. Examples are the Mikron separator Hosokawa Micron Powder Systems Div.), Sturtevant Side Draft separator, and the Majac classifier shown attached to the Majac jet mill (Fig. 20-55). 

An example of a typical turboexpander is shown in Fig. 29-46. Radial-flow turbines are normally single-stage and have combination impulse-reaction blades, and the rotor resembles a centrifugal-pump impeller. The gas is jetted tangentially into the outer periphery of the rotor and flows radially inward to the eye, from which the gas is jetted backward by the angle of the rotor blades so that it leaves the rotor without spin and flows axially away. 

This expansion of a condensing vapor is highly desirable thermodynamically, but the hquid must not bombard and erode the rotor blades, and, in particular, it must not accumulate in the rotor, since that would cause efficiency loss. 

To use turboexpanders for condensing streams, the rotor blades must be shaped so that their walls are parallel at every point to the vector resultant of the forces acting on suspended fog droplets (or dust particles). The suspended fog particles are thus unable to drift toward the walls. Walls would otherwise present a point of collection, interfering with performance and eroding the blades. Hundreds of turboexpanders are in successful operation involving condensing liquids. 

The reaction turbine, shown schematically in Figure 2-2, is generally more efficient. In its primary (stationary) nozzles only half the pressure energy of the gas stream is converted to velocity. The rotor with a blade speed matching the full-jetted stream velocity receives this jetted gas stream. In the rotor blades the other half of the pressure energy is used to jet the gas backward out of the rotor and, hence, to exhaust. Because half the pressure drop is taken across the rotor, a seat must be created around the periphery of the rotor to contain this pressure. Also, the pressure difference across the rotor acts on the full rotor area and creates a large thrust load on the shaft. 

As mentioned earlier, turboexpander are generally of radial reaetion turbine design beeause this geometry is often most effieient. In an ordinary impulse turbine the high veloeity stream from the nozzles makes a U-turn in the rotor blades, and this U-turn eonsumes 8%-10% of the energy. 

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