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July 2012
The Flow
CFD Insights for the Turbomachinery Designer

INSIGHT: A Fireside Chat with Bob Ni
As we celebrate our fourth anniversary, we thought it would be appropriate in this issue of The Flow to take a step back and sit down with Bob Ni to discuss his journey through CFD and some of the philosophical underpinnings behind ADS.  Bob is the Chairman and CTO of ADS.  Prior to founding the company, he was a senior fellow at Pratt & Whitney leading turbomachinery CFD development and application efforts.

FLOW: How did you get your start with CFD?
BOB: I joined Pratt in 1974, and the company really started to invest in CFD in the early 1980s.  it was still in its infancy then and only able to handle simple 2D problems, but it became clear that CFD could serve as a kind of virtual test rig with the potential to reduce redesign, improve safety and contain costs.  
FLOW: From an industry standpoint, what were some of the specific requirements you had for CFD?
BOB:  To get the operational requirements we went to our engine designers.  They told us that it had to be something they could trust, meaning that it had to be independent and not subject to user biases.  It had to provide the highest resolution into problems and deliver valid answers for a variety of geometries it had never encountered.  Ultimately, it had to mimic the physics and do it in design time.
FLOW: That sounds challenging.
BOB: Yes, but we took it in steps and persevered.  Our foundation was a process by which learnings were never lost but always captured to augment our predictive capability. We consistently applied our methodology and never took shortcuts; we knew we wanted a continuous chain of accountability, because that's what building trust meant to us.  And during the course of my 28 year tenure we did in fact develop great confidence in the CFD because that chain of accountability was not broken.  The CFD increasingly became a "system of truth" for exploring uncharted design spaces, so we protected the integrity of the model vigorously.  When data and simulations did not match, we studied all sides of the problem before incorporating the knowledge into our model.  It took years and a lot of sweat, but it's clear that CFD truly helped the company deliver some of the world's most capable turbomachines.  
FLOW: What led you to found ADS?
BOB:  It's a funny story.  I retired from Pratt in 2003 with an intent to play golf, travel and eat lots of sushi, but my side consulting work quickly became a passion.  As part of that consulting I began a search for codes that I felt I could count on for turbomachinery aero, but I just couldn't find something with the appropriate domain expertise and industry bent to make me feel comfortable.  So after a year I took out a clean sheet of paper and started working on a solver an mesher that would let me analyze designs with confidence and stand up to the rigors of modern turbomachinery design.  This led to the founding of ADS.
FLOW: What were some of the key design principles you embraced for your CFD?
BOB:   First, I wanted to craft CFD that turbomachinery clients could use to design with confidence.  I'd learned how to achieve this at Pratt and wanted to impart the best of my experiences into ADS CFD.  Second, I wanted CFD that could address modern turbomachinery design challenges. Third, I wanted to bring these aerospace-class capabilities to the broader turbomachinery market to empower designers at large to be their best.
FLOW: Let's elaborate.  What do you mean by "design with confidence?"  
BOB: "Confidence" is a very subjective word, but to me it means that the CFD consistently discerns design improvements from design mistakes.  CFD that when used correctly, serves as a system of truth for exploring new design spaces.  Confidence also means CFD that's ready for use out of the box, without having to invest years of effort to mature and adapt a generic code to specific needs.  Given my background, I believed I could capture and reflect the learnings I'd accumulated over the years in applying CFD to compressor and turbine design challenges.   
FLOW: What are the "modern turbomachinery design challenges" you allude to?  
BOB: Whether it be a jet engine, a turbocharger or industrial compressor, it's pretty clear that the path to higher performance and efficiency is to reduce size and operate at higher temperatures.  This requires designer insight into the adverse time-varying flow phenomena impacting performance and durability--in other words, time accurate analysis.  I therefore set my sights on delivering a solver that was designed from the ground up for unsteady analysis, and fast enough to be applied inside tight commercial design windows.   
FLOW: How are you making your CFD more accessible to turbomachinery designers?  
BOB: I'm a big believer that turbomachinery aero designers deserve best-in-class, turbomachinery-specific CFD.  We aim to make turbomachinery CFD more accessible by distilling it down to its absolute essence: CFD that has been amply matured in compressor and turbo design, CFD that reduces a myriad of simulation options to the ones that really count, CFD that speaks the language of turbomachinery, and CFD that automates workflows so that designers can focus on design, not on debugging meshes or writing custom scripts.
FLOW: Are there any common pitfalls for companies seeking to take better advantage of CFD for turbomachinery aero?
BOB: The biggest pitfall has less to do with the CFD itself, but rather the analysis methodology by which it is used.  No amount of talent or CFD horsepower can overcome a faulty analysis process.  This problem is becoming more prevalent as CFD expands its reach downmarket to organizations less experienced in its proper application.  Often, the best way for these companies gain their footing is to draw on mentorship from outside experts or CFD vendors like us.   
FLOW: Thanks, Bob.
BOB: My pleasure.
CASE STUDY: Using the ADS Workbench to Analyze the Radiver Centrifugal Compressor  
Centrifugal compressors can be analyzed easily in the ADS Workbench.  In this case study, Michael Ni takes you through the process of setting up the Radiver single stage case in the workbench, generating a speedline and comparing the results to experimental data.   <more>
TECHTIPS: Evaluating Convergence and Conservation with the .STATION file  
The .STATION file produced by Code Leo during a simulation run contains information vital to evaluating the convergence and conservation of a solution.  This guide will teach the user how to read the data contained in the .STATION file as well as describe some of its potential uses.  <more>
Welcome to The Flow

Hello Sir/Madam,

Welcome to The Flow, a newsletter for monthly insights on turbomachinery CFD published by AeroDynamic Solutions, Inc.

Each month we'll spotlight a topic of interest, discuss a case study and/or provide useful pointers about how to get the most out of the ADS CFD system.

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