Integral Tuned Mass Absorber for Turbine Blades
Mechanical and Fluid Systems
Integral Tuned Mass Absorber for Turbine Blades (MFS-TOPS-111)
Additive manufacturing enables novel turbine blade and blisk designs
Overview
NASA’s Marshall Space Flight Center has developed a novel turbine blade design and manufacturing approach that provides a significant reduction in turbine blade resonant vibration. In particular this innovation addresses the unique resonance vibration challenges of conventionally machined turbine bladed-discs, or blisks. The design approach includes an internal blade tuned mass absorber structure that can be placed at optimal location where deflection is greatest. Additive manufacturing is used to make this unique structure. Prototypes have demonstrated a 50% reduction in resonant vibration. Importantly, the innovation also enables improved predictive modelling of the resonant behavior of new blisk designs because the tuned-mass absorber acts as a linear system. In contrast, modelling of conventional blade dampers is extremely complex and therefore requires an expensive iterative test program dedicated to validation of the damper design.
The Technology
Additive manufacturing methods (e.g. Laser Metal Sintering) are used to integrally fabricate a tuned-mass vibration absorber inside a turbine blade. The design approach uses an internal column manufactured as part of the blade that is optimized such that the dynamics of the blade damper system are rearranged and reduced according to the well-known science of tuned mass-absorption (TMA). The TMA concept has been implemented successfully in applications ranging from skyscrapers to liquid oxygen tanks for space vehicles. Indeed, this theory has been conceptually applied to bladed-disk vibration, but a practical design has not previously been reported.
The NASA innovation addresses another important challenge for turbine blade vibration damper designs. All existing blade damper solutions are essentially incapable of being reliably predicted, so an expensive post-design test program must be performed to validate the expected response. Even then, the actual magnitude of the response reduction under actual hot fire conditions may never be known. The dynamic response of this tuned-mass-absorber design is both substantial and can be analytically predicted with high confidence, and thus the response can be incorporated fully into the up-front design process.
Benefits
- Effective: Prototype designs and tests have demonstrated 50% reduction in vibration.
- Inexpensive: Use of additive manufacturing enables Tuned Mass Absorber to be fabricated simultaneously with blade at no extra cost.
- Response reduction can be implemented into up-front design: Linear design allows accurate prediction of blade response without costly test program.
- Applicable to Multiple Modes: each tuned-mass-absorber targets two modes, and multiple absorbers can be used in each blade.
- Reliable: Design will not lock-up or potentially introduce foreign-object-debris like conventional blade dampers.
Applications
- Rocket engine turbopumps
- Jet engines
- Land-based gas turbines for power generation
- APU’s and turbochargers
- All components in turbomachine flow-path (impellers, stators, vanes).
Similar Results
Anti-Phase Noise Suppression Rotor Technologies
Rotor noise and vibration are two sources of operational challenges for all aircraft operating with open rotors such as helicopters, unmanned aerial vehicles (UAVs), urban air mobility personal air vehicles, drones, and aircraft operating with ducted fans such as passenger aircraft. One disadvantage of convention rotor design is the noise due to noise-induced shed vortices generated by rotor blades. The unique problem with rotor noise and vibration is the periodic blade passage that causes a harmonic reinforcement and causes the rotor blades to vibrate and generate noise sources. This technology from NASA Ames seeks to optimize the implementation of anti-phase trailing edge designs and asymmetric blade tip treatments for rotor noise suppression and integrated aircraft noise solutions by incorporating the anti-phase rotor design concepts into an aircraft flight control system to reduce noise footprint. There are several embodiments of the invention, which include the following: (1) an anti-phase trailing edge design whereby the trailing edge pattern of the leading rotor blade is offset by a phase shift from the trailing edge pattern of the following blade; (2) an anti-phase rotor design implementing asymmetric blade tips with inverted airfoil; and (3) other anti-phase enabled concepts such as unequal blade length, ducted rotors with non-radial unequally spaced struts, and multi-axis tilt rotor design incorporating the anti-phase rotor design.
A New Twist Makes Rotating Machinery More Efficient and Quieter
Derived from a design approach for a new wing known as PRANDTL-D, this technology achieves similar improvements for propellers and other rotating machinery.
