Active tip-clearance control

Last updated

Active clearance control (ACC) is a method used in large aircraft gas turbines to improve fuel efficiency during cruise. This is achieved by setting the turbine tip clearance at more than one operating point and contrasts with passive clearance control which sets it for only one condition and is explained below.

Contents

CFM International CFM56-5B engine showing turbine tip clearance control: piccolo tubes round LPT case and (immediately to the left) smooth outer surface of HPT case cooling manifold CFM56 P1220759.jpg
CFM International CFM56-5B engine showing turbine tip clearance control: piccolo tubes round LPT case and (immediately to the left) smooth outer surface of HPT case cooling manifold

As one way to reduce fuel consumption better blade tip sealing has taken on a prominent role in aircraft engine design since the late 1960's. [2] It is used on the CFM International CFM56-5B engine, installed on the Airbus A320, for example. [3]

Background

Blade tip sealing has been a challenging problem since the development of the gas turbine engine. It is such because the clearance between the blade tips and surrounding casing (shroud) tends to vary due primarily to changes in thermal and mechanical loads on the rotating (turbine wheel) and stationary (stator, turbine casing) structures. [2]

Turbine tip clearance is a leakage path for gas which doesn't flow past the turbine blade aerofoil so doesn't contribute to the power developed by the turbine. As such it reflects a waste of fuel (reduced fuel efficiency). The clearance depends on the thermal growth of a thick-section turbine disc compared to a thin-section turbine case, and also disc radial growth with speed. [2] The three vary, and hence tip clearance, with the engine running condition and clearance is a minimum when the engine first accelerates from idle to take-off, it hasn't had a chance to heat up evenly from being cold at idle although the bladed turbine disc is at maximum speed and so has maximum radial growth from the centrifugal stresses. The thermal effects take longer to stabilize at a steady temperature, ie to give an unvarying tip clearance. This transient condition which gives a minimum clearance is known as a pinch point. The setting of the clearance when the engine is built such that the blade tips don't rub the stationary shrouds in the turbine case at a pinch point condition may be known as passive clearance control. [4]

HPT (high pressure turbine) blade tip clearance has a significant impact on fuel burn and emissions [5] so using ACC gives significant benefits in cruise fuel burn, range, and payload capability for long range aircraft. [5]

Basic system overview

As an example the CFM International CFM56-5A engine active clearance control uses HPC air for the HPTACC and fan bypass air for the LPTACC. Clearance control is managed by the engine FADEC which consists of an electronic control unit (ECU), an hydromechanical unit (HMU) and HP and LP ACC valves. [6]

Related Research Articles

<span class="mw-page-title-main">Turbine</span> Rotary mechanical device that extracts energy from a fluid flow

A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels.

<span class="mw-page-title-main">Pratt & Whitney</span> Aircraft engine manufacturer

Pratt & Whitney is an American aerospace manufacturer with global service operations. It is a subsidiary of RTX Corporation. Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut. The company is the world's second largest commercial aircraft engine manufacturer, with a 35% market share as of 2020. In addition to aircraft engines, Pratt & Whitney manufactures gas turbine engines for industrial use, marine propulsion, and power generation. In 2017, the company reported that it supported more than 11,000 customers in 180 countries around the world.

<span class="mw-page-title-main">Turbofan</span> Airbreathing jet engine designed to provide thrust by driving a fan

A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a combination of the preceding generation engine technology of the turbojet, and a reference to the additional fan stage added. It consists of a gas turbine engine which achieves mechanical energy from combustion, and a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.

<span class="mw-page-title-main">Airbus A320 family</span> European airliner family

The Airbus A320 family is a series of narrow-body airliners developed and produced by Airbus. The A320 was launched in March 1984, first flew on 22 February 1987, and was introduced in April 1988 by Air France. The first member of the family was followed by the longer A321, the shorter A319, and the even shorter A318 . Final assembly takes place in Toulouse in France; Hamburg in Germany; Tianjin in China since 2009; and Mobile, Alabama in the United States since April 2016.

<span class="mw-page-title-main">Airbus A318</span> Airliner, part of the A320 family

The Airbus A318 is the smallest and least numerous variant airliner of the Airbus A320 family. The A318 carries 107 to 132 passengers and has a maximum range of 5,750 kilometres. Final assembly of the aircraft took place in Hamburg, Germany. It is intended primarily for short-range service.

