What’s the Difference Between ‘Preliminary’ And ‘Detailed’ Design, And How Do These Design Phases Fit Into Your Turbomachinery Design Project? (2023)

Whether it’s a compressor, turbine, or an entire rocket turbopump design project we are tackling at Concepts NREC, we typically divide the design project into three phases: (1) scoping or feasibility study, (2) preliminary design, and (3) detailed design. Each of these phases has a specific purpose, although where one phase ends and the next phase begins can vary from project to project. The purpose and need for a scoping study was described in my blog posted last month, Why are Scoping Studies Necessary for Your Turbomachinery Project? In this blog I will describe the difference between preliminary design and detailed design.

Let’s start with summarizing what is accomplished during a scoping study phase. In this phase, initial calculations are performed to ‘size’ the piece of turbomachinery to meet what are often preliminary design specifications. This sizing includes determining the type and configuration of the turbomachinery (axial or radial, single stage or multistage), as well as operating characteristics (optimal rotational speed, performance maps). For a more complete scoping study, a preliminary 2D layout is created that reflects mechanical aspects of the design (bearing type and placement, seal type, housing layout, etc.). Often several configurations will be considered, and the best configuration with respect to the parameters most important to the client (performance, simplicity, design cost, manufacturing cost, etc.) will be selected for further design effort.

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With these initial calculations complete, the next level of design work can begin, but only after one other item is available: a complete design specification. If a design specification was not completed as part of the scoping study, the specification must be completed before further design work can begin. The client can complete the design spec themselves, or we can help the client ‘fill in the blanks’ and define a complete spec. More times than we would like to admit we have started a design and realized that the design intent was in some way not fully defined or not fully understood by either us or our client, hence we are very particular about having a complete design spec in place. More detailed design specs are needed for a preliminary/detailed design than for a scoping study. For example, often in a scoping study only a single design point is considered. If there are multiple off-design points that are important to the client, these off-design points should be considered during the scoping study, or at least fully identified in a design spec so they can be addressed during preliminary/detailed design. Often in scoping studies the focus is on aerodynamic performance to see if a cycle condition can be met, an outcome which might determine if a project is viable. But in preliminary/detail design, mechanical design often dominates the effort and all specifications related to mechanical design must be in place, including items like life requirements (number of cycles, number of operating hours), environmental considerations (this unit must run in -30F to +120F ambient conditions), manufacturing limitations (we don’t want to pay for expensive/exotic materials), and interface requirements (how will the unit be mounted? what types of fittings are needed for instrumentation leads? etc.). Indeed, an entire blog could be written just on how important it is to have a full design specification in place before preliminary/detailed design begins.

After the scoping study is complete and a good design spec is in place, further design work can begin. This design work is typically divided into at least two phases, preliminary design and detailed design. with each of these phases having a different purpose as follows.

What’s the Difference Between ‘Preliminary’ And ‘Detailed’ Design, And How Do These Design Phases Fit Into Your Turbomachinery Design Project? (1)

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Preliminary Design

In the preliminary design phase, more detailed engineering design/analysis calculations are performed on at least the major elements of the component. The major elements include the aerodynamic flowpath (inlets, impellers, diffusers, exit elements), the rotating group (shafting, bearings, seals), and the static housings (including the bearing housing). A first pass analysis is typically done in each technical area in order to further develop the design. In addition, relative to a scoping study, in a preliminary design the next level of sub-component detail is examined. This next level can include looking at parameters such as seal leakage, axial and radial thrust (and thrust control if thrust exceeds bearing capacity), mechanical containment, impeller/rotor attachment, etc.

One of the hallmarks of the preliminary design phase is the execution of trade studies. Typically in turbomachinery design there are options on how you can approach a design or analysis, and a trade study is often used to determine the best path forward. A trade study could involve selecting the best rotational speed to optimize the overall performance of a turbopump, where the optimal speed for the pump and for the turbine are different. Or a compressor might operate over a range of conditions (high flow/high pressure ratio, low flow/high pressure ratio, low flow/low pressure ratio), and the best ‘design point’ is not really at any of these three conditions (https://www.conceptsnrec.com/blog/there-is-no-such-thing-as-a-design-point), and a trade study or optimization might have to be done to select the best design point. Trade studies are often done for mechanical components, perhaps evaluating several different bearing types to select the most suitable bearing given rotordynamic, life, and cost requirements. Trade studies and trade tables are common in the preliminary design phase as the design is refined from a concept to more of an optimized configuration. For these trade studies our clients often identify the drivers and priorities for their project, including factors such as aerodynamic performance, operating life, size/weight, manufacturing cost, development time/cost, etc., so we know how to weight the trade studies.

