CFRP Rotor Sleeve Riblets for High-Speed Windage Loss Reduction
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Solution Overview
Problem
Existing rotating electric machines experience windage loss due to turbulent air flow around the rotor, leading to increased friction resistance and reduced energy conversion efficiency, particularly at high rotational speeds, and existing methods for forming fine structures on carbon fiber reinforced polymer sleeves are difficult and prone to cracking.
Innovation Solution
A rotor design featuring a sleeve made of carbon fiber reinforced polymer with a resin film having a ridge structure and riblets formed on its outer circumferential wall, where the resin film is separately processed to create fine ridges and riblets, reducing turbulent vortex generation and maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If fine irregularities are formed on the sleeve made of carbon fiber reinforced polymer, then windage loss is reduced, but it is difficult to form fine structures with high dimensional accuracy and the manufacturing complexity increases
Solution Approach 1:
The invention divides the structure into two separate components: the sleeve made of carbon fiber reinforced polymer and the resin film with fine irregularities. The resin film is formed separately with the desired fine groove patterns, then attached to the sleeve surface. This segmentation allows the fine structure to be created independently on the resin film without requiring complex machining of the sleeve itself, thereby reducing manufacturing complexity while maintaining the windage loss reduction benefit.
Solution Approach 2:
The resin film acts as an intermediary layer between the sleeve and the air flow. Instead of forming fine structures directly on the sleeve, the resin film with pre-formed fine irregularities is attached to the sleeve outer surface. This intermediary approach transfers the fine structure formation process to a more suitable material (resin) that can be easily molded, while the sleeve maintains its structural function.
2Loss of energy
If fine irregularities are formed by machining the sleeve, then windage loss is reduced, but the weight of the armoring increases when using metal materials
Solution Approach 1:
The invention uses a thin resin film with fine irregularities attached to the sleeve surface, replacing the need for thick metal armoring with fine machined grooves. The resin film is lightweight and can be made as a thin layer, significantly reducing the weight compared to metal armoring while still providing the windage loss reduction through its fine groove structure.
Solution Approach 2:
The invention combines carbon fiber reinforced polymer for the sleeve (providing structural strength) with a resin film (providing the fine surface structure). This composite approach allows the lightweight carbon fiber sleeve to maintain structural integrity while the thin resin film provides the aerodynamic benefits, avoiding the need for heavy metal armoring.
3Strength
If a cylindrical body made of metal such as titanium is used as armoring, then rigidity is secured, but it is not easy to form fine irregularities and the weight increases
Solution Approach 1:
The resin film can be easily formed into fine groove patterns through molding processes, unlike metal which requires complex machining. The film is attached to the sleeve surface, providing the desired fine irregularities without the manufacturing difficulties associated with metal forming.
4Loss of energy
If the permanent magnet is heated due to windage loss, then energy conversion efficiency decreases, but forming fine structures on the sleeve is challenging
Solution Approach 1:
By separating the fine structure formation from the sleeve manufacturing, the resin film can be molded with high precision fine groove patterns using standard molding techniques. This achieves the necessary dimensional accuracy for effective windage loss reduction without requiring difficult precision machining of the sleeve.
Solution Approach 2:
The invention changes the material parameter from metal or carbon fiber reinforced polymer (for the fine structure) to resin, which has more favorable molding characteristics. This parameter change enables easier formation of fine structures with high dimensional accuracy through conventional molding processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively reduces windage loss, prevents permanent magnet heating, and enhances energy conversion efficiency by minimizing turbulent friction viscosity and suppressing Taylor vortex generation, while avoiding cracking and weight increase.
Implementation Method 1
When the rotating shaft rotates in this state, an air flow is generated around the rotor. In the case that a rotational speed of the rotating shaft is low, the air flow is laminar. On the other hand, in an aircraft or the like, it is assumed that a rotating shaft is rotated at a high speed. In this case, the air flow becomes turbulent.
Implementation Method 2
Under this condition, the frictional resistance of the rotor to the air layer increases. As a result, so-called windage loss occurs.
Data Source
AI summary
A rotor constituting a rotating electric machine includes a rotating shaft and a permanent magnet. A sleeve covering the outer surface of the permanent magnet is attached to the rotating shaft. The sleeve is made of a carbon fiber reinforced polymer. A resin film is joined to an outer circumferential wall of the sleeve via a joining material. A plurality of ridges are formed on the outer circumferential wall of the resin film. A riblet recessed relatively to the plurality of ridges is formed between the plurality of ridges.