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DE-102024210813-A1 - Helmholtz resonator

DE102024210813A1DE 102024210813 A1DE102024210813 A1DE 102024210813A1DE-102024210813-A1

Abstract

A Helmholtz resonator with an adjustable resonant frequency is proposed. Individual side walls or sections of side walls of the resonator neck are variable in length or area, separating the interior from the exterior. For example, window-like, closable openings can be provided in the side walls. These openings can be arranged offset from one another longitudinally to achieve a wider range of adjustable resonant frequencies.

Inventors

  • Marcus Casper
  • Leon Döring
  • Martin Prätz

Assignees

  • VOLKSWAGEN AKTIENGESELLSCHAFT

Dates

Publication Date
20260513
Application Date
20241111

Claims (10)

  1. Helmholtz resonator (4) with a resonator volume (6) and with a resonator neck (10) having a plurality of side walls (12, 18, 24, 26), wherein the resonator neck (10) is designed such that the size of at least one surface of a side wall (12, 18, 24, 26) of the resonator neck (10) bounding a volume of the resonator neck (10) can be varied independently of the sizes of the surfaces of the other side walls (12, 18, 24, 26).
  2. Helmholtz resonator (4) according to Claim 1 , wherein the resonator neck (10) is arranged within the resonator volume (6).
  3. Helmholtz resonator (4) according to one of the preceding claims, wherein at least one of the side walls (12, 18, 24, 26) of the resonator neck (10) has at least one closable opening (14, 16, 20, 22) for varying the size of the surface of the side wall (12, 18, 24, 26) of the resonator neck (10).
  4. Helmholtz resonator (4) according to one of the preceding claims, wherein a plurality of side walls (12, 18, 24, 26) of the resonator neck (10) each have a plurality of closable openings (14, 16, 20, 22).
  5. Helmholtz resonator (4) according to Claim 4 , wherein a first row of openings (14, 16) in a first side wall (12) of the resonator neck are arranged offset along a longitudinal axis of the Helmholtz resonator (4) from a second row of openings (20, 22) in a second side wall (18) of the resonator neck.
  6. Helmholtz resonator (4) according to one of the preceding claims, wherein the resonator neck (10) has at least one opening (14) that can be closed with a cover (42) for varying the size of the surface of the side wall (12, 18, 24, 26) of the resonator neck (10).
  7. Helmholtz resonator (4) according to one of the preceding claims, wherein at least one side wall (12, 18, 24, 26) has an open area in which sliding closure elements (50, 52) are arranged along a longitudinal axis of the Helmholtz resonator.
  8. Helmholtz resonator (4) according to Claim 7 , wherein several of the locking elements (50, 52) are designed to be connectable and separable from one another.
  9. Helmholtz resonator (4) according to one of the preceding claims, wherein at least one of the closure elements (50) is connected to a drive for displacing the closure element (50) along the longitudinal direction of the Helmholtz resonator (4).
  10. Wind tunnel (2) with a Helmholtz resonator (4) according to one of the preceding claims.

Description

The invention relates to a Helmholtz resonator with a resonator volume and with a resonator neck having a plurality of side walls, as well as a wind tunnel. A Helmholtz resonator essentially consists of a cavity, usually referred to as the resonator volume, and a relatively smaller neck through which gas can flow into and out of the resonator volume. Due to a specifically adapted geometry of the neck and resonator volume, the gas column in the neck oscillates at a characteristic frequency, resulting in effective sound absorption of certain frequencies within the resonator volume. In practice, Helmholtz resonators are frequently used to reduce noise and resonances in wind tunnels, in building acoustics, or in vehicle exhaust systems to selectively dampen disruptive frequencies. Often, Helmholtz resonators are used to dampen relatively low frequencies, for example, in the range of 0.1 to 10 Hz and its multiples, or 0.01 Hz to 20 Hz and its multiples, where other damping measures are often less effective. Helmholtz resonators can be used, in particular, to eliminate or dampen resonances in a room or wind tunnel. The resonator volume of the Helmholtz resonator is connected to the room or wind tunnel via a neck or tube. With a fixed room size (volume V) and a fixed cross-sectional area A of the neck, the frequency of the Helmholtz resonator can be adjusted within a certain range by changing the neck length L. In a wind tunnel, frequency shifts are to be expected at different wind speeds, meaning that different frequencies must be dampened at different wind speeds, and consequently, different Helmholtz resonators are required. Alternatively, the Helmholtz resonator can have a degree of adjustability with respect to its resonant frequency. Ideally, the neck length should be continuously adjustable to achieve stepless frequency adjustment. The DE 10 2019 215 650 A1 In this context, this describes a continuously variable-length cavity resonator, specifically a Helmholtz resonator, used for damping low-frequency pressure fluctuations in wind tunnels. The resonator neck consists of a fixed-length and a variable-length section. The variable-length section is formed by segments of sidewall elements whose effective length can be altered. The sidewall elements can be plate-shaped and/or elastic to allow angling and displacement. In the transition zone between the neck sections are deflection guides with a curved bearing opening, which enables the angling of the sidewall elements. The sidewall elements are moved simultaneously and parallel to each other, thus allowing the length of the resonator neck to be changed. The DE 10 2021 103 187 A1 This document describes a variable Helmholtz resonator for a motor vehicle that dampens unwanted noise. The resonator consists of three main parts: an inlet opening, a neck, and a resonator volume. The described Helmholtz resonator can automatically adjust its damping characteristics to the pressure ratio between gas pressure and ambient pressure. A spring element allows the resonator to return to its original position. The damping characteristics are adjusted by changing the expansion of the resonator volume and/or the length and/or diameter of the neck. From the EP 3 156 664 A1 An adjustable resonator arrangement is known that can be used to reduce acoustic emissions in gas systems. The arrangement consists of a resonator cavity with a throat opening connected to a conduit system through which gas can flow. A resonator tuning structure, connected to a movable upper wall of the resonator cavity, projects from the cavity. A preload mechanism, such as a spring, holds the tuning structure in an initial position in which the throat opening is closed. As gas flows through the conduit system, the tuning structure moves and opens the throat opening of the resonator by a predetermined degree. This movement also changes the size of the resonator volume, since the upper wall is connected to a movable side wall. This allows the resonant frequency of the cavity to be adjusted to the varying acoustic frequency of the gas flow. This stepless adjustment of the neck length or resonator volume is technically demanding. A simpler approach is to adjust the neck length in predefined steps. However, this method is likely to result in inaccurate adjustments to the required frequencies, with steps that are too coarse and the exact frequency to be damped not being precisely targeted. Consequently, the resonator's full potential is not utilized. It is therefore an object of the present invention to provide a Helmholtz resonator whose resonant frequency can be easily adjusted with sufficient accuracy. In particular, a Helmholtz resonator suitable for avoiding unwanted resonances in a wind tunnel is desirable. The problem is solved by a Helmholtz resonator with a resonator volume and a resonator neck having a plurality of side walls, wherein the resonator neck is designed such that the size of at least one surfa