Patent Description:
The outflow valve (OFV), typically a butterfly valve, is used by the cabin pressurization system of an aircraft to control the cabin pressure as required by the cabin environmental controller. Followed by fuselage leakages, the OFV is the main fuselage opening responsible to exhaust excess pressurized air that is constantly introduced into the aircraft cabin to improve air quality and maintain the desired cabin pressure (i.e., so as to avoid the use of supplemental oxygen masks by passengers and crew). The OFV is therefore responsible for controlling cabin pressure and as such the pressure differential at the OFV equals the difference between the interior cabin pressure and ambient external atmospheric pressure. When embodied as a butterfly valve, the OFV may be modulated as needed by an on-board aircraft environmental controller so as to achieve a desired interior cabin pressurization set point. As can be appreciated the pressure differential at the OFV can be high enough to produce supersonic flow (sometimes reaching up to a Mach number of <NUM>) when the aircraft is in cruise flight in the flight level altitudes.

The art solutions to the problem of reducing noise of discharge pressurized air from the OFV has essentially taken two approaches, namely altering the noise source or reducing the acoustic propagation efficiency. More specifically, OFV noise generation is frequently mitigated by employing vortex generators (VGs) to increase flow turbulence of the discharged pressurized air, which can then in turn reduce boundary layer flow separation and dampen the buildup of coherent acoustic sources. VGs can be located at the valve flap or on the valve case (upstream or downstream of the valve flap), with a variety of shapes and quantities. Although usually effective, they alter a complex part such as the OFV which also affects the aircraft cabin pressurization system and its control laws.

A second alternative is to reduce the effectiveness of acoustic propagation downstream of the OFV, such as by using acoustic mufflers or by the addition of a physical damping barrier to sound propagation along the critical sound path. The drawbacks of this alternative solution include not only the large weight and cost impact of the acoustic mufflers, but also the fact that acoustic mufflers added at the OFV exhaust may increase the system pressure loss, affecting the cabin pressurization system and hence cabin comfort. <CIT> discloses a ventilation system for an aircraft with an outlet valve positioned in the outer shell of the aircraft, having a first inlet opening for exhaust air from an electronics area and a second inlet opening for cabin air, and wherein one single outlet opening is provided. <CIT> discloses a mechanism to control aircraft cabin pressure, comprising, in combination, a cylindrical gate valve, a second cylinder surrounding said gate valve, a nozzle mounted at one end of said second cylinder, said second cylinder having openings to the cabin at the circumferential edge of the nozzle, said nozzle having an area normal to the airstream progressively decreasing from said circumferential edge so as to smoothly accelerate the air flow from said cabin, and said nozzle arranged as a valve seat for cooperating with one end of said cylindrical gate valve, said one end of said gate valve being formed with a substantially knife-like edge for contacting said nozzle, said valve including an air motor piston formed a part of said valve, said piston projecting laterally from said valve member and slidably mounted in the second cylinder, and air power means for operatively adjusting said piston so as to regulate said valve. <CIT> discloses an aircraft air distribution assembly providing integrated personally controllable air flow and cabin air flow. The aircraft air distribution assembly comprises a plenum and a flow restriction system. The plenum is connected to a plurality of personal air outlets configured to provide the personally controllable air flow. The flow restriction system extends through at least one wall of the plenum, the flow restriction system configured to set a pressure for the cabin air flow. <CIT> discloses a mechanism for controlling the pressure within an enclosure by means of a relief valve.

It would therefore be highly desirable if the OFV could be provided with passive acoustic mitigation so as to reduce cabin noise level when pressurized air is discharged from the cabin to maintain target cabin pressurization and comfort. It is towards fulfilling such need that the embodiments disclosed herein are directed.

The present invention provides an outflow valve exhaust nozzle according to claim <NUM>, an aircraft pressurization system according to claim <NUM> and an aircraft according to claim <NUM>. Examples thereof are detailed in the dependent claims. Broadly, the embodiments disclosed herein are directed toward outflow valve (OFV) exhaust nozzle for an aircraft pressurization system. In accordance with a described embodiment the exhaust nozzle includes an upstream section which includes a cylindrical solid wall that follows the internal diameter of the OFV, and a downstream section fixed to the upstream section, the downstream section including a solid exhaust wall having a circumferential portion which includes a series of air intake perforations.

