Wind Tunnel Nozzle Jet Guide Element Resonance Control
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Solution Overview
Problem
Wind tunnels with closed air ducts and free jet measuring sections experience low-frequency pressure oscillations due to resonance phenomena, which can affect acoustic and aerodynamic measurements, and existing solutions like Seiferth vanes generate noise and alter the static pressure profile.
Innovation Solution
The implementation of jet guide elements on the inner nozzle wall of the wind tunnel nozzle, which extend in the flow direction and have a width transverse to it, helps to break up coherent vortex structures by generating longitudinal vortices that interact and destroy ring vortices at the nozzle outlet, minimizing resonance excitation without additional noise or structural changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Seiferth vanes are arranged downstream of the nozzle outlet edge to break up vortex structures, then resonance excitation is prevented, but strong inherent noise is generated and static pressure profile is altered
Solution Approach 1:
The jet guide element is positioned upstream of the nozzle outlet edge to generate longitudinal vortices before the flow exits the nozzle. This preliminary action disrupts the formation of coherent ring vortices at the outlet, preventing resonance excitation without requiring downstream interventions that would generate noise.
Solution Approach 2:
The jet guide element acts as an intermediary structure that introduces longitudinal vortices as a mediating flow feature. These longitudinal vortices interact with and destroy the ring vortices formed at the nozzle outlet, thereby preventing resonance while avoiding the direct contact with the free jet that would cause noise generation.
2Reliability
If Seiferth vanes are used to break up vortex structures, then resonance is prevented, but the static pressure profile in the free jet is influenced
Solution Approach 1:
By positioning the jet guide element upstream of the nozzle outlet edge, the longitudinal vortices are generated in advance to disrupt ring vortex formation. This preliminary disruption occurs in a controlled region where it does not directly interfere with the free jet's pressure development, thus preserving the static pressure profile while still preventing resonance.
3Measurement precision
If complex noise cancellation systems are implemented to address resonance, then acoustic measurements can be improved, but device complexity increases
Solution Approach 1:
The jet guide element converts the potentially harmful coherent vortex structures into beneficial longitudinal vortices that naturally disrupt the ring vortex formation. This passive flow control mechanism improves acoustic measurement conditions by eliminating resonance without requiring complex active noise cancellation systems.
4Measurement precision
If structural interventions are made in the wind tunnel to eliminate resonance, then measurement accuracy improves, but manufacturing complexity and cost increase
Solution Approach 1:
The jet guide element is designed as a separate, modular component that can be independently manufactured and installed in the nozzle. This segmentation allows for easy manufacturing and installation without requiring complex modifications to the overall wind tunnel structure, thus improving measurement accuracy while maintaining ease of manufacture.
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
This solution effectively prevents resonance excitation in the plenum and air duct, stabilizes the free jet, and improves acoustic conditions in wind tunnels, allowing for accurate aeroacoustic measurements without the need for complex noise cancellation systems or structural interventions.
Implementation Method 1
Longitudinal vortices with an axis of rotation parallel to the direction of flow roll up on the longitudinal edges as a result of pressure differences occurring between areas with jet guide elements and areas without jet guide elements
Implementation Method 2
pressure differences occurring between areas with jet guide elements and areas without jet guide elements on the inner nozzle wall
Implementation Method 3
effectively prevent the excitation mechanism for resonance formation with little design effort, without major structural interventions in the wind tunnel
Data Source
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AI summary
The wind tunnel nozzle (14) has an inner nozzle wall, a nozzle outlet edge and a device for breaking the coherent vortex structures of a free jet (16) released from the wind tunnel nozzle. The device has a jet guiding element, which is arranged at the inner nozzle wall and extends in a flow direction. The jet guiding element has a guide surface, which points away and protrudes from the nozzle wall. The jet guiding element defines a longitudinal direction, which extends parallel to the flow direction. An independent claim is included for a wind tunnel with a collector.