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How do you know when a preliminary design is complete? At the end of preliminary design, it is typical that a layout has been solidified, subcomponents have been down-selected (bearings, seals, etc.), a first pass analysis of at least all critical components has been completed, and a refined performance estimate has been generated. Note that the design is not final and not all needed analyses have been completed, but enough work has been done to verify the design is viable and is still capability of meeting the design specification. Another important outcome from preliminary design is the identification of risk areas that must be further addressed in detailed design, typically by refined and more involved analysis. To be honest it can be somewhat gray when a preliminary design is complete and the detailed design can start – usually we work out this split with our clients during the proposal/planning phase of a project. One last critical element of the preliminary design phase is a complete design review, always internally, and often externally with our client if they chose to be involved at this level to fully review the work done to date and to agree to proceed with detailed design.

Detailed Design

In the detail design phase, analyses are taken to the next level, either refined to be more accurate, or extended to additional operating conditions. There is a saying that goes ‘the devil is in the details’, sometimes attributed to the German philosopher Nietzsche. While Nietzsche might have intended a more philosophic meaning, we can certainly apply this saying to the design phase of turbomachinery. There are typically a lot of details in detailed design that need to be analyzed, refined, and completed correctly for the turbomachinery component to fully vetted and optimized. Even when an analysis is refined and run with perhaps a higher density mesh or more refined boundary conditions, the analysis is still often not done, and must be re-run at other operating conditions or other ambient conditions. The detailed design phase is where all this refinement happens, and this phase of the project can be the most cost and schedule intensive phase.

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At Concepts NREC, we usually include the creation of CAD models and manufacturing drawings in the detailed design phase. Sometimes the CAD work is broken out separately depending on the needs of our clients, but often CAD models are made anyway during the detailed design phase for either component analysis or to complete a layout/assembly, so it makes some sense to keep the detailing of the models for manufacturing and the creating of the associated manufacturing drawings in the detailed design phase. Indeed, tasks like tolerances stacks to set drawing/manufacturing tolerances are best done in conjunction with the analyses that give input to these stacks (such as calculation of hot-to-cold deflections). In many cases the end of the detailed design phase is indicated by completion of manufacturing drawings. Certainly, detailed design reviews must also be held to close out the design effort, but many consider best practice to have reviews before the manufacturing drawings are completed or even started, in order to catch any issues in time for a last round of design/analysis refinement.

What’s the Difference Between ‘Preliminary’ And ‘Detailed’ Design, And How Do These Design Phases Fit Into Your Turbomachinery Design Project? (2)


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The information presented here is just a brief overview of these two design phases; there is so much more to organizing and running a project. At Concepts NREC we follow many of the Project Management Institute (PMI) guidelines, and many of our staff are PMI trained. Topics such as risk management, concurrent engineering (including ordering long lead time parts before design is complete), and resource availability and loading should be all addressed in any project plan, no matter how you break up your design phases. In addition to applying PMI principles for project management, Concepts NREC is ISO9001 and AS9100 certified, and we follow procedures defined for these quality management systems in our project planning and execution.

If you would like to discuss how we would approach your turbomachinery design project, please contact us at info@conceptsnrec.com #turbomachinery #engineering#compressor #turbine #pump


What is the difference between preliminary design and detailed design? ›

During detailed design and optimization, the parameters of the part being created will change, but the preliminary design focuses on creating the general framework to build the project on.

What are the two design phases for the preliminary and final design? ›

This design work is typically divided into at least two phases, preliminary design and detailed design. with each of these phases having a different purpose as follows. In the preliminary design phase, more detailed engineering design/analysis calculations are performed on at least the major elements of the component.

What is a detailed design phase? ›

Detailed design is the phase where the design is refined and plans, specifications and estimates are created. Detailed design will include outputs such as 2D and 3D models, P & ID's, cost build up estimates, procurement plans etc. This phase is where the full cost of the project is identified.

What is preliminary design phase? ›

Preliminary design is the stage in which general project location and design concepts are determined. It includes all that is necessary to conduct a NEPA alternatives analysis and review process properly, but good preliminary design goes beyond that.

What is PDR and DDR? ›

3. DDR - Detail Design Review. 4. PDR - Prototype Design Review.

What does PDR mean in project management? ›

The Preliminary Design Review (PDR) closes the preliminary design phase of the project.

What does detailed design include? ›

Detailed design includes outputs such as 2D and 3D models, plans, detailed and assembly drawings, Bill of Materials, cost estimates, procurement plans etc. Here you identify the full cost of the project.

What are the 3 phases of the design process? ›

The Three Phases of Design Thinking: Immersion, Ideation and Prototyping. The Design Thinking approach have changed the way thousands of companies think (and do) innovation. Start your transformation from 3 basic standards: Immersion, Ideation and Prototyping.