At least one vortex generator is rigidly attached to the solid exhaust wall and includes a vortex generating section protruding inwardly into the exhaust nozzle. According to some embodiments, a pair of such vortex generators are provided which may diverge outwardly from one another relative to airflow within the nozzle. Each vortex generator may include a base fixed to an exterior surface of the cylindrical solid wall of the upstream section whereby the vortex generating section of each of the vortex generators may extend at substantially a right angle relative to the base thereof. According to certain embodiments, the solid exhaust wall of the upstream section defines a pair of slots such that each of the vortex generating sections of the vortex generators extends through a respective one of the slots. The vortex generating section of each vortex generator may be generally triangular or provided with virtually any wing-shape that achieves the desired vortex generating functions.

The series of air intake perforations may be arranged in a regular or irregular pattern with the individual perforations being substantially circular. The series of air intake perforations may be provided in any circumferential portion of the exhaust wall that is between about <NUM>% to about <NUM>% of the total exterior surface area of the solid exhaust wall, sometimes between about <NUM>% to about <NUM>% of such total exterior surface area.

The exhaust valve may usefully be employed in an aircraft pressurization system which includes an outflow valve (OFV), typically a butterfly valve, in fluid communication with pressurized air of the aircraft cabin, and an exhaust nozzle as described briefly hereinabove attached to a discharge end of the OFV.

These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.

The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which:.

Accompanying <FIG> schematically depicts an outflow valve exhaust nozzle <NUM> associated with an aircraft pressurization system PS employed to pressurize the interior cabin IC of an aircraft fuselage AF. It will be understood in this regard that only a forward portion of the fuselage AF is depicted in <FIG> and that the aircraft shown would include a cylindrical fuselage with a suitable aft bulkhead to allow the interior cabin IC to be pressurized by the pressurization system PS.

As schematically depicted, the pressurization system PS draws pressurized bleed air from the compressor section of the turbofans associated with the port and starboard engines Ep and Es, respectively. The pressurized bleed air is temperature adjusted by a heat exchanger HE using cold ram air such that the pressurized conditioned air may be introduced into the interior cabin IC by way of the flow control valve FCV. A pressure sensor P senses pressure of the interior cabin IC and sends pressure signal to the cabin environmental controller EC which in turn operates the flow control valve FCV via a command signal so as to maintain the interior cabin IC within a predetermined pressurization condition that is dependent upon the altitude of the cruise flight. In order to maintain the pressurization condition within the interior cabin at the predetermined pressurization condition, the environmental controller issues a command signal to open/close outflow valve OFV so as to allow pressurized cabin air to be exhausted when needed through the exhaust nozzle <NUM> and thereby prevent under- and over-pressurization of the interior cabin IC.

As is seen in <FIG> and <FIG>, the outflow butterfly valve OFV is typically positioned immediately upstream of the exhaust nozzle <NUM>. The pressurized air that is discharged through the outflow butterfly valve OFV and into the exhaust nozzle <NUM> may conveniently be exhausted to the ambient external pressure environment at a location that does not affect the aerodynamic performance of the aircraft. In the embodiment shown in <FIG> and <FIG>, the pressurized air exhausted through the nozzle <NUM> may conveniently be directed into the wing-fuselage fairing cavity FC of the wing-fuselage fairing WF aft of the wing stub WS.

The exhaust nozzle <NUM> is perhaps better depicted in accompanying <FIG>. As shown, the exhaust nozzle <NUM> is generally comprised of a cylindrical upstream solid wall section <NUM> and a frustroconical solid exhaust wall section <NUM> downstream of the section <NUM>. Although in the embodiment depicted, the downstream solid exhaust wall section <NUM> is frustroconical, it may be provided in any duct shape form that adapts to the cylindrical interface of the OFV internal diameter. The upstream edge portion 12a of the upstream section <NUM> is attached to the discharge end of the outflow valve OFV by any suitable mechanical fasteners, e.g., rivets, screws, bolt/nut assemblies and the like positioned within the circumferentially spaced apart connection openings (a representative few of which are identified by reference numeral 12b in the FIGURES).