<span class="mw-page-title-main">CFM International CFM56</span> Turbofan aircraft engine

The CFM International CFM56 series is a Franco-American family of high-bypass turbofan aircraft engines made by CFM International (CFMI), with a thrust range of 18,500 to 34,000 lbf. CFMI is a 50–50 joint-owned company of Safran Aircraft Engines of France, and GE Aerospace (GE) of the United States. GE produces the high-pressure compressor, combustor, and high-pressure turbine, Safran manufactures the fan, gearbox, exhaust and the low-pressure turbine, and some components are made by Avio of Italy and Honeywell from the US. Both companies have their own final assembly line, GE in Evendale, Ohio, and Safran in Villaroche, France. The engine initially had extremely slow sales but has gone on to become the most used turbofan aircraft engine in the world.

<span class="mw-page-title-main">Propfan</span> Type of aircraft engine

A propfan, also called an open rotor engine, open fan engine or unducted fan, is a type of aircraft engine related in concept to both the turboprop and turbofan, but distinct from both. The design is intended to offer the speed and performance of a turbofan, with the fuel economy of a turboprop. A propfan is typically designed with a large number of short, highly twisted blades, similar to the (ducted) fan in a turbofan engine. For this reason, the propfan has been variously described as an "unducted fan" (UDF) or an "ultra-high-bypass (UHB) turbofan".

<span class="mw-page-title-main">IAE V2500</span> High-bypass turbofan engine

The IAE V2500 is a two-shaft high-bypass turbofan engine built by International Aero Engines (IAE) which powers the Airbus A320 family, the McDonnell Douglas MD-90, and the Embraer C-390 Millennium.

<span class="mw-page-title-main">General Electric TF39</span> Turbofan aircraft engine

The General Electric TF39 is a high-bypass turbofan engine that was developed to power the Lockheed C-5 Galaxy. The TF39 was the first high-power, high-bypass jet engine developed. The TF39 was further developed into the CF6 series of engines, and formed the basis of the LM2500 and LM6000 marine and industrial gas turbine. On September 7, 2017, the last active C-5A powered with TF39 engines made its final flight to Davis-Monthan Air Force Base for retirement. The TF39 was effectively retired, and all remaining active C-5 Galaxys are now powered by F138 engines.

<span class="mw-page-title-main">CFM International</span> Franco-American aerospace manufacturer

CFM International is a Franco-American aircraft engine manufacturer. The company is a joint venture between GE Aerospace and Safran Aircraft Engines and is headquartered in Cincinnati, Ohio. It was founded in 1974 to build and support the CFM56 series of turbofan engines. CFM is the world's largest commercial aircraft engine manufacturer, with a 39% market share as of 2020. It has delivered more than 37,500 of its engines to more than 570 operators. The name CFM is derived from the two parent companies' commercial engine designations: GE's CF series and Snecma's M series.

<span class="mw-page-title-main">Pratt & Whitney J58</span> High-speed jet engine by Pratt & Whitney

The Pratt & Whitney J58 is an American jet engine that powered the Lockheed A-12, and subsequently the YF-12 and the SR-71 aircraft. It was an afterburning turbojet engine with a unique compressor bleed to the afterburner that gave increased thrust at high speeds. Because of the wide speed range of the aircraft, the engine needed two modes of operation to take it from stationary on the ground to 2,000 mph (3,200 km/h) at altitude. It was a conventional afterburning turbojet for take-off and acceleration to Mach 2 and then used permanent compressor bleed to the afterburner above Mach 2. The way the engine worked at cruise led it to be described as "acting like a turboramjet". It has also been described as a turboramjet based on incorrect statements describing the turbomachinery as being completely bypassed.

<span class="mw-page-title-main">Rolls-Royce Trent 500</span> 1990s British turbofan aircraft engine

The Rolls-Royce Trent 500 is a high-bypass turbofan produced by Rolls-Royce to power the larger A340-500/600 variants. It was selected in June 1997, first ran in May 1999, first flew in June 2000, and achieved certification on 15 December 2000. It entered service in July 2002 and 524 engines were delivered on-wing until the A340 production ended in 2012.