How It Works
To achieve the innovation's alternate spanload, Armstrong designers applied a non-linear twist to the propeller blade. The twist moves the load inward and dissipates the tip vortex over a wider area, minimizing its effect on drag. It also results in a decrease in load at the tip and reduced torque at the tip. These changes combine to achieve a dramatic reduction in power consumption without compromising the blade's other parameters. Specifically, the blade's diameter and rpm remain unchanged.
What Makes It Better
Unlike the conventional minimum induced loss (elliptical) spanload, which consumes large amounts of power at the tip of the blade, the new design unloads the tip and reduces torque, achieving significant improvements in efficiency. First-order analysis shows a more than 15 percent improvement in power consumption while producing the same thrust. The design also produces significantly less noise than conventional blade designs.
Axial Magnetic Flux Airflow Integrated Compressor-Generator-Motor Turbojet
The innovation uses the rotating blades of the compressor section to act as structural support for the generator. Since the compressor is the coolest part of the engine, it will reduce the potential for interference with magnetics and associated curie points of the permanent magnets. The placement of the generator in the cooler part of the engine flowpath (fan or compressor) will also improve the electrical insulation system's degradation and serve to improve overall system lifetime.
The configuration proposed by Armstrong's design would be an axial magnetic flux permanent magnet generator or motor. The electrical/mechanical interface could serve to deliver power to the shaft of the turbojet/fan or extract power from the shaft.
This axial electromagnetic flux design is more efficient for the combined function of aero-thermal heat transfer and generation of electricity. This is due to the relative amount of available cooling surface area, which has an advantage over radial designs given the total system volumetric aspect ratio of the generator/compressor section. When the system is viewed as a thermodynamic cycle, it is more efficient because it is essentially a regenerative cycle, with the heat of generation being fed back into the cycle instead of being released into the ambient surroundings
Reverse Vortex Ring (RVR)
Vibration problems, which occur more frequently in high power to weight machines, often lead to costly down time, subsequent redesign, and, in some instances, catastrophic failure. A disproportionate number of vibration problems in rotating machinery can be attributed to highly pre-swirled fluid entering tight clearance locations such as seals and fluid bearings. The relationship between high fluid pre-swirl and undesirable vibration issues is clear. Machines with high levels of fluid pre-swirl are more susceptible to instabilities and vibration problems.
A top priority in rotor dynamic design, therefore, is to develop devices to minimize the level of fluid pre-swirl entering tight clearance locations. The RVR was designed to condition the flow prior to entering the seal (or axial flow fluid-film bearing) so that the flow through the annular clearance is at a minimum purely axial. While conventional swirl brakes have only been shown to reduce pre-swirl by up to 30%, the RVR can actually reverse the direction of the swirl, so that circumferential fluid velocity flows in a direction counter to shaft rotation. Thus, a classic detriment to rotating machinery has now become an asset to ameliorate vibration issues through the RVR.
The RVR is axially efficient, typically increasing the axial length of a smooth annular seal on the order of 10-12%.
The RVR has been extensively tested and is now in use at NASA.
Modified Tuned Liquid Column Damper
When waves move a floating wind turbine, they drive fluid motion inside the MTLCD. This forces air in the vertical tanks through an orifice, increasing pressure much like a spring. As the air discharges, the fluid’s motion is damped and energy is dissipated. The MTLCD also incorporates added damping elements, such as an orifice or variable-aperture reciprocating reed valve, that create resistance to air flow, further controlling fluid motion and dissipating energy.
By integrating these modifications, the MTLCD is easily tuned to the platform’s motions, reducing dependency on platform geometry. Eliminating damping elements from the fluid removes the need for marine-grade hardware, reducing system costs. The MTLCD can also be integrated into existing ballast tanks, maximizing space efficiency with minimal added parts.
While initially developed for NASA’s Floating Wind Turbine Development project, this invention can support vibration mitigation applications across multiple industries, such as infrastructure, maritime systems, and aerospace. By enabling precise tuning of dynamic response characteristics, the MTLCD offers a compact solution for platforms requiring vibration suppression. The technology has completed preliminary design and simulation, is at a TRL 3 (proof-of-concept), and is available for patent licensing.