Important to the noise mitigation characteristics of the nozzle <NUM>, an array or series of substantially circular air intake perforations (a representative few of which are identified by reference numeral 14a in the FIGURES) are provided in any circumferential portion of the downstream solid exhaust wall <NUM>. The particular size and geometric arrangement of the perforations 14a are not critical as those in this art could provide the specific number, size and/or arrangement necessary to allow air from the ambient pressure environment (i.e., so-called unpressurized air that has not been pressurized by the aircraft pressurization system) to be introduced into the boundary layer of discharged pressurized air in the interior of the perforated exhaust duct of the solid exhaust wall <NUM> of the nozzle <NUM> thereby reducing adverse pressure gradients therewithin which in turn results in a more attached air flow. The perforations 14a therefore do not need to be provided along the entire area of the solid exhaust wall <NUM> since a fully perforated exhaust duct would cause airflow detachment in regions where there already exists a properly attached boundary layer on the solid cone (such as on the diametrical opposite side of the perforated solid exhaust <NUM>), resulting in a less efficient system with a higher exhaust pressure loss. The pattern of the perforations 14a does not need to be regular as is depicted in the FIGURES nor do the diameters of the perforations need to be of any particular size provided they are sufficiently large to allow air to flow through the upper portion of the downstream solid exhaust wall <NUM> while still retaining the required structural integrity of the duct wall. Thus, in preferred forms, the perforations 14a will be formed in any circumferential portion of the solid exhaust wall <NUM> that is between about <NUM>% to about <NUM>%, typically between about <NUM>% to <NUM>% of the total exterior surface area of the solid exhaust wall <NUM>.

The embodiment of the discharge nozzle <NUM> shown in <FIG> will also preferably include one or more vortex generators <NUM> rigidly attached to the nozzle <NUM> upstream of the perforations 14a. The vortex generators <NUM> will typically be in the form of a one-piece (unitary) angled metal component having a base section 16a rigidly attached to the nozzle <NUM> (e.g., to an exterior surface of the cylindrical wall of the upstream section <NUM>) via any suitable fastening element (e.g., rivets, screws, bolt/nut assemblies and the like). A vortex generating section 16b having a generally triangular or trapezoidal shape (or other suitable wing-shape having similar aerodynamic functions) extends at substantially a right angle (i.e., <NUM>° +/- about <NUM>°) through a slot 16c in the cylindrical wall of the upstream section <NUM> and protrudes into the airflow of the pressurized air being discharged into the nozzle <NUM> from the outflow valve OFV.

In the depicted embodiment a pair of vortex generators <NUM> is provided which are fixed to the solid upstream wall section <NUM> so as to outwardly diverge relative to the airflow within the nozzle <NUM>. Moreover, in the depicted embodiment it is preferred that the vortex generators be positioned substantially symmetrically relative to a centerline CL (see <FIG>) of the array of perforations 14a. The positioning of the vortex generators <NUM> will induce vortices of reverse direction to cancel the vortices emanating from the pressurized air discharged from the outflow valve OFV). The nozzle <NUM> according to the embodiments described herein thus allow the placement of rather large vortex generators downstream of the outflow valve OFV which in turn improves the vortices that are generated thereby. As a result, attachment of the boundary layer of airflow is improved with the advantage that relatively complex component parts, such as the outflow valve OFV and the associated cabin pressurization system, do not need to be modified.

The array of perforations 14a and a pair of divergently angled vortex generators <NUM> upstream of such perforations in the exhaust nozzle <NUM> do not increase weight while effectively reducing the in-flight cabin noise levels by up to about 3dB in the interior cabin regions affected by this noise source. Since they are designed so as to not increase the pressure loss at the outflow valve OFV exhaust, the implementation the embodiments described herein will also not affect the cabin pressurization system nor the passenger comfort during opening and closing of cabin doors.

Claim 1:
An outflow valve exhaust nozzle (<NUM>) for an aircraft pressurization system (PS), wherein the nozzle (<NUM>) is configured to exhaust pressurized air that is discharged through an outflow valve (OFV) into the nozzle (<NUM>) to an ambient external pressure environment, the nozzle (<NUM>) comprising:
an upstream solid wall section (<NUM>) configured to be attached to a discharge end of the outflow valve (OFV); and
a downstream solid exhaust wall section (<NUM>) fixed to the upstream solid wall section (<NUM>), the downstream solid exhaust wall section (<NUM>) including a circumferential portion which includes a series of air intake perforations (14a) configured to allow unpressurized air from the ambient external pressure environment to be introduced into a boundary layer of discharged pressurized air in the interior of the downstream solid exhaust wall section (<NUM>).