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What is blade loading and how is it specified?

Blade loading is the single most important aerodynamic design parameter in turbomachinery blades, it defines both the amount of work made, or extracted, by the blade and the distribution of such work from hub to tip / shroud.

In TURBOdesign1 the design is based on a distribution of swirl velocity or rVθ. In practice the rVθ distribution is not specified directly but through the specification of ∂rVθ/∂m, which directly relates to the pressure loading on the blade. For example, in incompressible potential flow:

Blade Loading | ADT

where:
B : blade number
ρ : density
Wmbl : average of meridional velocity across the blade
r : radius
rVθ : circumferentially mean tangential velocity
m : meridional distance

To fully define the blade loading specification for a given design we follow 3 steps:

  • Impose rVθ spanwise distribution at the INLET section
  • Impose rVθ spanwise distribution at the OUTLET section
  • Impose ∂rVθ/∂m distribution on streamwise sections inside the blade

Step 1: Impose rVθ spanwise distribution at the INLET section

Spanwise distribution of rVθ is specified based on exit swirl distribution from the upstream blade row. In the absence of any blade row zero swirl distribution is specified. 

OUTLET section

 

 

 

 

 

 

 

 

 

Step 2: Impose rVθ spanwise distribution at the OUTLET section 

where:

r : local radius
Vθ: tangential velocity

The exit rVθ is directly related to:

Work input coefficient (rotor): W=ω(r2Vθ2 - r1Vθ1)

Spanwise work distribution (rotor)

Outlet flow conditions (stator)

Spanwise Distribution

 

 

 

 

 

 

 

 

 

Step 3: Impose ∂rVθ/∂m (blade loading) inside the blade

Inside The Blade - Blade Loading

 
 

How do I choose the optimum blade loading distribution?

The optimum blade loading distribution to control given aspects of the 3D flow field has strong generality across designs. The below publications give an introduction to the typical blade loadings used in some common applications. For information related to your specific application, our team is on hand to answer your questions to talk with you about it

  • Secondary flow suppression for centrifugal impellers

Secondary flows are reduced by specifying fore-loading at the shroud and rear-loading at the hub. This type of loading has been found to be applicable to both pumps and centrifugal compressors. Zangeneh et al (1998). 

  • Suppression of corner separation in vaned diffusers

For 3D diffuser design, users typically specify fore-loading at the hub and aft-loading at the shroud. This type of loading helps to remove corner separation in both pump vaned bowl diffusers and centrifugal compressor vaned diffusers. Goto and Zangeneh (1998).

  • Improving pump suction performance whilst maintaining performance

A blade loading distribution in which there is little shroud loading in the first 10% of chord followed by fore-loading results in good suction performance and efficiency. This type of loading has been found to have generality across a wide range of pump sizes and specific speeds.  Bonaiuti et al (2010).

 

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About Advanced Design Technology

We provide software and services for the design and optimization of turbomachinery, based on our unique 3D Inverse Design technology. Our tools and services help customers achieve innovative “breakthrough” designs, delivering market leading solutions at dramatically reduced development costs.

ADT, headquartered in London, UK, was established in 1999 as a joint venture between University College London and The Ebara Research Co Limited of Japan. We are considered as one of the leading global turbomachinery design software providers, with our TURBOdesign Suite tool set in use across a very wide range of applications and sectors. 

Our design consultancy services deliver cutting-edge solutions to our global customers. Whether the task involves a complete solution, from concept to final design for manufacturing, or is facing challenging multi-point / multi-objective design optimization, we work closely with our customers and support them throughout the entire design process.

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