Roger Smith Roger Smith

Sierra Turbines discusses its case study: microturbines

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A new microturbine venture called Sierra Turbines is seeking to revolutionize UAV engines with 3D printing. Using the metal additive manufacturing (AM) technology from manufacturer VELO3D, Sierra Turbines reduced part count in a critical component from 61 to 1 and saw a variety of important performance gains as well.

Sierra Turbines has published a case study on its work with VELO3D. Sierra Turbines CEO Roger Smith also took some time to speak with AUVSI about the case study and the benefits of its microturbine, Aurelius Mk1.

Can you start off by providing our audience with some background information on Sierra Turbines and what you all are seeking to achieve within the UAV industry?

Sierra Turbines was founded in 2017 in San Jose, CA. We are focused on tackling compact, power-dense power generation applications in auxiliary power units (APUs), backup generators and other standby electrical-generation needs.  Another market ripe for innovation is that of propulsion systems for unmanned aerial vehicles (UAVs), both for jet propulsion and hybrid-electric drivetrains.

We had pretty straightforward design objectives from the start, but they are actually very ambitious when compared with existing microturbines: A 40X increase in time-between-overhaul (TBO, which is typically only 25-50 hours for most small turbine engines), significantly increased power-to-weight ratio, and decreased unit cost to machines of comparable power output.

The founding team has gathered multiple decades worth of experience in aerospace, motorsports, and software; with the CEO Roger Smith spending 19 years at Apple before launching Sierra Turbines.

One of the unique things that you all plan to do is additively manufacture (AM) 95 percent or more of your microturbines even when you reach large-scale production, which according to the case study goes against industry belief that AM is limited to prototyping and low-volume work, so how did you come to the conclusion that this method was the best way to go?

Our team has extensive experience with additive manufacturing in the aerospace industry, where the technology has been used extensively for over a decade. For example, each CFM LEAP engine powering the 737 has 19 fuel nozzles that are additively manufactured. By tailoring our designs for additive manufacturing, we can simplify manufacturing, reduce weight and meet our cost target. We believe that embracing AM technology right now with it maturing at its current rate, we will have a steep competitive advantage and that we will reach the economies of scale for our business model very soon.

One of the key pillars of the technology that you all are developing is the metal additive manufacturing system from manufacturer VELO3D; how did your relationship with VELO3D start, and how has that relationship informed your work thus far?

We met VELO3D in 2018 right after the commercial launch of their digital manufacturing solution. Since they are also located in Silicon Valley California, it was easy to visit their headquarters and we were impressed with their team and technology. VELO3D’s applications team has rich knowledge in aerospace like jet engine design; their team brought metal AM to life for Sierra Turbines, and helped us achieve critical design features for our microturbine, while maximizing the benefits of AM. For the gas turbine core, some of the benefits include:

  • Reduced part count. The Aurelius Mk1 core design replaces 61 separate components with one part.

  • Closer tolerances, due to part consolidation, elimination of interfaces, and increased dimensional accuracy.

  • Reduced assembly work and post-processing.

  • Freedom to design complex geometries.

This high level of integration simply wouldn’t have been possible using most currently available AM machines. We approached several of the leading equipment manufacturers and found that none of them could produce the thin-walled, high-aspect-ratio combustor in our Aurelius design. VELO3D certainly has unique capabilities when it comes to manufacturing complex geometries.

The time between overhaul (TBO) for most small turbine engines averages 40 to 50 hours, but you intend to raise that value to 1000+ hours, which is on par with commercial aircraft; what are the benefits of such a large increase, and what will it take to achieve this?

One of our goals is to provide the best solution to power the Federal Aviation Administration (FAA) Part 107 guidelines, which focus on small unmanned aircraft (UAS) operations for drones weighing less than 55 lbs. Here UAVs have hit limits on power density due to lithium batteries storage of just 200 Watt-hours per kilogram. We are offering a 10X increase in power density to 2000 Wh/kg, which enables orders of magnitude of increased flight time and lifting capability. To accomplish this, we needed to address the service interval, and this was in fact what a handful of launch customers are most interested in.

