Effective Date: 15 June 98
Ventilation
Powerplant ventilation on the airplane includes ventilation in the high bypass engine nacelle and also the pylon and center engine installation. Powerplant ventilation flow rates and volume change rates, both on the ground and in-flight will be calculated to verify that adequate ventilation is provided. FAA has received from airframe manfactuer and engine manfactuer, the design values for flow rates and volume change rates for the powerplant ventilation system.
The method of calculating powerplant ventilation will consist of measuring pressures and air temperatures in each individual compartment and then by using these data, calculating the flow rates and volume change rates for each compartment. The calculated volume change rate will then be compared against the minimum required volume change rate to determine if the flow rate through each compartment is adequate.
Flow and Volume Change Rate Calculation
The basic equation required to calculate flow rate in an individual compartment will be that used for an orifice:
W = (C.A)#2g ### - lbm/sec .................................... (1)
where,
W = Airflow rate, lbm/sec
CdA = Effective orifice area, ft2
g = Gravitational constant factor 32.174 lbm-ft/lbf-sec2
# = Air density just downstream of the orifice, lbm/ft3
P = Static pressure difference across orifice, lbf/ft2
The basic equation used to calculate volume change rate in a compartment will be:
N = (W/# V)60, change/minute ......................................... (2)
where,
N = Compartment volume change rate, changes/minute
# = Average air density in the compartment, lbm/ft3
V = Compartment volume, ft3
Engine Nacelle Ventilation
Nacelle ventilation is divided basically into five individual zones; these are Zone 1, Zone 2, Zone 3, Zone 4A and Zone 4B. Their location for a wing engine installation and center engine installation can be seen on Figures 1 and 2, respectively.
Zone 1 - Ventilation for Zone 1 is provided when airborne by ram airflow from an inlet on the nose cowl for a wing engine and on the left side of the vertical stabilizer for a center engine. It enters the zone from a manifold at the top and is exhausted through an ejector outlet at the bottom. The flow rate and volume change rate will be calculated according to equations (1) and (2), respectively, described above.
When ground running the engine, there is no ventilation provided for Zone 1.
Zone 2 - Low Pressure (L.P.) compressor (fan) discharge air provides cooling and ventilation around the gas generator. Air enters through controlled gaps between the sections of the gas generator fairings and the majority returns to the fan stream through four semi-circular (hooded) outlets; the remainder of the Zone 2 flow flows out through the drains mast. The total flow rate is calculated based on outlet conditions of the four Zone 2 vents, using Equation (1), and from model test data for the drains mast. The volume change rate will be calculated using Equation (2).
Zone 3 - L.P. compressor (fan) discharge air at total pressure enters at the leading edge of the splitter fairing to provide a cooling flow over the Intermediate Pressure (I.P.) and High Pressure (H.P.) air off-take ducts for Zone 3. A diaphragm forward of the rear mount allows a portion of the flowto enter Zone 4B while the remainder flows into Zone 4A. The flow rate for Zone 3 is calculated based on the inlet conditions to Zone 3 at the splitter fairing. The equations to be used are presented above.
Zone 4A - Zone 4A air is supplied from Zone 3 through two holes in the splitter compartmant floor and exhausted through a diaphragm into the final compartment, Zone 4B. The flow rate and volume change rate are calculated based on outlet condition at the diaphragm between Zone 4A and 4B using the equations presented above.
Zone 4B - Zone 4B receives its ventilation air from Zones 3 and 4A and discharges via the annular outlet gap between the stowed jet spoiler doors and the primary nozzle assembly. The flow rate is calculated based on the exit conditions from both Zones 3 and 4A. The equations presented above are used to calculate the flow rate and volume change rate for Zone 4B.
Pylon Ventilation
Ventilation air enters through a slot at the juncture of the pylon to the leading edge section of the wing. A small distribution chamber, which is located adjacent to the inlet, divides the flow between the wing leading edge section and the forward portion of the pylon cavity. After discharge into the pylon cavity, the air moves aft and exhausts overboard through the louver exit as shown in Figure 1. The flow rate in the pylon is calculated based on exhaust conditions at the louver exit. The volume change rate is calculated based on average conditions throughout the pylon. The equations required are presented above. Since the Cd of the louver varies greatly with flight conditions, an iteration using Figure 3 is required to define the actual discharge coefficient.
Engine Support Structure (ESS)
Ventilation air enters through two aft facing louvers on either side of the vertical stabilizer, see Figure 2. After circulating through the compartment, the air is then exhausted through two annuli in the Thermal Barrier Web. This air is then finally exhausted overboard forward of the APU compartment. The flow rate through the ESS is calculated based on exhaust conditions at the web. The flow rate and volume change rate calculations are presented above.
Nose Cowl - Wing Engine
Flow rate and volume change rate will not be determined for the nose cowl compartment. The only analysis to be performed is to determine if the nose cowl is at a higher or lower pressure than the adjacent compartment, Zone 1.
Fire Zones
The designated fire areas for this powerplant system are Zone 1, Zone 2, Zone 4A and Zone 4B. The non-designated fire areas are Zone 3, the ESS, pylon, and nose cowl. The minimum volume change rates are specified for designated and non-designated fire areas.
Ventilation Flow Rate Evaluation
An evaluation to determine the adequacy of the ventilation flow rates will be made by comparing the calculated change rates to the minimum requirements. Following the complete evaluation of the ventilation flow rate, the data obtained during testing will be normalized and plotted similar to the following:
This format will be used only for the engine nacelle ventilation flows being supplied from the fan stream.
The format anticipated for the normalized data for the ram air used in Zone 1, the pylon, and the ESS compartment is presented below.
Temperature Survey
Accessory, component, and propulsion environmental temperatures will be measured on both a wing pod and a center engine installation during typical flight conditions, including soaks and cool-downs.
Analysis of the temperature data consists of extrapolating recorded temperatures to hot day conditions and determining that sufficient cooling is being supplied. Accessory, environmental, structural, and fluid temperatures will be extrapolated on a 1:1 basis to hot day conditions defined as 120 Deg F and 130 Deg F at sea level, with a 3.6 Deg F per 1000 ft. lapse rate, as defined in Reference 6; the hot day temperature as a function of altitude is shown in Figure 1.