Impeller Tip Leakage Sealing and Flow Straightening in Compressors
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Solution Overview
Problem
Compressor performance is reduced due to tip leakage and unwanted noise caused by air flowing back through the clearance between the stationary housing and rotating blade tips, leading to pressure losses and swirl-induced inefficiencies.
Innovation Solution
A compressor design incorporating a labyrinth seal arrangement and a flow straightening arrangement to minimize tip leakage and swirl, featuring interdigitated shroud and housing rings forming a tortuous path, and a wake recovery chamber to homogenize airflow before reinjection into the impeller.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If air is drawn through the impeller at high flow rates, then compressor throughput is improved, but tip leakage increases causing pressure losses and reduced efficiency
Solution Approach 1:
A labyrinth seal arrangement is introduced as an intermediary structure between the impeller and housing. This seal consists of alternating stationary and rotating lobes that create a tortuous flow path, forcing leakage air to reverse direction multiple times. The labyrinth seal mediates the clearance gap, reducing the effectiveness of the leakage path while maintaining the necessary clearance for impeller rotation, thereby reducing pressure losses without compromising throughput.
Solution Approach 2:
The leakage flow path is extended from a simple radial clearance into a three-dimensional tortuous path through the labyrinth seal. By adding axial and circumferential components to the flow path that would otherwise be purely radial, the seal increases the effective length of the leakage path and introduces flow reversal, thereby reducing leakage losses while allowing high throughput operation.
2Ease of operation
If tip leakage is allowed to occur, then clearance for impeller rotation is maintained, but noise is generated from swirling air reinjection at the inlet
Solution Approach 1:
The labyrinth seal acts as an intermediary that modifies the characteristics of leakage air before it reaches the impeller inlet. By forcing the air through a tortuous path with multiple direction changes, the seal dissipates the rotational momentum and swirl of the leakage air, transforming it into a more uniform flow that reinjects gently into the inlet without generating noise.
Solution Approach 2:
The leakage air that would otherwise be harmful (swirling, noisy, energy-wasting) is converted into a beneficial pre-swirled flow that can be smoothly integrated into the inlet flow. The labyrinth seal transforms the harmful high-velocity swirl into a controlled, low-velocity flow pattern that actually helps homogenize the inlet conditions without generating noise.
3Device complexity
If a simple clearance path is used between shroud and housing, then device complexity is reduced, but tip leakage and associated performance losses increase
Solution Approach 1:
The clearance path is segmented into multiple sections by dividing the labyrinth seal into alternating stationary and rotating lobes. This segmentation creates multiple flow reversals and direction changes within the same radial clearance space, effectively reducing tip leakage without requiring additional axial space or complex external structures. The segmented design achieves high performance while maintaining simplicity.
4Quantity of substance
If swirl is induced in leakage air by boundary layer friction on the shroud, then air flows through the leakage path, but efficiency is reduced and additional noise is created upon reinjection
Solution Approach 1:
The labyrinth seal introduces periodic direction changes to the leakage air flow as it passes through the alternating lobes. This periodic action of forcing the air to reverse direction multiple times dissipates the continuous swirl that would otherwise be generated by boundary layer friction, converting the steady rotational motion into a series of controlled, small-scale flow reversals that reduce overall swirl and improve efficiency.
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 significantly reduces tip leakage and associated noise, enhancing compressor efficiency and performance by minimizing pressure losses and swirl-induced inefficiencies.
Implementation Method 1
The labyrinth seal arrangement of the compressor is advantageous as it provides a tortuous flow path between the shroud and the housing of the compressor, so as to reduce the rate of air flow from the impeller outlet back towards the impeller inlet through the leakage flow path.
Implementation Method 2
This air is already swirling on exit from the impeller, and further swirl is induced by boundary layer friction as the air passes the front surface of the shroud as it flows through the tip leakage path.
Implementation Method 3
Furthermore, for air that does flow through the leakage flow path, swirl in the flow that is generated by boundary layer friction on the outer surface of the rotating shroud is removed or at least reduced by the flow straightening arrangement.
Implementation Method 4
This chamber advantageously acts to homogenise the tonal content of the air flow exiting the flow straightening arrangement, and allows the aerodynamic wakes that may be created on flow of air through the flow straightening arrangement to mix out before interacting with the impeller blades on reinjection into the impeller.
Data Source
AI summary
A compressor is provided for use in domestic appliances. The compressor includes: an impeller including an inlet, an outlet, a hub defining a rotational axis of the impeller, a plurality of impeller blades that extend from the hub, and a shroud that at least partially surrounds the impeller blades; a housing that at least partially surrounds the shroud and that is coaxially arranged with respect to the rotational axis of the impeller to allow the impeller to rotate within the housing; a leakage flow path defined between the shroud and the housing leading from a leakage flow path inlet to a leakage flow path outlet; a labyrinth seal arrangement provided in the leakage flow path; and a flow straightening arrangement having an inlet at an outlet of the labyrinth seal arrangement.