What are the different phases of design? ›

The Five Phases of Design Thinking

The short form of the design thinking process can be articulated in five steps or phases: empathize, define, ideate, prototype and test. Let's briefly explore each of these phases in relation to a practical design process.

What is the purpose of detailed design? ›

The goal of the detailed design stage is to develop the sketch design into working drawings and specifications suitable for construction purposes. During this stage the cost consultant will be expected to review the project and cost plan on a regular basis and provide advice if the cost appears to be increasing.

Why is it important to use detailed drawing in making a design or project? ›

Drawings are important because they are used to communicate the technical details of a project in a common format. The drawings also become the foundation for future projects and cost savings for customers.

What is the most important phase in the design process? ›

Research is the most important part of any Design process. The facts and insights you acquire during the Research phase inform every subsequent part of the design process. More importantly, it is during research that you can easily kill ideas.

What is the design phase of a project? ›

Project design is an early phase of the project lifecycle where ideas, processes, resources, and deliverables are planned out. A project design comes before a project plan as it's a broad overview whereas a project plan includes more detailed information.

How do you create a preliminary design? ›

4 Tips for Better Preliminary Design
  1. Start at the end. You won't get anywhere without first determining the purpose and need for your project and then developing a clear vision for success. ...
  2. Give yourself options, but not too many. ...
  3. Save a seat at the table for the community. ...
  4. Be flexible, but firm.

What is preliminary design in project report? ›

The Preliminary Design Review (PDR) is a technical assessment that establishes the Allocated Baseline of a system to ensure a system is operationally effective.

What should a preliminary design review include? ›

Preliminary Design Review (PDR)

Ensure that all system requirements have been validated, allocated, the requirements are complete, and the flowdown is adequate to verify system performance. Show that the proposed design is expected to meet the functional and performance requirements.

What is a detailed design review? ›

Detailed Design Review means the process that focuses on the System level components and individual Site-specific characteristics and establishes the Site-specific Statement of Work for each Region.

What are the main phases of a design review? ›

Design Review Agenda Template

Design Review: Designers and product managers share the design while participants take notes. Feedback Review: Participants share feedback. Prioritization: The designer and product managers discuss the next steps/decisions with decision-makers.

What does PDR stand for in development? ›

Purchase of development rights (PDR) is a tool that provides a way to financially compensate willing landowners to protect the natural heritage of their land versus undertaking a development project.

How do you conduct a PDR? ›

7 Tips on How to Conduct a Meaningful Personal Development Review
  1. Set your stall out. First of all, you, as a manager, must buy into the PDRs yourself. ...
  2. Clear your diary. ...
  3. A two way street. ...
  4. No alarms and no surprises. ...
  5. Silence is golden. ...
  6. A review of the year. ...
  7. No fudging.

What should a detailed design document contain? ›

To start, the following is a list of sections that you should at least consider including in your next design doc:
  • Title and People. ...
  • Overview. ...
  • Context. ...
  • Goals and Non-Goals. ...
  • Milestones. ...
  • Existing Solution. ...
  • Proposed Solution. ...
  • Alternative Solutions.
13 Jul 2018

What is a detailed design specification? ›

The Detailed Design Specification (DDS) describes how the hardware and software functionality identified in the Functional Specification will be developed and implemented. The Hardware DDS is a description of the hardware on which the software resides and how it is to be connected to any existing system or equipment.

What is the purpose of the design phase? ›

The purpose of the Design Phase is to transform the requirements into complete and detailed system design specifications. Once the design is approved, the Development Team begins the Development Phase.

What is the three phase design model? ›

The 3P RPID Model is a general model that allows for a great deal of flexibility when dealing with a range of solutions over a variety of contexts. Three Phases This ID Model is marked by three developmental phases: Front-End Analysis, Rapid Prototyping (design and development), and Project Deployment.

What are the 7 phases of design plans? ›

Seven Stages of Design Thinking; An Essential Tool for Customer Experience Manager
  • Stage 1: Understand the Customer. ...
  • Stage 2: Definition. ...
  • Stage 3: Research. ...
  • Stage 4: Ideation. ...
  • Stage 5: Prototype. ...
  • Stage 6: Select and Implement. ...
  • Stage 7: Learn.
29 Apr 2016

Why are detailed drawings important? ›

Specifications will detail the materials, principles, procedures, etc needed to complete the works. Construction drawings give the graphical portrayal, indicating the course of action of parts, detailing, measurements, etc.

What are the two purpose of detailed drawing? ›

A detail drawing provides complete and precise descriptions of a part's dimensions, shape and how it is manufactured. A detail drawing should be concise, in that it conveys only the information needed to create the part.

What are the characteristics of a detailed working drawing? ›

The Detail Drawing

It will be clearly labeled with a part number and name, It may include several views of the object--top, front and side--and a projection view. These drawings are annotated with information, including overall and detail dimensions, tolerances, materials, and treatments.

