Software for Fluid Power Technology

From Editor

The purpose of the Software Review section of the Journal is to present information to the reader about engineering software, including simulation programs, to highlight their specific features and their "fitness to purpose" in the unique field of fluid power and motion control. It is, of course, impossible to establish evaluation criteria matching the needs of all readers, therefore readers should not look for absolute ratings but more or less "fuzzy" opinions of the reviewer. A software program is like a wrench, just a tool to solve problems. It is good to solve some problems and not so good for others and this depends on both the nature of the problem and the users' attitude - and generally when we review software we do not know either. A software tool can be highly specialised and great for a some applications but not so well suited for others, on the other hand another software tool can be more flexible and generally applicable but without outstanding features. It is impossible, and even misleading, to say which one is better. What we hope to accomplish is to give the reader information necessary to take his/her own decision.

Modelling and Simulation of Pump Designs
with CFdesign®


1 Introduction

History    Since 1992, the Blue Ridge Numerics mission has been to deliver a fluid flow and heat transfer simulation that is both affordable and practical for mainstream product development groups.
Blue Ridge Numerics is well established in Asia, Europe and North America and CFdesign is considered by most industry observers to be the new Upfront CFD standard for fluid flow and heat transfer simulation where fluid and thermal analysis simultaneously joins the design process as CAD models are developed.
With high-level developers from the nuclear and fossil fuel divisions of Babcock & Wilcox and other major industrial and computational simulation companies, Blue Ridge Numerics has decades of experience in the rotating machinery and pump industries.

2 CFdesign

   Throughout the history of pump design, there has always been a significant effort dedicated to improving pump efficiency, increasing duty cycle, and broadening operating range. Engineers have been faced with the task of creating multiple castings for housings, impellers, and other machine components only to find that they could be made better after-the-fact. More prototypes were made until the budget of the project required a final prototype to go into production.
From the beginning, CFdesign was developed to exist as a tool on the desktop of engineers tasked with the creation of new pump designs.
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Fig. 1: CAD model of proposed pump design






   Because almost all new pump designs start with a complex CAD model, CFdesign also starts with the pump CAD model and provides insight into the details of the flow, performance, and motion characteristics of the machine. While this tool is not meant to replace the final prototype, it can significantly reduce the engineering time spent iterating towards the optimal design of the new pump.
The process for designing a new pump in CFdesign begins in the engineer’s native CAD system as shown in Fig. 1.
This design is immediately taken into CFdesign and the appropriate flow conditions are specified. Conditions such as backpressure, head, temperature, rampedin pressures / flow rates, and more, are applied directly on the CAD model, as shown in Fig. 2.
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Fig. 2:Application of flow conditions on CAD model



   While this is a centrifugal pump example, many times the pump design in question has much more complex motion characteristics such as intermeshing parts (screw compressors, gear pumps, etc). These motion definitions are easily defined in CFdesign. Fig. 3 shows some of the options available to engineers designing such devices.
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Fig. 3:Flow-driving or flow-driven motion application for any type of motion



After applying conditions the engineer is familiar with for this particular pump and the type of motion the pump will be experiencing, CFdesign solves the entire machine for the motion and structure interaction (field variables include, pressure, absolute velocity, relative velocity, turbulence levels, and temperatures) of the fluid medium moving through the machine. See Fig. 4 for an example of a live solution window from this tool.
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Fig. 4:A live view into the details of fluid flow through the proposed pump design



Insight gained in this single analysis is comprehensive using tools like virtual probe plotting (see Fig. 5), fluid particle trace simulation (see Fig. 6), and sectional views showing impingement and downstream separation following the cutwater (see Fig. 7).
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Fig. 5:Virtual probe plotting anywhere inside the machine to show any result



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Fig. 6:Fluid particle (or massed particle) simulation showing flow or areas of stagnation / erosion



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Fig. 7:Cross-section view showing flow vectors and excessive separation at cutwater



Based on insight gained from CFdesign, pump engineers typically modify the initial CAD design and run 3 to 20 or more different virtual prototypes quickly.
These are then compared side-by-side on a single screen to find the optimal design.


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Fig. 8:CFdesign full-spectrum flow curves for a single and
double volute design compared side by side for target operating conditions



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Fig. 9:CFdesign efficiency based on native CAD designs
compared run with target head rise and actual working fluids



From the CFdesign analysis, a full range of pump curves and wall force calculations are extracted from the results automatically (see Fig. 8, 9, and 10).
The use of CFdesign accelerates to the point where fully defined pump curves are already in the engineer’s hand and only need be verified typically with one physical prototype.


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Fig. 10:CFdesign automatic wall calculator report for
impeller balancing and side load prediction based on single and double volute designs



5 Summary

   From the engineer’s perspective CFdesign is simply part of the design process for designing new rotating machinery. From the initial concept of a new pump design, CFdesign is incorporated in the upfront design process to guide the design decisions toward the optimal solution. Our customers report saving hundreds of thousands of dollars on prototype production and months of research and development time.
When the invisible fluid interaction inside a complex turbo-machine becomes visible to the engineer immediately on the CAD model concept, a tremendous leap of insight saves the design process from hidden errors inside the machine. Predicting and avoiding impingement and erosion before it destroys a physical model, visualizing the pump performance immediately before spending months waiting for the flow bench results to complete, and reaching the optimal design with the confidence, it will perform to specifications on the first prototype run, are all things CFdesign users enjoy.


 

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