The first part we can talk about today to achieving those lofty goals is the 3D printed engine core in HASTELLOY® X on VELO3D’s Sapphire system. This is the same material that is used in commercial aviation engines from General Electric, Rolls-Royce and Pratt & Whitney. The remaining aspect pertains to turbomachinery and rotating parts, which we cannot disclose details about for now. What we can say is that additive manufacturing allows us to incorporate intricate design features to unlock thermal efficiency and longer servicing intervals previously unseen in this product category.

Where are you all in the development process of your microturbine, Aurelius Mk1?

There is some development remaining as it pertains to the manufacturing and post-processing of the turbomachinery. Our aim is to have a handful of engines running towards the end of 2020.

Once Aurelius Mk1 is complete, how will you all go about commercializing it?

We are in active discussions and have signed agreements with several UAV manufacturers who, pending test data, will be launch customers. Additionally, we intend to work with AUVSI make full use of their expansive network.

How do you all envision your microturbine overhauling the UAV industry?

We see our solution as an enabler to design new UAVs with enhanced capabilities, as well as providing the energy source for UAVs to match and exceed mission profiles of human-operated aircraft. Take, for example, in California where we are located: our utility company uses manned helicopters with LIDAR sensors to inspect 25,000 miles of its infrastructure while flying extremely low at 400 feet. With our powerplant, UAVs can accomplish this mission in a much safer, more expedient manner, more frequently and economically. Our mission is to shift the paradigm in micro-energy solutions.

Sierra Turbines CEO Roger Smith (right) with VELO3D’s Director of Aviation and Power Turbine Solutions, Will Hasting, and several 3D printed engine cores designed by Sierra Turbines and printed with a VELO3D AM machine. The front core is cut open to…

Sierra Turbines CEO Roger Smith (right) with VELO3D’s Director of Aviation and Power Turbine Solutions, Will Hasting, and several 3D printed engine cores designed by Sierra Turbines and printed with a VELO3D AM machine. The front core is cut open to show the intricate internal structure, in which 61 components were combined into one. Photo courtesy of Sierra Turbines.

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Velo3D qualifies Ni-base alloy Hastelloy X for its Sapphire machines

Unicore of a 20-kilowatt microturbine engine, developed by Sierra Turbines, printed on a VELO3D Sapphire metal AM system.

Unicore of a 20-kilowatt microturbine engine, developed by Sierra Turbines, printed on a VELO3D Sapphire metal AM system.

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Velo3D, Campbell, California, USA, has commercially released a production process for additively manufactured parts in Hastelloy® X, a nickel-base alloy suitable for Laser Beam Powder Bed Fusion (PBF-LB) Additive Manufacturing, which is exceptionally resistant to corrosion cracking and oxidation. 

According to Velo3D, Hastelloy X is most often used to manufacture parts for gas turbine engines for combustion zone components due to its high-temperature strength.

“Power generation applications such as industrial gas turbines are a key focus for Velo3D, so it is important that we qualify the right materials to serve that market,” explained Benny Buller, founder and CEO of Velo3D. “We will continue to add more of these types of compatible materials that enable customers to print parts they couldn’t before, yet with even better material properties than those produced by traditional manufacturing.”

Air mobility and power generation provider, Sierra Turbines, San Jose, California, USA, recently partnered with Velo3D to additively manufacture a prototype for its 20 kW microturbine engine with a unicore in Hastelloy X. The company aims to additively manufacture 95% of its engines through metal AM, taking advantage of the design freedom possible through Velo3D’s SupportFree process.

“Sierra Turbines wants to lead aerial and power systems into a new way of manufacturing,” stated Roger Smith, founder and CEO of Sierra Turbines. “That means pushing the limits of what is possible to create a more heat-resistant, lower maintenance, and higher-performing gas microturbine. Velo3D’s technology makes this the ideal manufacturing solution for turbines.”

Velo3D’s patented SupportFree process reduces the consideration of support structures for complex passageways, shallow overhangs and low angles. Coupled with its non-contact recoater, the company states that its AM process can create the intricate cooling passageways and fuel delivery channels needed to achieve high-output fluid transmission and electrical power.