<span class="mw-page-title-main">Rolls-Royce Trent 900</span> 2000s British turbofan aircraft engine

The Rolls-Royce Trent 900 is a high-bypass turbofan produced by Rolls-Royce plc to power the Airbus A380, competing with the Engine Alliance GP7000. Initially proposed for the Boeing 747-500/600X in July 1996, this first application was later abandoned but it was offered for the A3XX, launched as the A380 in December 2000. It first ran on 18 March 2003, made its maiden flight on 17 May 2004 on an A340 testbed, and was certified by the EASA on 29 October 2004. Producing up to 374 kN (84,000 lbf), the Trent 900 has the three shaft architecture of the Rolls-Royce Trent family with a 2.95 m (116 in) fan. It has a 8.5–8.7:1 bypass ratio and a 37–39:1 overall pressure ratio.

IAE International Aero Engines AG is a Zürich-registered joint venture aeroengine manufacturing company.

A jet engine performs by converting fuel into thrust. How well it performs is an indication of what proportion of its fuel goes to waste. It transfers heat from burning fuel to air passing through the engine. In doing so it produces thrust work when propelling a vehicle but a lot of the fuel is wasted and only appears as heat. Propulsion engineers aim to minimize the degradation of fuel energy into unusable thermal energy. Increased emphasis on performance improvements for commercial airliners came in the 1970s from the rising cost of fuel.

<span class="mw-page-title-main">Pratt & Whitney PW1000G</span> Geared turbofan engine produced beginning 2007

The Pratt & Whitney PW1000G family, also known as the GTF, is a family of high-bypass geared turbofan produced by Pratt & Whitney. Following years of development and testing on various demonstrators, the program officially launched in 2008 with the PW1200G destined for the Mitsubishi SpaceJet. The first successful flight test occurred later that year. The PW1500G variant, designed for the Airbus A220, became the first certified engine in 2013. The program cost is estimated at $10 billion.

<span class="mw-page-title-main">CFM International LEAP</span> Aircraft turbofan engine, successor to the CFM56

The CFM International LEAP is a high-bypass turbofan engine produced by CFM International, a 50–50 joint venture between American GE Aerospace and French Safran Aircraft Engines. It is the successor of the CFM56 and competes with the Pratt & Whitney PW1000G to power narrow-body aircraft.

<span class="mw-page-title-main">Components of jet engines</span> Brief description of components needed for jet engines

This article briefly describes the components and systems found in jet engines.

<span class="mw-page-title-main">General Electric Passport</span> High bypass turbofan aircraft engine

The General Electric Passport is a turbofan developed by GE Aerospace for large business jets. It was selected in 2010 to power the Bombardier Global 7500 and 8000, first run on June 24, 2013, and first flown in 2015. It was certified in April 2016 and powered the Global 7500 first flight on November 4, 2016, before its 2018 introduction. It produces 14,000 to 20,000 lbf of thrust, a range previously covered by the General Electric CF34. A smaller scaled CFM LEAP, it is a twin-spool axial engine with a 5.6:1 bypass ratio and a 45:1 overall pressure ratio and is noted for its large one-piece 52 in (130 cm) fan 18-blade titanium blisk.

The familiar study of jet aircraft treats jet thrust with a "black box" description which only looks at what goes into the jet engine, air and fuel, and what comes out, exhaust gas and an unbalanced force. This force, called thrust, is the sum of the momentum difference between entry and exit and any unbalanced pressure force between entry and exit, as explained in "Thrust calculation".

References

Notes
  1. "CFM56 comes of age"Flight International 18 April 1981, CFM56-2 cutaway drawing key p.1121
  2. 1 2 3 "Turbine Engine Clearance Control Systems: Current Practices and Future Directions" (PDF). September 2002. Retrieved 2017-04-03.
  3. Airbus Training Simulator A320 Flight Crew Operating Manual, Power Plant Fuel System, 1.70.40 P 2, SEQ 005, REV 23, P1,2
  4. NASA TM/2002-211794, Turbine Engine Clearance Control Systems:Current Practices And Future Directions, Lattime and Steinetz, September 2002, Fig.4 and p.10
  5. 1 2 Nasa (October 2005). "HTP Clearance control" (PDF). Retrieved 2017-04-03.
  6. Training Manual CFM 56-5A Engine Systems, April 2000, published by CFMI Customer Training Center