What are the features required for detailed building drawing? ›

This drawing contains details like Index Plan, the cross-section of walls, detailed plan, elevation, cross-section, floor, and roof, etc. It also contains the detail of sizes of doors, windows, specifications, and other constructional detail.

What are the main phases in design and development? ›

The 5 phases of a design project are Schematic Design, Design Development, Construction Documents, Bidding, and Construction Administration, according to the American Institute of Architects (AIA).

What are the key elements of design phase? ›

The elements of design are the fundamental aspects of any visual design which include shape, color, space, form, line, value, and texture.

What are the 5 phases of a project with examples? ›

The project management life cycle has five main phases. These are project initiation, project planning, project execution, project monitoring and control and project closure. Each of these stages will be examined in turn.

What are the 4 main project phases and what do we do? ›

Planning, build-up, implementation, and closeout.
Determine scope, resources, and major tasks.
  • Ask, “What will have to be done in order to accomplish X?”
  • Continue to ask this question until your answer is broken down into tasks that cannot be subdivided further.
3 Nov 2016

What is preliminary process? ›

Definition. Any introductory action in the judicial process designed to determine the need for further court involvement or to expedite a motion that requires immediate attention.

What is the purpose of preliminary drawings? ›

A drawing (sketch) or a plastic model, made to study, design or give an idea of the appearance of an object, or of its functioning.

What is preliminary product design? ›

By preliminary production design I mean to design the product with just enough detail to answer some important questions. But without worrying yet about the tiny details that don't have a big impact. The problem is that once you dig into the full design you tend to get buried in the technical details.

What sections are there in a preliminary design? ›

The key elements of most preliminary designs include an outline of the following items: the design's systems, its basic requirements, and the high-level design features.

What is difference between process design and detailed equipment design? ›

The design starts at a conceptual level and ultimately ends in the form of fabrication and construction plans. Process design is distinct from equipment design, which is closer in spirit to the design of unit operations. Processes often include many unit operations.

What is a detailed design drawing? ›

A "detail drawing" is a drawing of a single component, assembly of multiple parts, or an entire system of assemblies. A detail drawing provides complete and precise descriptions of a part's dimensions, shape and how it is manufactured.

What is the difference between architectural design and detail design? ›

Architecture design is more abstract than detailed design and it specifies the fundamental structure and patterns of the system under development. Detailed design focuses on all of the implementation details necessary to implement the architecture that is specified.

What is the difference between FEED and detailed design? ›

Detailed Engineering is the design phase when all design work in done in detail to put into construction and operation. FEED is done mainly to assess the cost and produce preliminary basis documents. Detailed Engineering is the design phase when all design work is done in detail to put into construction and operation.

What is detail design in product design? ›

The detail design phase involves completing the product's design. The design team works toward completion of the specifications for the product and its subassemblies, product elements, and manufacturing processes. Like the other phases of product development, detail design is an iterative process.

What are the two types of design processes? ›

3 key types of process design
  • Process mapping. Process mapping is a catch-all design process that can be used in virtually any business scenario. ...
  • Serial vs Parallel process design. ...
  • Process improvement.
23 Jun 2020

What is system design and detailed design? ›

Thus, the main objective of the detailed system design is to prepare a blue print of a system that meets the goals of the conceptual system design requirements. Detailed system design involves the following phases. Project planning and control. Involve the user. Define the detailed sub-system.

What do you mean by architectural and detailed design? ›

Detail Design (DD) in architecture is the sum of drawings concerning the construction details, the characteristics of the materials and the construction methods of the project. It is an integral part of the Architectural Study, while its purpose is to cover every construction aspect of the project, until its delivery.

Why is architectural detailing important? ›

In the short term, good detailing can lead to a smoother construction process. Thinking through the smallest elements in a space ensures that contractors are prepared for the work that goes into the build itself. There are fewer miscommunications and shortcomings when every step is accounted for in the plans.

What is detail architecture? ›

Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing buildings or other structures.

What is the difference between FEED and EPC? ›

FEED (Front End Engineering Design) means Basic Engineering which is conducted after completion of Conceptual Design or Feasibility Study. At this stage, before start of EPC (Engineering, Procurement and Construction), various studies take place to figure out technical issues and estimate rough investment cost.

What is feed project phase? ›

During the FEED phase, there is close communication between Project Owners and Operators and the Engineering Contractor to work up the project-specific requirements. Front-End Engineering focuses on technical requirements and identifying main costs for a proposed project.

What is feed and pre feed? ›

Pre-FEED is a preliminary FEED (front end engineering and design) document that is a predefined design package to prove the feasibility in technical and economics. The Pre-FEED is used to a basis of FEED deliverables or basic engineering. ( Refer to the FEED (Front End Engineering and Design))


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