The company recently announced that a 1-meter tall system will be available in Q4 2020, meaning that for what is believed to be the first time, meter-tall parts can be additively manufactured by PBF-LB without support structures, creating new part opportunities for industrial applications. Velo3D’s Sapphire machine is now compatible with titanium 64, Inconel alloy 718, aluminum F357, and Hastelloy X. 

www.velo3d.com

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3D Printed Turbine Combines 61 Parts into One

In July this year, Velo3D had qualified a new nickel-based alloy, Hastelloy X, due to its suitability in the additive manufacturing of power generation components such as gas turbines, using the company’s Sapphire metal AM platform. This announcement had followed relatively quickly on the back of securing the company’s largest order yet, worth $20 million, and raising $40 million in funding which increased the company’s total investment to $150 million till date.

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Industrial gas turbines are a priority application for Velo3D, and offering optimized materials for power generation applications is critical to driving full-scale adoption among its clients. Following the approval of Hastelloy, the company swiftly moved to partner with Sierra Turbines and nTopology, provider of generative design solutions, to test the material in 3D printing 95% of a unicore of a 20-kilowatt microturbine engine. The material is optimized to have high resistance to oxidation or corrosion cracking, resulting in better performing microturbines which require lower maintenance.

The results from the additively manufactured Aurelius Mk1 core really bring home the advantages of using AM over the traditional manufacturing approach. Part count was reduced from 61 separate components to one. This alone eliminates the need to procure and transport various raw materials to manufacture individual parts using different process, as well as the need for assembly of course, involving dissimilar material joints, seals, fasteners. It also reduces post-processing requirements. The reduction of joints, and the ability to design with closer tolerances additionally prevents the possibility of leaks, improving engine efficiency.

AM also allowed designers to build in internal oil and fuel circuits, as well as re-think the fuel spray and flame shape in the combustion chamber. Using the nTop generative design platform, Sierra Turbines modeled a specific lattice geometry to atomize the fuel and a 360-degree fuel injector to distribute fuel equally around the circumference of the combustor. By redesigning from scratch, designers were also able to make the turbine more mass efficient (reducing weight by 50%), resulting in an expected thrust-to-weight ratio (10x increase in power density) significantly higher than existing state-of-the-art turbines of similar power. Regarding the ability to advance design using AM, Roger Smith, CEO of Sierra Turbines, stated,

“My design team is freed from the constraints of traditional manufacturing and even existing metal AM technologies such that they can focus purely on defining the geometry needed to maximize performance and differentiation.”

Image Courtesy of Sierra Turbines

Image Courtesy of Sierra Turbines

This was enabled in no small part by the Velo3D Sapphire Platform, with support-free metal 3D printing, and the new specialized Hastalloy material. The case study from nTopology notes,

“This high level of integration however wouldn’t have been possible using machines other than the VELO3D Sapphire metal 3D printer. The no-contact re-coater blade used in the VELO3D machine allows support-free printing of overhangs down to 30 degrees, which in terms of additive manufacturing freedom is the equivalent of the falling of the Berlin wall.”

Altogether, every one of the benefits AM contributes to increasing the operational time of Aurelius Mk1, with time before overhaul (TBO) 40x greater than existing comparable turbines, and reducing operational cost. This is no small feat, small turbine engines average 40-50 hour between overhaul, and the Aurelius will average a significant 1000+ hours, comparable to that of commercial aircraft. It provides a remarkable demonstration of the difference AM can make in industrial power generation applications, and the results in bringing together specialized AM hardware and software solution providers to develop a revolutionary product.

Image Courtesy of Sierra Turbines

The Aurelius Mk1 will complete development shortly, with a few engines running by end of this year, and commercialization will begin with UAV manufacturers, with whom the company has already signed agreements. The company will to advance optimization and improvement of their Aurelius Mk1 microturbine, stating

Once the combustor has been thoroughly tested and benchmarked, he intends to pursue additional performance improvements. He’s also planning to work on the microturbine’s rotating components, an unorthodox move that many aerospace pundits would agree is beyond the pale. Here again, Smith is determined:

“VELO3D believes that you can use additive for full-scale production, and so do I,” he says. “For future gas turbine development, we aim to leverage the power of additive manufacturing to integrate features such as an efficiency-boosting recuperator, printed-in sensors, and more novel insulating and cooling geometries.”

You can learn more about the development of the Aurelius Mk1 in this webinar, and the full case study can be found here. Earlier this month, Velo3D had also partnered with Lam Research to explore potential applications for its metal 3D printing solutions in the semiconductor industry.

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